Authorship：Lead author,　Corresponding author   Publishing type：Research paper (international conference proceedings)  

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (international conference proceedings)  

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (international conference proceedings)  

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Authorship：Last author   Publishing type：Research paper (international conference proceedings)  

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Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Temporally and spatially resolved laser-induced breakdown spectroscopy (LIBS) was applied to a four-stroke, single-cylinder test engine’s cyclic exhaust gas to demonstrate engine performance. The LIBS technique provided quantitative air-to-fuel ratio (A/F) measurements by generating localized breakdown plasma during the compression and exhaust strokes. The results showed that the timing and duration settings of the emission energy ionization and molecular spectra affect the intensity peaks. Optimum measurements performed between 200 ns and 10 ms after breakdown resulted in observed atomic spectra of CI (248 nm), Hβ (485 nm), Hα (656 nm), NI (745, 824 nm), and OI (777, 844 nm). The intensities of CI (248 nm) and Hα (656 nm) decreased with increasing A/F, whereas the intensity ratios of NI and OI remained constant. A decrease in the intensity ratio of C/O and Hα/O was observed as the A/F increased. This study is a major step toward defining a means of using LIBS to control the A/F ratio in gasoline engines by focusing on the exhaust gas rather than the flame.

DOI： 10.3390/en15093053

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.fuel.2021.123049

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s13762-022-04010-4

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Other Link： https://link.springer.com/article/10.1007/s13762-022-04010-4/fulltext.html

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Biogas, a renewable and alternative energy, has recently gained attention as an environmentally friendly fuel for power generation in internal combustion (IC) engines. This study aimed to investigate the effect of the carbon dioxide (CO2) to methane (CH4) ratio in a dual-fuel gas engine. It is known that gaseous fuel combustion at high loads is accompanied by knocking if an appropriate combustion controlling strategy is not applied. Therefore, premixed mixture ignition in the end-gas region (PREMIER) combustion was proposed under high load conditions. Experiments were carried out using a dual-fuel gas engine under supercharged conditions, with an intake pressure of 200 kPa. Simulated biogas consisting of CH4 and CO2 was used as a primary fuel and diesel was used as a pilot fuel. The pilot fuel injection timing was varied during the experiments. The indicated mean effective pressure (IMEP) and thermal efficiency increased as injection timing was advanced. With the addition of CO2, the thermal efficiency of PREMIER combustion was slightly increased, although the IMEP was slightly decreased. The unburned gas temperature for PREMIER combustion increases as a function of the CO2 content of the mixture. Due to compression by flame propagation, high unburned gas temperatures in dual-fuel gas engines are important for achieving autoignition inside the end-gas region under PREMIER combustion conditions.

DOI： 10.1016/j.fuel.2020.119330

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (international conference proceedings)  

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Publishing type：Research paper (international conference proceedings)  

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Ain Shams Engineering Journal

DOI： 10.1016/j.asej.2019.12.003

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Publishing type：Research paper (scientific journal)   Publisher：National Library of Serbia  

The phenomena of binary collisions and coalescence of droplets was
investigated from experimental studies but still are missing from real
applications such as from fuel injector. The main purpose of the current
study is to investigate the phenomena of binary collisions and coalescence
of droplets from a practical port fuel injector (PFI). To accomplish this,
direct microscopic images are taken from high-speed video camera coupled
with a long-distance microscope and Barlow lens using the backlighting
method. Experimental optimization of the spatial resolution and the depth
-of -field of the long-distance microscope and Barlow lens are achieved.
Experimental results from the direct microscopic images are compared with
predictions from empirical equations for different collision regimes.
Droplet sizes and velocities of experimental coalescence droplets from
collisions are compared with the values predicted by the equations. The main
results of this study are: The probability of collision and coalescence is
very low in a PFI. The tangential velocity components of small droplets play
an essential role in shape deformation during collisions and coalescence of
the droplets. The previous published empirical equations to calculate
dimensionless parameters, the Weber number (We), the droplet diameter ratio
(?), and impact parameter (B) are applicable to the coalescence of droplets
in a PFI.

DOI： 10.2298/tsci191120185a

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Publishing type：Research paper (international conference proceedings)  

© 2019 SAE Japan and SAE International. The authors have previously proposed a plume ignition and combustion concept (i.e., PCC combustion), in which a hydrogen fuel is directly injected to the combustion chamber in the latter half of compression stroke and forms a richer mixture plume. By combusting the plume, both cooling losses and NOx formation are reduced. In this study, thermal efficiency was substantially improved and NOx formation was reduced with PCC combustion by optimizing such characteristics as direction and diameter of the jets in combination with combustion of lean mixture. Output power declined due to the lean mixture, however, was recovered by supercharging while keeping NOx emissions at the same level. Thermal efficiency was further improved by slightly re-optimizing the jet conditions. The results showed that the hydrogen engine can attain near-zero emissions of NOx reduced to the single-digit ppm level with high thermal efficiency close to 50 percent and can thus be truly called a near-zero emission engine.

DOI： 10.4271/2019-01-2306

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Publishing type：Research paper (international conference proceedings)  

© 2019 SAE Japan and SAE International. In this research, a spark plug with an optical fiber has been developed to obtain the emission spectra from the spark discharge and flame kernel. This developed spark plug with an optical fiber can obtain the time series of emission spectra from the spark discharge and Initial flame kernel in the real spark-ignition engine using EMCCD spectrometer. The plasma vibrational temperature of the spark discharge can be measured using the emission spectra from the electrically excited CN violet band system. The plasma of the spark discharge and gas rotational temperature of the initial flame kernel can be also measured using emission spectra from OH∗ radicals (P and R branches). The plasma temperature of the spark discharge was almost 8,000 K and the gas temperature of the Initial flame kernel approached that of the adiabatic flame temperature.

DOI： 10.4271/2019-01-2158

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

To improve the thermal efficiency of internal combustion engines at high loads, premixed mixture ignition in the end-gas region (PREMIER) combustion is proposed as a precursor to knocking. In the current work, a pilot fuelignited dual-fuel gas engine was operated at constant speed under different intake pressures (101, 150, and 200 kPa). A simulated biogas was served as the primary fuel and diesel as the pilot fuel. The maximum mean effective pressure and thermal efficiency were evident during PREMIER operation because of autoignition in the end-gas region. Similar to knocking combustion, PREMIER combustion features two stages but neither pressure oscillation nor a rapid pressure rise is observed. We here define a new parameter, the PREMIER intensity (PI), which reflects the strength of PREMIER combustion. As the injection timing was advanced and the pressure boosted, more cycles underwent end-gas autoignition; the associated heat release increased and, consequently, the PI value rose. When the pressure and temperature of a premixed fuel mixture rose as injection timing was advanced, end-gas autoignition commenced earlier. The end-gas autoignition delay became shorter as intake pressure was increased and injection timing advanced.

DOI： 10.1016/j.fuel.2019.115634

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (international conference proceedings)  

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Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE INC  

PREMIER (PREmixed Mixture Ignition in the End-gas Region) combustion occurs with auto-ignition in the end-gas region when the main combustion flame propagation is nearly finished. Auto-ignition is triggered by the increases in pressure and temperature induced by the main combustion flame. Similarly to engine knocking, heat is released in two stages when engines undergo this type of combustion. This pattern of heat release does not occur during normal combustion. However, engine knocking induces pressure oscillations that cause fatal damage to engines, whereas PREMIER combustion does not. The purpose of this study was to elucidate PREMIER combustion in natural gas spark-ignition engines, and differentiate the causes of knocking and PREMIER combustion. We applied combustion visualization and in-cylinder pressure analysis using a compression-expansion machine (CEM) to investigate the auto-ignition characteristics in the end-gas region of a natural gas spark-ignition engine. We occasionally observed knocking accompanied by pressure oscillations under the spark timings and initial gas conditions used to generate PREMIER combustion. No pressure oscillations were observed during normal and PREMIER combustion. Auto-ignition in the end-gas region was found to induce a secondary increase in pressure before the combustion flame reached the cylinder wall, during both knocking and PREMIER combustion. The auto-ignited flame area spread faster during knocking than during PREMIER combustion. This caused a sudden pressure difference and imbalance between the flame propagation region and the end-gas region, followed by a pressure oscillation. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

DOI： 10.1016/j.proci.2018.08.055

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Publishing type：Part of collection (book)  

Current energy and emission regulations set the requirements to increase the use of natural gas in engines for transportation and power generation. The characteristics of natural gas are high octane number, less amount of carbon in the molecule, suitable to lean combustion, less ignitibility, etc. There are some advantages of using natural gas for engine combustion. First, less carbon dioxide is emitted due to its molecular characteristics. Second, higher thermal efficiency is achieved owing to the high compression ratio compared to that of gasoline engines. Natural gas has higher octane number so that knock is hard to occur even at high compression ratios. However, this becomes a disadvantage in homogeneous charge compression ignition (HCCI) engines or compression ignition engines because the initial auto-ignition is difficult to be achieved. When natural gas is used in a diesel engine, primary natural gas–air mixture is ignited with small amount of diesel fuel. It was found that under high pressure, lean conditions, and with the control of certain parameters, the end gas is auto-ignited without knock and improves the engine combustion efficiency. Recently, some new fuel ignition technologies have been developed to be applied to natural gas engines. These are the laser-assisted and plasma-assisted ignition systems with high energy and compact size.

DOI： 10.1007/978-981-13-3307-1_8

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© 2018 SAE International. All Rights Reserved. The present study helps to understand the local combustion characteristics of PREmixed Mixture Ignition in the End-gas Region (PREMIER) combustion mode while using increasing amount of natural gas as a diesel substitute in conventional CI engine. In order to reduce NOx emission and diesel fuel consumption micro-pilot diesel injection in premixed natural gas-air mixture is a promising technique. New strategy has been employed to simulate dual fuel combustion which uses well established combustion models. Main focus of the simulation is at detection of an end gas ignition, and creating an unified modeling approach for dual fuel combustion. In this study G-equation flame propagation model is used with detailed chemistry in order to detect end-gas ignition in overall low temperature combustion. This combustion simulation model is validated using comparison with experimental data for dual fuel engine.

DOI： 10.4271/2018-01-0199

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

We investigated time-resolved ultraviolet-visible (UV-vis) light absorbance to identify the formation behaviour of formaldehyde (HCHO) and hydroxyl (OH) within the wavelength range of 280-400 nm in a homogeneous charge compression ignition (HCCI) engine fuelled with dimethyl ether (DME). The time-resolved HCHO and OH profiles at different initial pressures showed that HCHO absorbance increased in the low-temperature reaction (LTR) and thermal-ignition preparation (TIP) regions and decreased gradually as the combustion approached the high-temperature reaction (HTR) region. At higher intake pressures, HCHO absorbance decreased and OH absorbance increased. The time-resolved absorbance spectra of HCHO, with peaks at 316, 328, 340, and 354 nm for all combustion cycles, were evaluated and it was found that average absorption at 328 nm was slightly higher than at 316, 340, and 354 nm. For knocking combustion cycles, the absorbance of HCHO in the LTR region was high for cycles with low knock intensity and low for cycles with high knock intensity, showing a high level of OH absorbance. Chemical kinetics analyses showed that for different fuel/oxidiser ratios, initial O-2 concentration and intake temperature had no effect on in-cylinder temperatures in the LTR or TIP regions. However, they did have significant effects on HTR combustion. In-cylinder temperature in the LTR region had less effect on HCHO and H2O2 formation than pressure.

DOI： 10.1016/j.fuel.2017.09.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A new combustion process called the Plume Ignition Combustion Concept (PCC), in which the plume tail of the hydrogen jet is spark-ignited immediately after the completion of fuel injection to accomplish combustion of a rich mixture has been proposed by the authors. This PCC combustion process markedly reduces nitrogen oxides (NOx) emissions in the high-output region while maintaining high levels of thermal efficiency and power. On the other hand, as burning lean mixture of fuel and air is the conventional way to improve thermal efficiency and reduce NOx, a high lambda premixed mixture of hydrogen and air formed by injecting hydrogen in the early stage of the compression stroke has been used in direct injection hydrogen engines. It was recently reported, however, that this mixture condition does not always offer expected improved thermal efficiency under even lean mixture conditions by increasing unburned hydrogen emissions caused by incomplete flame propagation in the non-uniform and extremely lean portion of the mixture. In this study, the effect of retarding the injection timing to late in the compression stroke but slightly advanced from original PCC was examined as a way of reducing unburned hydrogen emissions and improving thermal efficiency. These effects result from a centroidal axially stratified mixture that positions a fairly rich. charge near the spark plug. This stratified mixture is presumably effective in reducing incomplete flame propagation thought to be the cause of unburned hydrogen emissions and also promoting increasing burning velocity of the mixture that improve thermal efficiency. Finally, this research is characterized by measuring the hydrogen fuel concentration at the point and the time of spark ignition quantitatively by spark-induced breakdown spectroscopy in order to identify the changes in mixture ratio mentioned above caused by the parameters involved. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2017.08.015

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

A comprehensive chemical kinetics and computational fluid-dynamics (CFD) analysis were performed to evaluate the combustion of syngas derived from biomass and coke-oven solid feedstock in a micro-pilot ignited supercharged dual-fuel engine under lean conditions. The developed syngas chemical kinetics mechanism was validated by comparing ignition delay, in-cylinder pressure, temperature and laminar flame speed predictions against corresponding experimental and simulated data obtained by using the most commonly used chemical kinetics mechanisms developed by other authors. Sensitivity analysis showed that reactivity of syngas mixtures was found to be governed by H-2 and CO chemistry for hydrogen concentrations lower than 50% and mostly by H-2 chemistry for hydrogen concentrations higher than 50%. In the mechanism validation, particular emphasis is placed on predicting the combustion under high pressure conditions. For high hydrogen concentration in syngas under high pressure, the reactions HO2 + HO2 = H2O2 + O-2 and H2O2 + H = H-2 + HO2 were found to play important role in in-cylinder combustion and heat production. The rate constants for H2O2 + H = H-2 + HO2 reaction showed strong sensitivity to high-pressure ignition times and has considerable uncertainty. Developed mechanism was used in CFD analysis to predict in-cylinder combustion of syngas and results were compared with experimental data. Crank angle-resolved spatial distribution of in-cylinder spray and combustion temperature was obtained. The constructed mechanism showed the closest prediction of combustion for both biomass and cokeoven syngas in a micro-pilot ignited supercharged dual-fuel engine. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.fuel.2017.04.125

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We used a multi-hole injector to spray isooctane under atmospheric conditions and observed droplet impingement behaviors. It is generally known that droplet impact regimes such as splashing, deposition, or bouncing are governed by the Weber number. However, owing to its complexity, little has been reported on microscopic visualization of poly-dispersed spray. During the spray impingement process, a large number of droplets approach, hit, then interact with the wall. It is therefore difficult to focus on a single droplet and observe the impingement process. We solved this difficulty using highspeed microscopic visualization. The spray/wall interaction processes were recorded by a high-speed camera (Shimadzu HPV-X2) with a long-distance microscope. We captured several impinging microscopic droplets. After optimizing the magnification and frame rate, the atomization behaviors, splashing and deposition, were recorded. Then, we processed the images obtained to determine droplet parameters such as the diameter, velocity, and impingement angle. Based on this information, the critical threshold between splashing and deposition was investigated in terms of the normal and parallel components of the Weber number with respect to the wall. The results suggested that, on a dry wall, we should set the normal critical Weber number to 300.

DOI： 10.1117/12.2270691

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE INC  

The spark discharge ignition process was investigated using simultaneous temperature measurements of the spark discharges and the initial flame kernel. We were able for the first time to measure a time series of emission spectra from the spark discharge and initial flame kernel inside a spark-ignition engine using a spectrometer coupled with a spark plug and optical fiber. The plasma vibrational temperature of the spark discharge can be measured using time series emission spectra from the electrically excited CN* violet band system. The gas rotational temperature of the initial flame kernel can also be measured using emission spectra from OH* radicals (P and R branches). Simultaneously, visualization of the spark discharge and a time series of emission spectra inside a spark-ignition engine were performed under homogeneous mixture conditions, to eliminate the effects of stratification of temperature and mixture concentrations around the spark plug. We discuss thermal energy transfer from the spark discharge to the combustible mixture. The main conclusions that can be drawn from this study are as follows. CN* emission can be detected from the spark discharge, visualized using a high-speed camera during the arc discharge phase. Our results confirmed that the plasma temperature of the spark discharge was nearly 6800 K and that thermal energy was transferred from the spark plasma channel to the combustible mixture. The gas temperature of the initial flame kernel approached that of the adiabatic flame temperature. (C) 2016 by The Combustion Institute. Published by Elsevier Inc.

DOI： 10.1016/j.proci.2016.08.029

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

The effects of split pilot fuel injection on engine performance and PREmixed Mixture Ignition in the End Gas Region (PREMIER) combustion characteristics were investigated in a single-cylinder dual-fuel natural gas engine ignited with diesel fuel. In particular, the effect of second spray timing on combustion mode was examined. PREMIER combustion was observed in a wider range of operating conditions with split injection strategy compared to single injection strategy. We determined that it was possible to both decelerate heat release and suppress knocking to PREMIER combustion, and accelerate heat release and promote normal combustion to PREMIER combustion, with suitable second injection timing. The maximum of thermal efficiency of PREMIER combustion operation with split injection was close to the results obtained with knocking operation. In-cylinder images showed that split injection strategy advances or retards the progress of combustion by controlling the size and rate of growth of flame kernels, depending on the timing of the second injection. The combustion progress is earlier when the pilot fuel delivered during the first injection autoignites during the second injection. Kernel growth and the final size were adversely affected when the second injection was initiated after pilot fuel autoignition. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.fuel.2016.07.120

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Biogas is a renewable alternative fuel for internal combustion engines that has several advantages over conventional fuels, including lower costs and reduced levels of harmful emissions. In particular, it exhibits a neutral recirculation loop for carbon dioxide (CO2), which is one of the main causes of global warming. In this study, we investigated biogas fuels with various compositions using a micro co-generation engine system. The ratio of methane to CO2 and engine load were varied, and the intake air and fuel flow rates were controlled to change the equivalence ratio. The results show that for a given engine load, the ignition delay and combustion period increased with CO2 content, and the combustion speed decreased. The fuel consumption increased slightly with CO2 content; however, the thermal efficiency improved using a lean burn strategy, resulting in lower nitrogen oxide (NOx) emission, and moreover, the use of biogas with the stoichiometric air-fuel ratio appears effective in reducing NOx emissions and can improve the fuel economy at higher loads. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.apenergy.2016.08.152

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

We conducted experiments to investigate in-cylinder light absorption by carbon dioxide (CO2) during homogeneous charge compression ignition (HCCI) engine combustion. The combustion was fuelled with dimethyl ether. An in situ laser infrared absorption method was developed. We used an optical fibre spark plug sensor and the light source was a 4.301 mu m quantum cascade laser (QCL). We applied Lambert Beer's law in the case of a single absorption line of CO2. We were able to measure the transient CO2 formation during the HCCI combustion inside the engine cylinder. Our experiments showed that the laser light transmissivity level decreased with the intensity of the infrared (IR) signal. We compared the change in the transmissivity to the spatially integrated HCCI flame luminosity level and observed significant correlations between the flame luminosity level, heat release rate and transmissivity. Time-resolved experiments showed that the CO2 absorbance increases when the second peak of the rate of heat release (ROHR) is maximised. After combustion, the CO2 concentration was approximately 4 vol%, which agrees with the amount of CO2 formed during complete combustion. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.fuel.2016.06.040

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Quantitative measurements of local fuel concentrations were conducted in a direct injection hydrogen spark-ignition research engine using the spark-induced breakdown spectroscopy (SIBS) technique. For SIBS measurements, a new sensor was developed from a commercially available M12-type spark plug with no major modifications to the electrodes. The new plug sensor showed better durability and required less maintenance when used in a hydrogen research engine. Emission spectra from the plasma generated by the spark plug were collected through an optical fibre housed in the centre electrode of the plug and resolved spectrally for atomic emissions of Ha, 0(I), and N(I). The main focus of the present work was to characterise the effects of ambient pressure at ignition timing on spectral line emissions and to improve the accuracy of SIBS measurements by taking into account the pressure dependency of atomic emissions. A significant effect of the corresponding pressure at ignition timing was observed on spark-induced breakdown spectroscopic measurements and emission line characteristics. Retarded spark timing (i.e. higher ambient pressure at the ignition site) resulted in lower spectral line intensities as well as weaker background emissions. It is well established that with relatively higher pressure and density of atoms or molecules, the cooling of expanding plasma accelerates, and the collision probability increases, leading to both a weaker broadband continuum and atomic emissions. A "calibration MAP" representing the correlation of air excess ratio (relative air/fuel ratio) with both intensity ratio and pressure at ignition timing was created and subsequently used for quantitative measurements of local fuel concentrations for both port injection and direct injection strategies to demonstrate and explore the effects of pressure dependency of atomic emission on the accuracy of the SIBS measurements. Local stratification of the fuel mixture in the vicinity of the spark gap location associated with direct injection strategies was confirmed; the coefficient of variation of the local air excess ratio was relatively small for measurements made using the calibration map. This demonstrated that the measurement accuracy of local fuel concentrations through a spark plug sensor can be improved significantly when the pressure dependency of atomic emissions is taken into account. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2016.05.280

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INT UNION CRYSTALLOGRAPHY  

Measurement of combustion gas by high-energy X-ray Compton scattering is reported. The intensity of Compton-scattered X-rays has shown a position dependence across the flame of the combustion gas, allowing us to estimate the temperature distribution of the combustion flame. The energy spectra of Compton-scattered X-rays have revealed a significant difference across the combustion reaction zone, which enables us to detect the combustion reaction. These results demonstrate that high-energy X-ray Compton scattering can be employed as an in situ technique to probe inside a combustion reaction.

DOI： 10.1107/S1600577516001740

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Ethanol is a particularly promising bio-fuel, which is already widely used in the transportation sector. Much research has focused on laser ignition in internal combustion engines, because it offers a number of significant advantages. The motivation of this study is to reduce the higher cost of anhydrous ethanol by enabling the direct use of wet ethanol for combustion applications. This study reports the effects of water content on the laser ignition characteristics of air-ethanol flames with 0-40% water by volume added to the ethanol. Laser-induced breakdown was generated by focusing a 532-nm nanosecond pulse from a Q-switched Nd:YAG laser. High-speed visualisation of the combustion was achieved, together with analyses of the in-chamber pressure history, mass fraction burned, and ignition delay over a range of equivalence ratios. Removing the final 20% of water from ethanol is particularly energy intensive. The results of this investigation revealed that the flame growth rate and flame propagation velocity are both increased by adding up to 20% water (by volume) to ethanol, indicating a positive effect of the water at relatively low concentrations. It was also found that the ignition delay was shorter as the water content was increased up to a volume fraction of 20%. Therefore, it can be hypothesised that the presence of water enhances the ionisation process and increases the rate of radical generation during laser-induced breakdown of wet ethanol. Numerical analysis using the commercial software package CHEMKIN-PRO revealed a reduction in adiabatic flame temperature and laminar burning velocity due to the addition of water to ethanol. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.fuel.2015.10.067

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We report an investigation of the effects of the ambient pressure on fuel concentration measurements of an injected jet of hydrogen using spark-induced breakdown spectroscopy (SIBS) in a constant-volume vessel. Measurements were carried out using hydrogen injected into a nitrogen environment with different ambient pressures, and the local concentrations were measured at various spark locations. The optical emission from the spark discharge at 501 nm (corresponding to nitrogen) and 656 nm (corresponding to hydrogen) was observed using SIBS. Spectrally resolved emission from the plasma was detected simultaneously using a spectrometer. The potential to determine the hydrogen/nitrogen ratio in the spark gap using was demonstrated. Spectral calibration was carried out using a hydrogen/nitrogen mixture, and hydrogen was injected at a pressure of 5.0 MPa into nitrogen with ambient pressures in the range 0.5-1.5 MPa. The results show an increase in the background radiation, as well as of the peaks corresponding to hydrogen and nitrogen atomic emission lines, as the ambient pressure increased. An increase in the density of nitrogen inside the chamber influenced the structure of the hydrogen jet, slowing the spray and reducing penetration, which altered the equivalence ratio at the location of the spark. When the spark occurred during injection, the behavior of the hydrogen jet was quasi-steady state; when the spark timing followed the injection, however, an unsteady state was observed. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2015.01.121

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

In this work, spark-induced breakdown spectroscopy (SIBS) was employed to investigate the mixing process of a hydrogen jet in a constant-volume vessel. The local fuel concentration of the hydrogen jet was measured at several locations, using a SIBS sensor. A high-speed camera was used to visualize spark discharge fluctuations, and hydrogen jet concentration measurements were conducted simultaneously. Spectrally resolved atomic emissions from the plasma generated by the spark plug were examined to determine the local equivalence ratio. Direct visualization of the spark discharge provided useful information about the influence of spark discharge characteristics related to the spark timing. Using the developed SIBS sensor, atomic emission spectra were obtained from hydrogen H-alpha at 656 nm and nitrogen N (I) at 501 nm. Comparison of the intensity peaks of atomic emissions from hydrogen and nitrogen allows the local hydrogen concentration in a measured volume to be determined, and hence also the local equivalence ratio. The measurement results demonstrate the local variation in the equivalence ratio throughout the jet and along its axis. From the results, the spatial structure of the hydrogen jet affects the hydrogen/nitrogen mixing and could be clarified with SIBS technique when the spark is discharged. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2014.08.146

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Language：English   Publisher：OPTICAL SOC AMER  

The behaviors of laser-induced plasma and fuel spray were investigated by visualizing images with an ultra-high-speed camera. Timeseries images of laser-induced plasma in a transient spray were visualized using a high-speed color camera. The effects of a shockwave generated from the laser-induced plasma on the evaporated spray behavior were investigated. The interaction between a single droplet and the laser-induced plasma was investigated using a single droplet levitated by an ultrasonic levitator. Two main conclusions were drawn from these experiments: (1) the fuel droplets in the spray were dispersed by the shockwave generated from the laser-induced plasma; and (2) the plasma position may have shifted due to breakdown of the droplet surface and the lens effect of droplets. (C) 2013 Optical Society of America

DOI： 10.1364/OE.22.000A44

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE INC  

Spark-ignition (SI) hydrogen engines based on direct injection (DI) promise significant advantages in terms of thermal efficiency and power output, and present a means of overcoming problems related to knocking, backfiring, and preignition. A better understanding of the effects of hydrogen jets on the fuel concentration distribution and mixing process in a DISI engine should provide new and useful insights into combustion optimization. The objective of the present work was to gain a deeper comprehension of the characteristics of late-injection hydrogen combustion. An experimental combustion setup was applied to a fired, jet-guided DISI engine operated at 600 rpm in stratified mode. GDI injector with the jet directed toward the spark plug was used to develop the stratified combustion concept. A high-speed camera synchronized with the spark was focused on a 52 mm-diameter field of view through a window at the bottom of the piston crown. A series of single-shot images captured at different intervals was used to study the time evolution of the flame distribution. Variations in the fuel injection timing relative ignition timing were found to impact the development of the early flame, as well as the flame propagation. This research also employed spark-induced breakdown spectroscopy (SIBS) to measure the local fuel-air concentration in the spark gap at the time of ignition under stratified-charge conditions. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

DOI： 10.1016/j.proci.2012.06.103

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Experiments were conducted in a compression-expansion test engine to investigate the combustion characteristics in a homogeneous charge compression ignition (HCCI) engine fuelled with dimethyl ether. Two types of analyses were performed. In the first, ultraviolet-visible (UV-Vis) light absorbance was investigated to identify the formation behaviour of HCHO and OH during HCCI combustion. In the second, knocking combustion was investigated by analysing the spatially integrated flame luminosity and in-cylinder pressure oscillations. The time-resolved HCHO and OH profiles at different equivalence ratios showed that HCHO absorbance increased in the low-temperature reaction (LTR) and thermal-preparation regions and gradually decreased as the combustion approached the high-temperature reaction (HTR) region. The in-cylinder temperature in the LTR region had little effect on the rate of the maximum pressure rise, and this did not change much at different equivalence ratios. The results demonstrated that there was a marked difference between the intensity of the flame emissions of non-knocking and knocking events. The time-resolved integrated absorbance spectra of HCHO with peaks at 328, 340, and 354 nm that occurred before the OH peaks appeared suggested that when a certain threshold ratio of (dP/d theta R-LT)/(dP/d theta(HTR)) was reached, the amount of HCHO decreased due to reactions in the thermal-preparation region while the tendency to knock increased. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.fuel.2012.03.033

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The effects of spray impingement, injection parameters, and exhaust gas recirculation (EGR) on the combustion characteristics and exhaust emissions of a premixed charge compression ignition (PCCI) diesel engine were investigated using a single-cylinder test engine and an optically accessible engine. Tests were carried out under constant speed with variable injection pressures and EGR rates. Exhaust emissions and in-cylinder pressures were measured under all experimental conditions. Analyses were conducted based on diesel spray evolution and combustion process visualisation coupled with performance and exhaust emissions. Higher injection pressures led to lower smoke, hydrocarbons (HC), and nitrogen oxide (NOx) emissions but had roughly the same CO emissions compared with lower injection pressures. Higher EGR rates led to the simultaneous reduction in NOx and soot emissions due to lower combustion temperatures compared to conventional diesel combustion. However, HC and CO emissions increased due to fuel impingement, bulk quenching, and over-mixing, leading to an air fuel mixture that was too lean to burn. An optimum spray targeting spot was identified, leading to lower emissions of soot, CO, and HC but higher NOx emissions without EGR. The simultaneous reduction in NOx and soot was achieved using the optimum spray targeting spot by introducing EGR, which was accompanied by homogenous combustion and a low luminosity flame attributed to fuel impingement on the piston bowl wall. (C) 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.applthermaleng.2011.11.011

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SAGE PUBLICATIONS LTD  

This paper is concerned with engine experiments and spectroscopic analysis of premixed mixture ignition in the end-gas region (PREMIER) combustion in a pilot fuel ignited, natural gas dual-fuel engine. The results reveal the characteristics and operating parameters that induce and affect this combustion mode. The PREMIER combustion is followed by natural gas flame propagation. Pilot-injected diesel fuel ignites the natural gas/air mixture, and the flame propagates before the natural gas/air mixture is autoignited in the end-gas region. This combustion cycle differs from a knocking cycle in terms of combustion and emission characteristics. The PREMIER combustion can be controlled by pilot fuel injection timing, the equivalence ratio, and the exhaust gas recirculation (EGR) rate, and can be used as an effective method for high load extension on a dual-fuel engine. An analysis of the relationship between the maximum in-cylinder pressure and its crank angle (CA) is used to compare combustion dynamics during conventional, PREMIER, and knocking combustion. In PREMIER combustion, the heat release gradually transforms from the slower first-stage flame rate to the faster second-stage rate. During PREMIER combustion, the maximum indicated mean effective pressure (IMEP) and thermal efficiency increase by about 25 per cent compared with those of conventional combustion, and low carbon monoxide (CO) and total hydrocarbon (HC) emissions can be achieved. However, nitrogen oxide (NO(x)) emissions increase. Spectroscopic analysis shows that the intensity of the OH* emissions in the end-gas region increases as the combustion mode transforms from conventional to PREMIER to knocking. In all three modes, emission fluctuations above 650 nm can be observed in the end-gas region. These emissions are attributed to the luminosity from soot particles formed during the concurrent diesel fuel combustion.

DOI： 10.1177/1468087411409664

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A multidimensional computational fluid dynamics (CFD) simulation of a constructed syngas chemical kinetic mechanism was performed to evaluate the combustion of syngas in a supercharged dual-fuel engine for various syngas initial compositions under lean conditions. The modelled results were validated by comparing predictions against corresponding experimental data for a supercharged dual-fuel engine. The predicted and measured in-cylinder pressure, temperature, and rate of heat release (ROHR) data were in good agreement. The effect of the hydrogen peroxide chain-propagation reaction on the progress of combustion under supercharged conditions was examined for different types of syngas using various initial H-2 concentrations. The effect of the main syngas kinetic mechanism reactions on the combustion progress was analysed in terms of their contribution to the total heat of the reaction. The best results compared with experimental data were obtained in the range of equivalence ratios below about 0.8 for all types of syngas considered in this paper. As the equivalence ratio increased above 0.8, the results deviated from the experiment data. The spatial distribution of the in-cylinder temperature and OH center dot within this equivalence-ratio range showed the completeness of the combustion. The present CFD model captured the overall combustion process well and could be further developed into a useful tool for syngas-engine combustion simulations. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2011.07.140

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The objective of this study was to investigate the performance and emissions of a pilot-ignited, supercharged, dual-fuel engine powered by different types of syngas at various equivalence ratios. It was found that if certain operating conditions were maintained, conventional engine combustion could be transformed into combustion with two-stage heat release. This mode of combustion has been investigated in previous studies with natural gas, and has been given the name PREmixed Mixture Ignition in the End-gas Region (PREMIER) combustion. PREMIER combustion begins as premixed flame propagation, and then, because of mixture autoignition in the end-gas region, ahead of the propagating flame front, a transition occurs, with a rapid increase in the heat release rate. It was determined that the mass of fuel burned during the second stage affected the rate of maximum pressure rise. As the fuel mass fraction burned during the second stage increased, the rate of maximum pressure rise also increased, with a gradual decrease in the delay between the first increase in the heat release rate following pilot fuel injection and the point when the transition to the second stage occurred. The H(2) and CO(2) content of syngas affected the engine performance and emissions. Increased H2 content led to higher combustion temperatures and efficiency, lower CO and HC emissions, but higher NOx emissions. Increased CO2 content influenced performance and emissions only when it reached a certain level. In the most recent studies, the mean combustion temperature, indicated thermal efficiency, and NOx emissions decreased only when the CO2 content of the syngas increased to 34%. PREMIER combustion did not have a major effect on engine cycle-to-cycle variation. The coefficient of variation of the indicated mean effective pressure (COV(IMEP)) was less than 4% for all types of fuel at various equivalence ratios, indicating that the combustion was within the stability range for engine operation. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2011.04.192

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

This study investigated the engine performance and emissions of a supercharged engine fueled by hydrogen (H(2)), and three other hydrogen-containing gaseous fuels such as primary fuels, and diesel as pilot fuel in dual-fuel mode. The energy share of primary fuels was about 90% or more, and the rest of the energy was supplied by diesel fuel. The hydrogen-containing fuels tested in this study were 13.7% H(2)-content producer gas, 20% H(2)-content producer gas and 56.8% H(2)-content coke oven gas (COG). Experiments were carried out at a constant pilot injection pressure and pilot quantity for different fuel air equivalence ratios and at various injection timings. The experimental strategy was to optimize the pilot injection timing to maximize engine power at different fuel air equivalence ratios without knocking and within the limit of the maximum cylinder pressure. Better thermal efficiency was obtained with the increase in H(2) content in the fuels, and neat H(2) as a primary fuel produced the highest thermal efficiency. The fuel air equivalence ratio was decreased with the increase in H(2) content in the fuels to avoid knocking. Thus, neat H(2)-operation produced less maximum power than other fuels, because of much leaner operations. Two-stage combustion was obtained; this is an indicator of maximum power output conditions and a precursor of knocking combustion. The emissions of CO and HC with neat H(2)-operation were 98-99.9% and NOx about 85-90% less than other fuels. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2011.03.070

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE INC  

Cycle-resolved residual gas fraction measurements were made inside a heavy-duty diesel engine using an infrared absorption method. An in situ laser infrared absorption method was developed using an optical fiber sensor and a 4.301-mu m quantum cascade laser (QCL) as the light source. We discuss the feasibility of obtaining in situ CO2 concentration measurements inside the engine combustion chamber using the newly developed optical fiber sensor system. Lambert-Beer's law can be applied for the case of a single absorption line of CO2, and the dependence of the CO2 molar absorption coefficient on the ambient pressure and temperature of was determined using a constant volume vessel. This coefficient decreased with increasing pressure, indicating almost constant at pressures over 1.0 MPa. CO2 concentration measurements were made in a compression-expansion engine in order to calibrate the measurement system. The feasibility of the optical fiber sensor system was then investigated in a heavy-duty diesel engine. We were able to measure the CO2 concentration inside the combustion chamber under various engine load conditions and were able to determine the internal exhaust gas recirculation (EGR) ratio. This measurement technique proved to be valuable in obtaining the cycle-to-cycle CO2 concentration of the residual gas in a heavy-duty diesel engine. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

DOI： 10.1016/j.proci.2010.07.017

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

The effects of compression ratio and simulated exhaust-gas recirculation (EGR) on combustion characteristics and exhaust emissions of a diesel PCCI engine were investigated using a single-cylinder test engine. Tests were carried out under constant speed with various compression ratios and EGR rates. Exhaust emissions and in-cylinder pressure were measured for all experimental conditions. Analyses based on engine performance and exhaust emissions were conducted. An optimum compression ratio that provided better indicated thermal efficiency and IMEP while yielding lower emissions of smoke, HC, and CO, and reasonable NOx without EGR was identified. High rates of EGR led to the simultaneous reduction of NOx and soot emissions due to a lower combustion temperature compared with conventional diesel combustion, with a slight penalty in HC and CO.

DOI： 10.1299/jtst.6.463

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Vaporized fuel concentration in a spray-guided direct-injection spark-ignition (SG-DISI) engine was measured using an optical sensor installed in a spark plug. A laser infrared absorption method was applied to quantify the instantaneous gasoline concentration near the spark plug. This paper discusses the feasibility of obtaining in situ air-fuel ratio measurements with this sensor installed inside an SG-DISI engine cylinder. First, the effects of the spray plume from a multi-hole injector on the vaporized fuel concentration measurements near the spark-plug sensor were examined using a visible laser. We determined the best position for the sensor in the engine, which was critical due to the spray and vapor plume formation. Then, a 3.392-mu m He-Ne laser that coincided with the absorption line of the hydrocarbons was used as a light source to examine the stratified mixture found during ultra-lean engine operation. A combustible mixture existed around the spark plug during the injection period when a preset air-fuel ratio of 45.0 was used with different fuel injection timings and net mean effect pressure conditions. The effects of the orientation of the spark plug on the measured results and ignitability of the SG-DISI engine were examined. Orienting the spark plug vertically to one of the spray plumes provided more accurate results and better engine reliability. The study demonstrated that it was possible to qualify the air-fuel ratio near the spark plug during the injection period using the developed spark-plug sensor in an SG-DISI engine.

DOI： 10.1007/s00348-010-0884-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The main objective of this study is to observe and investigate the phenomena of atomization, i.e. the fuel break-up process very close to the nozzle exit of a practical port fuel injector (PFI). In order to achieve this objective, direct microscopic images of the atomization process were obtained using an ultra-high-speed video camera that could record 102 frames at rates of up to 1 Mfps, coupled with a long-distance microscope and Barlow lens. The experiments were carried out using a PFI in a closed chamber at atmospheric pressure. Time-series images of the spray behaviour were obtained with a high temporal resolution using backlighting. The direct microscopic images of a liquid column break-up were compared with experimental results from laser-induced exciplex fluorescence (LIEF), and the wavelength obtained from the experimental results compared with that predicated from the Kelvin-Helmholtz break-up model. The droplet size diameters from a ligament break-up were compared with results predicated from Weber's analysis. Furthermore, experimental results of the mean droplet diameter from a direct microscopic image were compared with the results obtained from phase Doppler anemometry (PDA) experimental results. Three conclusions were obtained from this study. The atomization processes and detailed characterizations of the break-up of a liquid column were identified; the direct microscopic image results were in good agreement with the results obtained from LIEF, experimental results of the wavelength were in good agreement with those from the Kelvin-Helmholtz break-up model. The break-up process of liquid ligaments into droplets was investigated, and Weber's analysis of the predicated droplet diameter from ligament break-up was found to be applicable only at larger wavelengths. Finally, the direct microscopic image method and PDA method give qualitatively similar trends for droplet size distribution and quantitatively similar values of Sauter mean diameter.

DOI： 10.1088/0957-0233/21/7/075403

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

This study investigated the engine performance and emissions of a supercharged engine fueled by hydrogen and ignited by a pilot amount of diesel fuel in dual-fuel mode. The engine was tested for use as a cogeneration engine, so power output while maintaining a reasonable thermal efficiency was important. Experiments were carried out at a constant pilot injection pressure and pilot quantity for different fuel-air equivalence ratios and at various injection timings without and with charge dilution. The experimental strategy was to optimize the injection timing to maximize engine power at different fuel-air equivalence ratios without knocking and within the limit of the maximum cylinder pressure. The engine was tested first with hydrogen-operation condition up to the maximum possible fuel-air equivalence ratio of 0.3. A maximum IMEP of 908 kPa and a thermal efficiency of about 42% were obtained. Equivalence ratio could not be further increased due to knocking of the engine. The emission of CO was only about 5 ppm, and that of HC was about 15 ppm. However, the NOx emissions were high, 100-200 ppm or more. The charge dilution by N-2 was then performed to obtain lower NOx emissions. The 100% reduction of NOx was achieved. Due to the dilution by N-2 gas, higher amount of energy could be supplied from hydrogen without knocking, and about 13% higher IMEP was produced than without charge dilution. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2009.11.009

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

The interaction of spray and combustion processes forms a complex system of physical phenomena undergoing in IC engines. Studying this interaction is important to determine strategies for simultaneously reducing soot and NOx emissions from diesel engines. Spray combustion interactions are evaluated by the flame lift-off length - the distance from the injector orifice to the location of hydroxyl luminescence closest to the injector in the flame jet. Various works have been dedicated to successful simulations of lifted flames of a diesel jet by use of various combustion modeling approaches. In this work, flame surface density and flamelet concepts were used to model the diesel lift-off length. Numerical studies have been performed with the ECFM3Z model and n-Heptane fuel to determine the flame lift-off length under quiescent conditions. The numerical results showed good agreement with experimental data, which were obtained from an optically accessible constant volume chamber and presented at the Engine Combustion Network (ECN) of Sandia National Laboratories. It was shown that at a certain distance downstream from the injector orifice, stoichiometric scalar dissipation rate matched the extinction scalar dissipation rate. This computed extinction scalar dissipation rate correlated well with the flame lift-off length. For the range of conditions investigated, adequate quantitative agreement was obtained with the experimental measurements of lift-off length under various ambient gas O-2 concentrations and ambient gas densities.

DOI： 10.1299/jtst.5.238

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

The spray from a multi-hole injector applied to direct injection spark ignition (DISI) engine was investigated. In order to understand the detailed structure of the transient spray near the nozzle a combined LDA/PDA system was used. PDA system was optimized in order to detect relative smaller droplets. Size-classified technique was used to get deep information about the spray characterizations near nozzle. The experiments were performed at 7 MPa of injection pressure. At early stage of spray the droplet velocity distribution in the centre of the spray showed high value. Smaller droplets under 15 mu m showing followability to air flow, while larger droplets over 20 mu m will have drag due to momentum decay. Droplets of 15<D <= 20 mu m in diameter is criteria for follow/penetration near the nozzle. Near the nozzle, the atomization predominantly occurs at the centre region of the spray.

DOI： 10.1299/jtst.5.36

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

This study investigated the engine performance and emissions of a supercharged dual-fuel engine fueled by hydrogen-rich coke oven gas and ignited by a pilot amount of diesel fuel. The engine was tested for use as a cogeneration engine, so power output while maintaining a reasonable thermal efficiency was important Experiments were carried out at a constant pilot injection pressure and pilot quantity for different fuel-air equivalence ratios and at various injection timings without and with exhaust gas recirculation (EGR). The experimental strategy was to optimize the injection timing to maximize engine power at different fuel-air equivalence ratios without knocking and within the limit of the maximum cylinder pressure. The engine was tested first without EGR condition up to the maximum possible fuel-air equivalence ratio of 0 65. A maximum indicated mean effective pressure (IMEP) of 1425 kPa and a thermal efficiency of 39% were obtained. However, the nitrogen oxides (NOx) emissions were high. A simulated EGR up to 50% was then performed to obtain lower NOx emissions. The maximum reduction of NOx was 60% or more maintaining the similar levels of IMEP and thermal efficiency. Two-stage combustion was obtained; this is an indicator of maximum power output conditions and a precursor of knocking combustion. (C) 2009 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reserved.

DOI： 10.1016/j.ijhydene.2009.09.016

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

This study determined the local equivalence ratio of a CH(4)/air mixture in a laminar premixed flame using spark-induced breakdown spectroscopy (SIBS) with a fiber-coupled intensified charge coupled device (ICCD) spectrometer. Spectrally resolved emission spectra of plasma generated by a spark plug were investigated for their potential to measure local fuel concentrations in a premixed mixture. The influence of key parameters, such as the camera gate timing and spark energy, on the intensity of radical emission was illustrated. The intensity ratio of CN/NH had a greater sensitivity to the equivalence ratio than did that of CN/CH, and the local equivalence ratio could be obtained with high resolution by measuring the local intensity ratios of CN/NH. Moreover, a spark-plug sensor with an optical fiber was developed for application in spark-ignition engines. The atomic emission intensity during the breakdown and arc phases of spark discharge could be obtained using the fiber-optic spark-plug sensor. The H(alpha)/O intensity showed better linearity than the CN/NH intensity ratio in lean mixtures. The results presented here confirm the use of SIBS as a diagnostic tool for spark-ignition engines. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.sab.2009.07.016

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

This study investigated the effect of hydrogen content in producer gas on the performance and exhaust emissions of a supercharged producer gas-diesel dual-fuel engine. Two types of producer gases were used in this study, one with low hydrogen content (H(2) = 13.7%) and the other with high hydrogen content (H(2) = 20%). The engine was tested for use as a co-generation engine, so power output while maintaining a reasonable thermal efficiency was important. Experiments were carried out at a constant injection pressure and injection quantity for different fuel-air equivalence ratios and at various injection timings. The experimental strategy was to optimize the injection timing to maximize engine power at different fuel-air equivalence ratios without knocking and within the limit of the maximum cylinder pressure. Two-stage combustion was obtained; this is an indicator of maximum power output conditions and a precursor of knocking combustion. Better combustion, engine performance, and exhaust emissions (except NO.) were obtained with the high H(2)-content producer gas than with the low H(2)-content producer gas, especially under leaner conditions. Moreover, a broader window of fuel-air equivalence ratio was found with highest thermal efficiencies for the high H(2)-content producer gas. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2009.07.056

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Visualizations of auto-ignition inside the end-gas region due to flame propagation and pressure waves that occur during knocking were carried out in a hydrogen spark-ignition engine using a high-speed camera. Our results demonstrated that auto-ignition in an endgas region that was compressed by the propagating flame front could be visualized using the high-speed color camera. A large amount of unburned mixture caused by the auto-ignited kernel explosion generated the strong pressure waves. Strong pressure wave oscillations induced by the initial auto-ignition could be visualized using a video camera with a speed of 250 kframes/s. The auto-ignition and pressure waves caused the thermal boundary layer to breakdown near the cylinder wall and piston head, therefore combustion of the lubricant oil grease was visible inside burned gas region. This auto-ignition and pressure waves may result in damage to the cylinder wall and piston head during engine knocking. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved

DOI： 10.1016/j.ijhydene.2009.01.091

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE INC  

Images and emission spectra of sparks produced by laser-induced breakdown of methane and propane air mixtures were investigated with a high degree of spatial and temporal resolution. The laser-induced breakdown was generated by focusing a 532-nm nanosecond pulse from a Q-switched Nd:YAG laser. The data were collected using an intensified high-speed camera and a single/multi-fiber Cassegrain optics system coupled to an ICCD spectrometer. Emission spectra of OH*, CN*, CH*, and C-2* radicals were also collected using spectra boxes. The results provided information about the different stages of the laser-induced breakdown, with a specific focus on the transition from a flame kernel to a self-sustaining flame. The plasma shape and emission spectrum were very reproducible. The differences in the size of the flame kernel and the evolution of the radical emissions were analyzed for mixtures that fired or misfired. The impact of the level of radicals in the flame kernel was a critical parameter for the firing process, starting around 1 mu s after the laser-induced breakdown. The transition from plasma cooling to the classical chemical reactions in the combustion zone was analyzed.
Even though the flame kernel size was directly linked to the spark energy, this was not a key parameter toward evolution to a self-sustaining flame. The Taylor blast wave theory was used to plot the location of the shock based on the evolution of the flame kernel size. The location was calculated using a laser-supported detonation model. A very good correlation was observed with the hot gas ignition process. Our results allowed us to obtain information about the process leading to firing or misfiring for similar environments, resulting in a better understanding of the laser breakdown phenomena and the means of utilizing this technique in an industrial context. (C) 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

DOI： 10.1016/j.combustflame.2008.09.013

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

This paper describes laser ignition process in a laminar premixed mixture of propane and air. The plasma was generated by focusing a second harmonic and several-nanosecond pulse emitted from a Q-switched Nd : YAG laser. Minimum ignition energy (MIE) was measured in different equivalence ratio. The growth process in the plasma and the hot kernel (flame kernel) around the MIE were observed using high-speed schlieren photography and a multi-fiber coupled to an ICCD spectrometer. The kernel size, the kernel expansion velocity and the emission spectrum history form the plasma and the kernel were determined under the ignition case and misfire case. Further, temperature of the plasma and the kernel were determined from the CN molecular spectra by comparing experimental and simulated (LIFBASE) spectra. The main results of this study are as follows : (1) In laser ignition method, combustion reaction begins through the cooling process in which the ion recombines to the atom, furthermore the atom recombines to the molecular after breakdown. (2) By analyzing the CH emission intensity history, it was considered that combustion reaction occurs confirmed about 100 μs after laser pulse. (3) The temperature of the plasma and the kernel decrease with time and there were almost no difference between fire and misfire. (4) The minimum ignition energy is the smallest near the stoichiometric mixture.

DOI： 10.1299/kikaib.74.1633

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Images and emission spectra of sparks produced by laser-induced breakdown in air were investigated with a high degree of spatial and temporal resolution. The laser-induced breakdown was generated by focusing a 532-nm nanosecond pulse from a Q-switched Nd:YAG laser. The data were collected using a framing intensified charged coupled device (CCD) camera and a multi-fiber Cassegrain optics system coupled to an intensified CCD spectrometer. The results provided information about the different stages of laser-induced breakdown. The plasma shape and emission spectrum were very reproducible. Different ionization levels in the plasma kernels, which were observed using the high spatial resolution of the multi-fiber Cassegrain optics system, occurred during the plasma formation and cooling and at different locations within the plasma. This was due mainly to the thickness of the plasma relative to the laser wavelength, which created different ionization levels and energy absorption rates throughout. These observations were correlated with the plasma visualizations obtained with the framing ICCD camera. The plasma emission analysis permitted us to study the temperature evolution along the plasma during the laser-induced breakdown process. The analysis demonstrated the validity of a laser-supported wave model during the first stages of laser-induced breakdown and illustrated the weak dependence of the plasma temperature on the input energy.

DOI： 10.1007/s00340-006-2531-4

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE INC  

Cycle-resolved measurements of the fuel concentration near a spark plug in a commercial rotary engine were performed. An in situ laser infrared (IR) absorption method was developed using a spark plug sensor and a 3.392-mu m He-Ne laser as the light source. This wavelength coincided with the absorption line of hydrocarbons. The newly developed IR spark plug sensor had a higher signal-to-noise ratio than its previous version due to the optimization of its quartz lens and two optical fibers. The new sensor provided quantitative cycle-resolved fuel concentration measurements around the spark plug with a high temporal resolution. At lean preset air/fuel (A/F) ratios, fuel was mixed with the surrounding air gradually by the rotor motion in the plug hole of the rotary engine. Strong mixture inhomogeneities were measured during the compression stroke; the magnitude of these inhomogeneities decreased throughout the compression stroke. Cycle-resolved measurements were made to investigate the effects of the fuel concentration near the spark plug on the combustion characteristics of the commercial rotary engine. There was a strong correlation between the fuel concentration measured with the spark plug sensor and the combustion characteristics during the initial combustion period, which occurred faster when conditions were slightly richer than stoichiometric near the spark plug. The indicated mean effective pressure (IMEP) was slightly related to the A/F ratio near the spark plug. It was possible to measure the cycle-resolved A/F ratio near the spark plug and investigate its cycle-to-cycle fluctuations to achieve stable operation using the newly developed spark plug sensor. (c) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

DOI： 10.1016/j.proci.2006.08.088

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Pyrolysis gas produced from woody and waste biomass is considered as one of very important fuels to establish a sustainable society. In this study, asupercharged single cylinder gas engine with micro pilot ignition by gas oil was used. This ignition system has an advantage of large energy source, long period for ignition and stable ignition compared to the spark ignition system. Four types of artificial pyrolysis gases that were compressed into high pressure vessels were used. Compositions of these gases were H_2 , CO, CO_2 , CH_4 and N_2. Combustion was visualized by using a high-speed color video camera from the bottom of the quartz piston. The pressure history was analyzed to obtain the rate of heat release in order to investigate combustion characteristics. Exhaust emissions of NO_x, HC, CO and smoke were measured. Many ignition kernels produced by the iginition of gas oil initiate flame propagation of gas/air mixture and then flames move toward the wall of cylinder. Effects of injection timing, gas composition and equivalence ratio on engine performance were studied.

DOI： 10.1299/kikaib.73.1337

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE INC  

In this study, auto-ignition of end-gas due to flame propagation and intensity oscillations caused by shockwaves that occur during knocking combustion were visualized in a compression-expansion engine using a high-speed video camera. Chemical luminescence emissions of the end-gas were detected to analyze the chemical reactions caused by the auto-ignition. Four main conclusions were drawn from this study. When the end-gas region was compressed due to the propagating flame front, auto-ignited kernels appeared near a negative curvature of the flame front. This negative curvature was related to low-temperature chemistry. The large amount of unburned mixture generated a strong pressure wave caused by the auto-ignited kernels explosion. Visualized images of a regular propagating flame front and auto-ignited kernels confirmed that the knocking intensity had a strong relationship with the mass fraction of the unburned mixture. Oscillations of OH* radicals were synchronized with the in-cylinder pressure oscillations, which were produced due to the resulting shockwave. Before auto-ignition of the end-gas occurred, weak OH* radicals and very weak HCHO* radicals appeared in the end-gas region due to low-temperature chemistry. The OH* radicals played an important role in the low-temperature kinetic reactions. This confirms low-temperature chemical reaction of auto-ignited kernel in the end gas region. OH* radicals are a good indicator of the transition from low-temperature chemistry to high-temperature auto-ignition. (c) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

DOI： 10.1016/j.proci.2006.07.210

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Language：Japanese   Publisher：The Japan Institute of Marine Engineering  

Residual low-grade fuels are often used for marine diesel engines for reasons of economy. Some marine engines have been damaged due to the difficulty of combustion control of such fuels. Many factors affect scuffing of the piston ring and cylinder liner. Because of the complexity and difficulties, however, no one can predict scuffing. Problems have to be solved one by one. This study focuses on scuffing that is caused by the fuel itself. A spray flame was observed with a high-speed video camera in a constant volume vessel, in which ambient pressure and temperature were controlled. A previous study found that after-burning and long ignition delay were problems, so this analysis focused on combustion phenomena after the end of injection. A function of the period from the end of injec-tion till quenching of the flame and of the flame length at quench showed good correlation with the degree of scuffing damage. These two parameters are more valuable for predicting scuffing than are other methods before bunkering fuel in the ship.

DOI： 10.5988/jime.39.250

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Language：English   Publisher：Springer International Publishing  

Very fast visualization of fuel injection and spray impingement on the wall, the laser ignition process, and auto-ignition of the end-gas region due to flame propagation during the engine knock cycle was demonstrated using an ultra-high-speed camera for a detailed understanding of the combustion process inside an internal combustion (IC) engine. The combustion process of an IC engine is complex, involving several thermal fluid phenomena. The high-speed video camera was an essential tool for visualizing and recording these high-speed phenomena. When more magnified images are needed, the ultra-high-speed camera and a long-distance microscope with a Barlow lens were used. Here, high-speed visualization techniques were shown to understand the combustion process inside an IC engine.

DOI： 10.1007/978-3-319-61491-5_12

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Copyright © 2017 by the Japan Society of Mechanical Engineers. The purpose of this study is to simulate the process from spray injection to spray combustion in a rapid compression machine (RCM) more precisely. Spray behavior and spray combustion were simulated by Generalized Tank and Tube (GTT) code which is based on KIVA code. First, the model coefficients of modified wave break-up model for liquid droplet break-up were considered using experimental results of droplet diameter and velocity obtained using a laser 2-focus velocimeter (L2F). Calculation results of spray tip penetration under atmospheric conditions were good agreement with experimental from the visualization of isothermal spray under higher injection pressure conditions. Second, multidimensional CFD simulations of diesel spray combustion using the reduced chemical kinetics were carried out under RCM experimental conditions with 900 K of ambient temperature and 4.1 MPa of ambient pressure. The modelled results were validated by comparing predictions against corresponding experimental results in RCM. The predicted and measured in-cylinder pressure were in good agreement. Ignition process of diesel spray combustion of free spray in RCM were discussed with spray break-up phenomena, entrainment structure of higher injection pressure, and OH radical formation of diesel spray combustion.

DOI： 10.1299/jmsesdm.2017.9.B103

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Language：English   Publisher：SAE International  

A chemical kinetics and computational fluid-dynamics (CFD) analysis was performed to evaluate the combustion of syngas derived from biomass and coke-oven solid feedstock in a micro-pilot ignited supercharged dual-fuel engine under lean conditions. For this analysis, a reduced syngas chemical kinetics mechanism was constructed and validated by comparing the ignition delay and laminar flame speed data with those obtained from experiments and other detail chemical kinetics mechanisms available in the literature. The reaction sensitivity analysis was conducted for ignition delay at elevated pressures in order to identify important chemical reactions that govern the combustion process. We have confirmed the statements of other authors that HO2+OH=H2O+O2, H2O2+M=OH+OH+M and H2O2+H=H2+HO2 reactions showed very high sensitivity during high-pressure ignition delay times and had considerable uncertainty. The chemical kinetics of NOx formation was analyzed for H2/CO/CO2/CH4 syngas mixtures by using counter flow burner and premixed laminar flame speed reactor. The new mechanism showed a very good agreement with experimental measurements and accurately reproduced the effect of pressure, temperature and equivalence ratio on NOx formation. In order to identify the species important for NOx formation, a sensitivity analysis was conducted for pressures 4 bar, 10 bar and 16 bar and preheat temperature 300 K. The results show that the NOx formation is driven mostly by hydrogen based species while other species, such as N2, CO2 and CH4, have also important effects on combustion. Finally, the new mechanism was used in a multidimensional CFD simulation to predict the combustion of syngas in a micro-pilot-ignited supercharged dual-fuel engine and results were compared with experiments. The mechanism showed the closest prediction of the in-cylinder pressure and the rate of heat release (ROHR).

DOI： 10.4271/2017-24-0027

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Bio-gas as an internal combustion (I.C.) engine fuel has many advantages such as cheaper fuel cost, low emission levels and especially the neutral recirculation loop of carbon dioxide, which is one of the principal factors in global warming. In this study, positive potentialities of bio-gas were investigated using a micro co-generation engine. The mixing ratio of methane (CH4) and carbon dioxide (CO2) was changed to simulate various types of bio-gases. Intake air and fuel flow rates were controlled to change the equivalence ratio. The engine load condition could be changed with the electric output power used. Base on the result, the higher CO2 content rate slowed down the engine speed in the same load condition and the combustion speed generally decreased under the same load condition with maintaining the engine speed. However thermal efficiency increased with lean burn conditions and NOX emission decreased with higher CO2 mixing rates.

DOI： 10.4271/2015-01-1946

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A single cylinder, supercharged dual fuel gas engine with micro-pilot fuel injection is operated using methane only and methane-hydrogen mixtures. Methane only experiments were performed at various equivalence ratios and equivalence ratio of 0.56 is decided as the optimum operating condition based on engine performance, exhaust emissions and operation stability. Methane-hydrogen experiments were performed at equivalence ratio of 0.56 and 2.6 kJ/cycle energy supply rate. Results show that indicated mean effective pressure is maintained regardless of hydrogen content of the gaseous fuel while thermal efficiency is improved and presence of hydrogen reduces cyclic variations. Increasing the fraction of hydrogen in the fuel mixture replaces hydrocarbon fuels and reduces carbon monoxide and hydrocarbon emissions. Mixtures with higher hydrogen content undergo faster heat release from flame propagation, approach knocking limit faster and are less knock resistant. 40% methane - 60% hydrogen mixture is prone to premature autoignition and superknocking, and is the critical concentration limit for methane-hydrogen mixtures.

DOI： 10.4271/2015-01-1792

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

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© OSA 2015. Laser ignition of wet ethanol was carried out at equivalence ratio of 0.8. Additions of water in ethanol up to 20% (v/v) accelerated the combustion rate with shorter laser ignition delay compared to dehydrated ethanol.

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DOI： 10.20619/jcombsj.57.180_106

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In this study, simultaneous measurements of hydrocarbon fuel and carbon dioxide (CO_2) concentrations around a spark plug in the homogeneous-charge spark-ignition and the direct-injection spark-ignition engine by a spark plug sensor using infrared absorption technique were carried out. The new simultaneous measuring system including four optical fibers in an M14 spark plug was developed. It was possible that the simultaneous measurement of CO_2 and fuel concentrations in the homogeneous-charge spark-ignition combustion with methane-air or propane-air mixture. Behavior of initial flame kernel around the spark plug can be understood using hydrocarbon fuel and CO_2 concentrations around a spark plug.

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The purpose of this study was to characterize the air/fuel ratio (AFR) of turbulent premixed flames in a spark-ignition (SI) engine. We developed a spark plug sensor with an optical fiber to detect the chemiluminescence spectra, specifically the intensity of the spectral lines related to OH*, CH*, and C2* free radicals. The sensor was composed of a sapphire window and optical fiber and is applicable to automobile SI engines. Measurements of the chemiluminescence intensity from OH*, CH*, and C2* radicals were obtained in turbulent premixed flames with a propane-air mixture for different AFRs in a compression-expansion machine (CEM). The performance of the spark plug sensor was compared with a Cassegrain reflector using an intensified charge-coupled device. The results showed good agreement with measurements obtained using the Cassegrain reflector. The spark plug sensor was shown to be useful for measuring chemiluminescence of turbulent premixed flames in an SI engine. Additionally, the performance of the sensor was evaluated using a high-speed camera, and the chemiluminescence intensity was shown to be related to the time-resolved optical images. Copyright © 2013 SAE International and Copyright © 2013 KSAE.

DOI： 10.4271/2013-01-2578

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Hydrogen spark-ignition (SI) engines based on direct-injection (DI) have been investigated because of their potential for high thermal efficiency and solving the problems related to knocking, backfiring, and pre-ignition. Wide range flammability limits in hydrogen engine enable smooth engine operation for a very lean mixture with low NOX. However, a too lean mixture may increase ignition delay and causes severe cyclic variations. There is a possibility that the turbulence occurred during injection of fuel surround the spark plug in the combustion chamber is major contributor to this phenomenon. To overcome this problem, a better understanding of the spark discharge and spark ignition during transient hydrogen jet is necessary. Therefore, it is very important to study an effect of local equivalence ratio and behavior of spark discharge in SI engine. This paper describes a mixing process of hydrogen jet using spark-induced breakdown spectroscopy (SIBS) in a constant volume vessel. Spark discharge fluctuation images was visualized by high speed camera with the concentration measurement simultaneously. The SIBS sensor was developed from a commercial spark plug with an optical fiber embedded in the spark plug. This technique was used to detect the component of samples using the light emitted by spark-induced plasma. Spectrally resolved emission of plasma generated by the SIBS sensor was detected simultaneously by spectrometer. In this study, the strongest intensity peak of Hα(656nm) and N(501) was chosen to measure the local concentration. Comparing the intensity peaks of atomic emissions from hydrogen and nitrogen gives local hydrogen concentration in the measured volume. Copyright © 2013 SAE International and Copyright © 2013 KSAE.

DOI： 10.4271/2013-01-2526

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The spectral analysis of chemiluminescence of a PCCI diesel engine operating with moderately early injection timing was carried out in a single cylinder test engine. Investigations were conducted through direct visualization of the combustion phenomena with spectroscopic measurement of the intermediate species using a spectrometer coupled to ICCD camera. In order to understand the chemical kinetics of auto-ignition and combustion mechanism in PCCI engine, the spectral analysis of chemiluminescence was carried out. The following intermediate species were identified; OH*, CH*, CO-O recombination and formaldehyde (CH2O) which marked the different combustion phases. Formaldehyde was detected in the low temperature oxidation (LTO) region and isolated clearly by high spectral resolution. The OH* radicals marked the regions with premixed fuel-air mixtures and high temperature oxidation (HTO) region. CH* radicals were noted to mark well the fuel-rich region within the piston cavity after fuel impingement on the Derby hat wall. Soot formation arising from the fuel impingement on the Derby hat wall was oxidized in the late combustion phase. High temperature indicated by high intensity of OH* radicals led to faster oxidation of the soot in the late combustion phase. Copyright © 2012 by the Japan Society of Mechanical Engineers.

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Laser interferometry system was developed to measure unsteady gas temperature. A 16-element photo-diode array was used as the system to detect moving direction of interference fringe more sensitively. Laser interferometry has advantage of nonintrusiveness and high-response. These advantages can improve weak point of general method such as thermistor and thermocouple. In this study, unsteady air temperature was measured by using developed system. Compared with K-type thermocouple of which wire diameter is 0.014mm, this system showed a good response. Because of high response, this system is expected to measure unsteady gas temperature in industrial field.

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Hydrogen spark-ignition (SI) engines based on direct-injection (DI) promise significant advantages in terms of thermal efficiency and power output, as well as a means of overcoming problems related to knocking, backfiring, and pre-ignition. In a DI hydrogen engine, the fuel/air mixture is formed by injecting a jet of hydrogen into the air inside the combustion chamber. An Ar-ion laser beam was used as a light source to visualize the hydrogen jet in a constant-volume chamber. This allowed us to study the structure of the jet in addition to other physical processes resulting from hydrogen gas injection. Combustion experiments were conducted in a single-cylinder SI optical research engine equipped with a DI system to detect the early kernel growth assisted by the spark, as well as flame propagation. Various equivalence ratios and fuel injection timings were analyzed to identify the effects on combustion. © Copyright 2011 Society of Automotive Engineers of Japan, Inc. and SAE International.

DOI： 10.4271/2011-01-2003

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Effects of injection parameters on combustion and emission characteristics of diesel PCCI engine operating on optical and test engine was investigated. PCCI combustion was achieved through slightly narrow included angle injector, low compression ratio coupled with exhaust gas recirculation. Analysis based on diesel spray evolution, combustion process visualization and analysis was carried out. Spray penetration was evaluated and related to the exhaust emissions. Advancing the injection timing and EGR extended the ignition delay, decreased NOx emissions and increased HC, smoke and CO emissions. Higher injection pressure led to low emissions of NOx, smoke, HC and comparable CO. Optimum spray targeting position for minimum emission was identified. Impingement on the piston surface led to deterioration of emissions and increased fuel consumption while spray targeting the upper edge of Derby hat wall showed improvement in emission and engine performance. © Copyright 2011 Society of Automotive Engineers of Japan, Inc. and SAE International.

DOI： 10.4271/2011-01-1769

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The objective of this study is to investigate the performance and emissions in a pilot-ignited supercharged dual-fuel engine, fueled with different types of gaseous fuels under various equivalence ratios. It is found that if certain operating conditions are maintained, conventional dual-fuel engine combustion mode can be transformed to the combustion mode with the two-stage heat release. This mode of combustion was called the PREMIER (PREmixed Mixture Ignition in the End-gas Region) combustion. During PREMIER combustion, initially, the combustion progresses as the premixed flame propagation and then, due to the mixture autoignition in the end-gas region, ahead of the propagating flame front, the transition occurs with the rapid increase in the heat release rate. © Copyright 2011 Society of Automotive Engineers of Japan, Inc. and SAE International.

DOI： 10.4271/2011-01-1764

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DOI： 10.20619/jcombsj.52.159_17

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This study investigated the effect of injection pressure and injection quantity for pilot fuel on engine performance and exhaust emissions of a supercharged producer gas-diesel dual fuel engine. Injection pressure of 80 MPa with the injection quantity of 3 mg/cycle showed the best results. Effect of hydrogen (H_2) content in producer gas on engine performance and emissions is also investigated with two types of producer gases with varying H_2 content with the optimum injection pressure-quantity condition. Experimental strategy was to optimize the injection timing for the maximization of engine power at different fuel-air equivalence ratios without knocking and within the limit of maximum cylinder pressure. Better combustion, engine performance and exhaust emissions (except NOx) are obtained with the high H_2 content producer gas than that with standard producer gas, especially at leaner conditions. Moreover, a broader window of equivalence ratio is found with highest thermal efficiencies with the high H_2 content producer gas.

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DOI： 10.1299/jsmemecjsm.2009.9.0_181

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In this study, fuel concentration measurements in a spark-ignition (SI) engine with ethanol blended gasoline were carried out using an optical sensor installed in the spark plug with laser infrared absorption technique. The spark plug sensor for in-situ fuel concentration measurement was applied to a port injected SI engine. The molar absorption coefficients of ethanol blended gasoline were determined for various pressures and temperatures in advance using a constant volume vessel with electric heating system. Ethanol blended gasoline with high volumetric ratios shows lower molar absorption coefficients due to lower molar absorption coefficients of ethanol. The molar absorption coefficients of ethanol blended gasoline can be estimated by considering the molar fraction of each component. Mixture formation processes of ethanol blended gasoline were investigated using spark-plug sensor installed in a spark plug in a port-injected SI engine with changing the fuel injection timing in an intake port. Delaying injection of ethanol blended gasoline caused a leaner fuel concentration around the spark plug and cycle-to-cycle fluctuation of combustion. Copyright © 2009 SAE International.

DOI： 10.4271/2009-01-1957

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This study investigated the effect of some pilot fuel injection parameters, like injection timing, injection pressure and injection quantity on engine performance and exhaust emissions of a supercharged producer gas-diesel dual fuel engine. The engine has been tested to be used as a co-generation engine and its power output is an important matter. Experiments have been done to optimize the injection timing, injection pressure and injection quantity for the maximization of engine power. At constant injection pressures, there is an optimum amount of pilot injection quantity for that maximum engine power is developed without knocking and within the limit of maximum cylinder pressure. Above or below of that amount engine power is decreased. Higher injection pressures generally show better results than lower ones. However, good results can also be obtained with lower injection pressure, if maximum power timings can be selected. Two-stage combustion is obtained as a mentionable fact which is an indicator of maximum power output conditions as well as a precursor of knocking combustion. Smoke is found almost zero throughout the experiments and hydrocarbons (HC) are very low. However, carbon monoxide (CO) level at all experimental conditions is very high. Nitrogen oxides (NOx) at maximum power conditions are also very high. These need to be reduced. Copyright © 2009 SAE International.

DOI： 10.4271/2009-01-1848

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The combustion and exhaust emissions characteristics of a supercharged dual-fuel natural gas engine with a single cylinder were analyzed. We focused on EGR (Exhaust Gas Recirculation) to achieve higher thermal efficiency and lower exhaust emissions. The combustion of diesel fuel (gas oil) as ignition sources was visualized using a high-speed video camera from the bottom of a quartz piston. The luminous intensity and flame decreased as the EGR rate increased. Furthermore, the ignition delay became longer due to the EGR. Characteristics of the combustion and exhaust emissions were investigated with changing EGR rates under supercharged conditions. The indicated mean effective pressure and thermal efficiency decreased with increasing EGR rate. In addition, NOx emissions decreased due to the EGR. In this study two-stage combustion was observed. When two-stage combustion occurred, it was supposed that auto-ignition of compressed natural gas and air mixture occurred during the flame development. However, knocking did not occur. Two-stage combustion occurred under the condition of low EGR rate and advanced injection timing. The indicated mean effective pressure and thermal efficiency increased, during two-stage combustion
however, NOx emissions also increased by a large amount compared to normal combustion. High indicated mean effective pressure, high thermal efficiency, and low NOx emissions were achieved just before the occurrence of two-stage combustion by changing EGR rate and injection timing of diesel fuel. Copyright © 2009 SAE International.

DOI： 10.4271/2009-01-1832

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The present paper reports an experimental investigation of the effect of nozzle geometry of port fuel injector PFI on exit flow velocity, the stability of primary spray behavior and spray droplet size. Several types of PFI with were tested. The investigation of exit flow velocity and stability (wavelength) of spray structure was performed using an ultra high-speed video camera (max. camera speed 1Mfps) with a long-distance microscope (whole image). The visualized experiments were carried out in a closed chamber at the atmospheric pressure. With back-lighting, the time-series images of the spray behavior were obtained. Using ultra high-speed camera with long-distance microscope and Barlow lens, droplet diameter could be visualized with high temporal resolution (magnified image). Experimental results of average exit velocity compared with NOZZLE FLOW model where experimental results of stability and droplet diameter compared with KH-RT breakup model. Experimental investigation showed that exit velocity, droplet diameter and stability (wavelength) influence by nozzle geometry. Copyright © 2008 by the Japan Society of Mechanical Engineers.

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The spray from a multi-hole injector applied to direct injection spark ignition (DISI) engine was investigated. The spray has been injected into a constant volume chamber and has been visualized with a high speed video camera with a long distance microscope and quantified in terms of droplet velocity and diameter with HiDense PDA system. HiDense PDA system permits accurate measurements in spray with extremely high particle concentrations, and it is the only PDA system available that provide high quality measurements in the core region of the spray cone. The spray close to the nozzle has been investigated. Also the spray at the center axis far from the nozzle has been investigated at different injection pressure. PDA data have been processed by using a time-dividing method which divides the spray information into four distinct periods (F, C, R and T). As a result it was found that large particles ∼ (85 μm) which are injected at high speed ∼ (90 m/s) in the earliest stage lose their velocity rapidly due to breakup into smaller droplets and are overtaken by smaller but slower particles which are emitted during a later stage. The results also show that within the measured range the effect of injection pressure on droplet size was rather small. Copyright © 2008 by the Japan Society of Mechanical Engineers.

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In this report, fuel spray, especially engine application, and measurement techniques for fuel injection characteristics, such as break-up of liquid column, spray angle, penetration length, followability of droplets, droplet dispersion, entrainment vortex structure and so on, are explained. Microscopic visualization of liquid column break-up process in a gasoline PFI injector and simultaneous measurements of droplet diameter and velocity using phase Doppler anemometer (PDA/PDPA) are introduced as examples of measurement techniques. Obtained knowledge of spray and atomization characteristics using these techniques are mentioned in the case of unsteady spray from a gasoline injector.

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DOI： 10.11426/nagare1982.27.303

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© 2007 Combustion Institute. All Rights Reserved. This paper describes the application of a spark plug sensor using a 3.392 μm infrared absorption technique to quantify the instantaneous gasoline concentration near the spark plug inside the engine cylinder. The mixture formation process near the spark plug in a port-injected spark-ignition (SI) engine was examined for different fuel injection timings, and determined that when the injection timing was delayed, a rich mixture remained near the top of the combustion chamber. Cyclic variations of fuel concentration at the spark timing were investigated.

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Non-intrusive measurement of transient unburned gas temperatures was developed with a fiber-optic heterodyne interferometry system. Using the value of the Gladstone-Dale constant for DME gas and combustion pressure we can calculate the in-cylinder temperature inside unburned and burned region. In this experimental study, it was performed to set up a fiber-optic heterodyne interferometry technique to measure the temperature before and behind the combustion region in a DME-HCCI engine. At first, measured temperature was almost the same as the temperature history assuming that the process that changes of the unburned and the burned are polytropic. In addition, we measured the temperature after combustion which of condition was burned gas with DME-HCCI combustion. The developed heterodyne interferometry used the spark-plug-in fiber-optic sensor has a good feasibility to measure the unburned and burned temperature history. Copyright © 2007 Society of Automotive Engineers of Japan, Inc.

DOI： 10.4271/2007-01-1848

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In this study, residual gas fraction measurements in a spark-ignition engine were carried out using an optical sensor installed in the spark plug with infrared absorption method. The residual gas fraction inside engine cylinder is proportional to the CO2 concentration. Infrared absorption method was applied and an infrared lamp and optical filter (center wavelength: around 4.3 μm) that coincides with the absorption lines of CO2 was used as a light source.The molar absorption coefficient of CO2 is discussed and compared to results in the HITRAN database. The effect of water vapor absorption doesn't affect the absorption of CO2. The absorption characteristics of CO2 were determined in advance using a constant volume vessel. Molar absorption coefficient depends on the CO2 concentration and ambient pressure and temperature, and wavelength of absorption line. Further experiments should be carried out for the quantitative measurements of CO2 concentration using infrared lamp and band-pass filter. The spark plug sensor for in-situ CO2 concentration measurement was applied to a compression-expansion machine and also to a port injected SI engine. It was possible to qualify the CO2 concentration inside residual gas during the compression stroke using the developed optical system with new spark plug sensor both in compression-expansion machine and commercial spark-ignition engine. Copyright © 2007 Society of Automotive Engineers of Japan, Inc.

DOI： 10.4271/2007-01-1849

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It is very important to measure fluid temperature in research and industrial fields. However, there are no devices with high-response measurement. In this study, a sensor system is proposed to measure the temperature with very high response using interferometry. The sensor for temperature measurement utilizes the difference in measurement length between two laser beams. Both are the test beams, and there is no reference beam. The two beams pass mostly through closely arranged paths; therefore, the effect of mechanical vibration on the two test beams is expected to be very small. The laser beam was introduced through a selfoc micro lens (SML) into a polarization-maintaining fiber connected with a sensor part. The beam emitted from another SML was divided into two. Both beams enter a quartz block and are reflected at the corner to change direction by an angle of a quarter pai radian. They then pass through the test section although the lengths of the two beams are different in the measurement region. This sensor was installed on a side wall of a vessel. Water was poured into the vessel and stirred with a hot magnetic stirrer. The temperature near the sensor was also measured with a thermocouple as a reference. This paper focuses on the confirmation and evaluation of this system of temperature measurement. When the direction of the fringe shift with two photo-detectors was judged, the direction of the temperature could be distinguished. One feature of this sensor is that it minimizes the effect of the thermal boundary layer. If the condition of the fluid near the test section is uniform, both beams have almost the same boundary layers. Then, both thermal boundary layers are expected to be cancelled because the length of the test section is the difference between both beams. As a result, it was confirmed that this sensor system is useful for detecting changes in water temperature.

DOI： 10.1115/HT2007-32022

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Spray characteristics were investigated to determine the optimum aerosol spray for insecticides while considering volatile organic carbon (VOC) reduction. Our ultimate goal is to improve the efficiency of killing insects while using less aerosol spray, which contains chemicals, oil, and dimethyl ether (DME). Most of the oil and propellant fail to reach the target, and fall to the ground. The propellant is used to break droplets into smaller droplets and to carry them to the target. Most of the propellant's energy is used for carrying these droplets, although the remaining droplets are very small compared to those produced at the nozzle. We investigated the droplet characteristics over the entire distance from the nozzle to the target. Here, we tested different nozzle dimensions and compared single- and double-hole nozzles. We measured the spray characteristics near the nozzle to evaluate the droplet-forming process by examining droplet separation, agglomeration, collision, and size to elucidate the spray behavior and determine the dominant factors involved in designing and developing a nozzle for spraying insecticides most effectively. The key factor for developing the optimum nozzle for spraying insecticides is not the number of holes or nozzle diameter, but the agglomeration process and the amount at the target distance. The key to developing a system that decreases VOC dramatically is how the droplets are generated at the nozzle. Droplet diameter and velocity when exiting the nozzle need to be understood quantitatively and controlled; the most important considerations are to maximize spray agglomeration, in order to deliver droplets with an effective diameter to the target, and to reduce the number of oversized droplets failing to reach the target.

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The droplet characteristics of unsteady fuel spray formed by multi-hole injector used in direct injection gasoline engine was investigated. In order to understand the detail structure of transient spray, a phase Doppler anemometer was used. The traverse system of the vessel was designed to obtain two-dimensional structure of spray. The laser power at measurement volume was optimized in order to detect relative smaller droplets. It is necessary to evaluate the effect of laser power of measurement volume on detection limit of smaller droplets under 10 μm. Phase locking method was used to analyze ensemble mean value of axial/radial droplet velocity, axial/radial slip velocity, relative droplet Reynolds number, and droplet turbulent kinetic energy. As a result, smaller droplets under 10 μm can follow the entrainment vortex at the spray shell. On the other hand, larger droplets over 30 μm have larger velocity to penetrate the entrainment vortex. Intermediate droplets of 15<D≦ 20μm in diameter are criteria for follow/penetration of vortex.

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We investigated laser-induced breakdown in air using a framing intensified charged coupled device (ICCD) camera and fiber-coupled ICCD spectrometer with Cassegrain optics. Localized breakdown plasma was generated from the laser pulse of a Q-switched Nd:YAG laser with a wavelength of 532 nm, and we obtained the temporal evolution of the air plasma shape, size, and location. During the initial stage, breakdown occurred on the laser side of the focal point due to the absorption of the pulse energy. Then, the breakdown plasma generally propagated in the direction of the laser. The propagation speed of the laserinduced breakdown was estimated to exceed 10 km/s during the initial stage of breakdown. The high spatial resolution of the Cassegrain optics system was used to observe different ionization levels in the breakdown plasma. Continuous background due to ionization appeared during the earliest stage of plasma development. The intensity of this background decreased after 100 ns and the atomic emission spectra of nitrogen (NI, 745 nm), oxygen (OI, 777 and 821 nm) and hydrogen (HI, 655.5 nm) appeared 200 ns after the laser pulse. The plasma temperature could be evaluated using the two-line ratio between the OI emission line intensities. We determined that simultaneous measurement using both the framing ICCD camera and an ICCD spectrometer with Cassegrain optics could be very useful for investigating the breakdown of laser-induced air plasma.

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The local equivalence ratios of CH4/air and C3H 8/air mixtures were measured using a laser-induced breakdown spectroscopy technique with a fiber-coupled ICCD spectrometer with Cassegrain optics. Localized breakdown plasma was generated from the pulse of a Q-switched Nd:YAG laser with a wavelength of 532 nm. This system allowed us to measure laser-induced plasma spectra with high spatial and temporal resolution. The specified intensity ratio and set up equivalence ratios were well correlated and found to be a good indicator in practical measurement. The intensity ratio indicated a remarkable relationship regardless the presence of the flame. For the unburned and burned regions, there were some differences in the change in the intensity ratio, but the calibration slopes were almost similar. It was found that this technique can measure the local equivalence ratio of methane or propane premixed laminar flame regardless a flame. The intensity ratio was not a function of the incident beam intensity or flow rate, which is very acceptable for practical measurement. In this experiment, the relative error was around 5%.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In this study, a new sensor is proposed to determine water temperature. This sensor utilizes the difference in measurement length between two laser beams. Both are the test beams, and there is no reference beam. The two beams pass mostly through equal or closely arranged paths ; therefore, the effect of mechanical vibration on the two test beams is expected to be very small. This sensor was installed on a side wall of a vessel. The temperature near the sensor was also measured with a thermocouple as a reference. The response of the thermocouple was enough to follow the change in water temperature because the speed of temperature is very slow. This paper focuses on the confirmation and evaluation of this system of temperature measurement. The temperature measured with this system agreed well with that measured with a thermocouple. It was confirmed that this sensor system is useful for detecting changes in water temperature.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

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This paper describes the development and application of a spark plug sensor using a 3.392 μm infrared absorption technique to quantify the instantaneous gasoline concentration near the spark plug. We developed an in situ laser infrared absorption method using a spark plug sensor and a 3.392 μm He-Ne laser as the light source
this wavelength coincides with the absorption line of hydrocarbons. First, we established a database of the molar absorption coefficients of premium gasoline at different pressures and temperatures, and determined that the coefficient decreased with increasing pressure above atmospheric pressure. We then demonstrated a procedure for measuring the gasoline concentration accurately using the infrared absorption technique. The history of the molar absorption coefficient of premium gasoline during the experiment was obtained from the established database using measured in-cylinder pressures and temperatures estimated by taking the residual gas into consideration. These values provided instantaneous fuel concentrations in the engine cylinder. We examined the mixture formation process near the spark plug in a port-injected spark-ignition (SI) engine for different fuel injection timings, and determined that when the injection timing was delayed, a rich mixture remained near the top of the combustion chamber. Copyright © 2006 SAE International.

DOI： 10.4271/2006-01-0182

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A small Cassegrain optics sensor was developed to measure local chemiluminescence spectra and the local chemiluminescence intensities of OH*, CH*, and C2* in a four-stroke spark-ignition (SI) engine in order to investigate the propagation characteristics of the turbulent premixed flame. The small Cassegrain optics sensor was an M5 type that could be installed in place of a pressure transducer. The measurements could be used to estimate the flame propagation speed, burning zone thickness, and local air/fuel (A/F) ratio for each cycle. The specifications of the small Cassegrain optics sensor were the same as those used for previous engine measurements. In this paper, measurements were made of several A/F ratios using gasoline to fuel the model engine. The performances of two Cassegrain optics sensors were compared to demonstrate the advantages of the new small sensor by measuring the local chemiluminescence intensities of a turbulent premixed flame in the model engine. The measurements suggested that the small Cassegrain optics sensor is superior to the conventional Cassegrain sensor and can provide stable data for measurements over several hours, which should be sufficient for practical combustion diagnostics. This sensor proved useful for estimating the flame propagation characteristics. In addition, the sensor should be useful for local A/F ratio measurements in an engine cylinder. Copyright © 2005 SAE International.

DOI： 10.4271/2005-01-0645

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A heterodyne interferometry system with a fiber-optic sensor was developed to measure the temperature history of unburned gas in a spark-ignition engine. A polarization-preserving fiber and metal mirror were used as the fiber-optic sensor to deliver the test beam to and from the measurement region. This fiber-optic sensor can be assembled in an engine cylinder head without a lot of improvements of an actual engine. Adjustment system in the sensor was revised to face the distributed index lens with metal mirror. Before the flame arrived at the developed fiber-optic sensor, measured temperature was almost same with the temperature history after the spark, assuming that the process that changes the unburned gas is adiabatic. In situ unburned gas temperature measurements before knocking in a commercially produced SI engine can be carried out using developed fiber-optic heterodyne interferometry system. Although the heterodyne interferometry with the developed fiber-optic sensor provides the mean temperature along the line of sight, the feasibility of our system was sufficient to be applied to temperature history measurement of an unburned gas compressed by flame propagation in an engine cylinder. The developed heterodyne interferometry with fiber-optic sensor has a good feasibility to measure the unburned gas temperature history in the commercially produced spark-ignition engine. Copyright © 2005 SAE International.

DOI： 10.4271/2005-01-0646

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An in-spark-plug flame sensor was developed to measure local chemiluminescence near the spark gap in a practical spark-ignition (SI) engine in order to study the development of the initial flame kernel, flame front structure, transient phenomena, and the correlation between the initial flame kernel structure and cyclic variation in the flame front structure, which influences engine performance directly. The sensor consists of a commercial instrumented spark plug with small Cassegrain optics and an optical fiber. The small Cassegrain optics were developed to measure the local chemiluminescence intensity profile and temporal history of OH*, CH*, and C 2* at the flame front formed in a turbulent premixed flame in an SI engine. A highresolution monochromator with an intensified chargecoupled device (ICCD) and spectroscopy using optical filters and photomultiplier tubes (PMTs) were used to measure the time-series of the three radicals, as well as the in-cylinder pressure. Measurements were made at different engine speeds in an unmodified 223-cc practical SI engine fueled with gasoline. Stable data were obtained over several hours with little noise, and were of the same quality as data from a small M5-type sensor installed instead of a pressure transducer. The relationships between the radical intensities and indicated mean effective pressure (IMEP) were examined and typical cyclic variation was measured at speeds over 7,000 rpm. The behavior of the initial flame was followed from its arrival at the measurement point. The arrival time was faster and IMEP was larger at stoichiometry than under other air/fuel (A/F) conditions. Copyright © 2005 SAE International.

DOI： 10.4271/2005-01-0644

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Language：Japanese   Publisher：一般社団法人日本機械学会  

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An in-spark-plug flame sensor was developed to measure local chemiluminescence near the spark gap in a practical spark-ignition (SI) engine in order to study the development of the initial flame kernel, flame front structure, transient phenomena, and the correlation between the initial flame kernel structure and cyclic variation in the flame front structure, which influences engine performance directly. The sensor consists of a commercial instrumented spark plug with small Cassegrain optics and an optical fiber. The small Cassegrain optics were developed to measure the local chemiluminescence intensity profile and temporal history of OH*, CH*, and C 2* at the flame front formed in a turbulent premixed flame in an SI engine. A highresolution monochromator with an intensified chargecoupled device (ICCD) and spectroscopy using optical filters and photomultiplier tubes (PMTs) were used to measure the time-series of the three radicals, as well as the in-cylinder pressure. Measurements were made at different engine speeds in an unmodified 223-cc practical SI engine fueled with gasoline. Stable data were obtained over several hours with little noise, and were of the same quality as data from a small M5-type sensor installed instead of a pressure transducer. The relationships between the radical intensities and indicated mean effective pressure (IMEP) were examined and typical cyclic variation was measured at speeds over 7,000 rpm. The behavior of the initial flame was followed from its arrival at the measurement point. The arrival time was faster and IMEP was larger at stoichiometry than under other air/fuel (A/F) conditions. Copyright © 2005 SAE International.

DOI： 10.4271/2005-01-0644

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Experimental investigations of fuel breakup very close to nozzle of practical high-pressure swirl injector, which is used in direct injection spark ignition (DISI) engine, were carried out. In DISI engines, fuel is directly injected into cylinder therefore the spray characteristics and mixture formation are of primary importance. Many experimental investigations using several measurement techniques like laser sheet method with high-speed camera, LIF or PDA have been carried out for better understandings of spray and combustion characteristics. However, experimental investigations of atomization process were restricted due to very high-speed and very small region phenomena. Although scale-up models have been used to study the primary spray structure, it is impossible to match Reynolds, Weber, and cavitation numbers and time scales in practical high-pressure swirl injector. Microscopic investigation of primary spray structure of practical swirl injector is needed. On the other hand, numerical simulations have been conducted for better understanding of spray formation process. These researches indicated qualitatively good agreement, but the initial conditions, such as liquid sheet thickness and break-up length, were not accurately since break-up process of the liquid sheet from swirl injector has not been examined. In numerical simulation of spray behavior, a sub-model for atomization phenomena is very important. Therefore the primary atomization process and the break-up process of liquid sheet play an important role. In this research, visualizations of primary spray formation process were demonstrated using a high-speed video camera (maximum speed: Imfps) with a long-distance microscope. Initial state and development of the spray were discussed under the different ambient (back) pressure condition. During the injection period, the length and thickness of the liquid sheet, which is produced from the nozzle exit, were measured using Ar-ion laser sheet and high-speed camera. Moreover, fluctuations of the length and thickness of liquid sheet were discussed. Three main conclusions were drawn from this study. (1) It has been shown that the liquid fuel column without swirl motion was injected as a compact jet at the beginning of the injection. During the injection period, the spray indicates the quasi-steady state mode. (2) Liquid film sheet has a ligament structure. Using Ar-ion laser sheet and high-speed camera, length and thickness of the liquid sheet can be measured. (3) Surface waves of liquid sheet can be recognized. Higher ambient (back) pressure makes shorter wavelength of surface waves of liquid sheet of swirl injector.

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Experimental investigations of fuel breakup very close to nozzle of practical high-pressure swirl injector, which is used in gasoline direct injection (GDI) engine, were carried out. In GDI engines, fuel is directly injected into cylinder therefore the spray characteristics and mixture formation are of primary importance. In this research, visualizations of primary spray formation process were demonstrated using a high-speed video camera (maximum speed: 1Mfps) with a long-distance microscope. Initial state and development of the spray were discussed under the different injection pressure condition. During the injection period, the length and thickness of the liquid sheet, which is produced from the nozzle exit, were measured using Ar-ion laser sheet and high-speed camera. Primary spray structure and behavior of liquid sheet, especially surface wave of liquid sheet, at nozzle exit were discussed using obtained images. Three main conclusions were drawn from this study. (1) It has been shown that the liquid fuel column without swirl motion was injected as a compact jet at the beginning of the injection. During the injection period, the spray indicates the quasi-steady state mode. (2) Liquid film sheet has a ligament structure. Using Ar-ion laser sheet and high-speed camera, length and thickness of the liquid sheet can be measured. Higher injection pressure causes thinner thickness and shorter length of liquid sheet. (3) Surface waves of liquid sheet can be recognized. Higher injection pressure makes larger wavelength of surface waves of liquid sheet of swirl injector. Copyright © 2004 SAE International.

DOI： 10.4271/2004-01-0542

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An infrared absorption method was used to determine the fuel concentration with a 3.392 μm He-Ne laser. The effects of pressure and temperature on the molar absorption coefficients of hydrocarbon fuels were clarified, so that it increased with increasing temperature and decreased with increasing pressure. Molar absorption coefficient of multi-component fuel like gasoline can be estimated using molar absorption coefficient of each component and considering mass balance. By exchanging an ordinary spark-plug for &amp
spark-plug with a developed sensor in which light can pass through mixture in the combustion chamber, successive measurement of fuel concentration was performed in a spark-ignition engine. The effects of liquid droplets, mechanical vibration, and other gas like H2O on measurement accuracy were discussed.

DOI： 10.1299/kikaib.70.518

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A fiber optic system linked to the optical sensor installed in the spark plug, in which light can pass through the combustion chamber, was developed to determine the fuel concentration near the spark-plug successively using an infrared absorption method. A He-Ne laser with a wavelength of 3.392 μm that coincides with the absorption line of hydrocarbons was used as a light source. By exchanging an ordinary spark plug into this spark plug with the optical sensor, sucessive measurement of fuel concentration before the spark timing near the spark-plug was performed in a spark-ignition engine inducted with homogeneously mixed method methane-air. The fuel concentration was determined from law of Lambert-Beer in consideration for the effects of pressure and temperature on molar absorption coefficient of methane.

DOI： 10.1299/kikaib.70.511

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A small flame sensor was developed to measure the local chemiluminescence intensity of OH*, CH* and 2* in a four-stroke spark-ignition engine in order to understand flame front characteristics, flame propagation speed and local air/fuel (A/F) ratios. This sensor was installed where a pressure transducer was located. The dimensions of the sensor were those of the M5 type; the specifications of the developed small Cassegrain optics were the same as those used in previous engine measurements. The measurements were carried out at engine speeds of 600 and 1200 rpm using propane and gasoline fuels with no hardware modification in a 374.7 cc. model engine. Two types of Cassegrain optics were examined to measure local chemiluminescence of the flame in the engine. The small optics developed can provide very stable data for an experiment lasting several hours, which is sufficient to conduct practical combustion diagnostics. The measurements results with propane and gasoline demonstrated that this sensor is little influenced by fuel type, and the flame propagation speed was similar under both conditions. Although the sensor must be calibrated for a particular engine initially, it can measure local A/F and flame parameters in each cycle in practical engines. On-board diagnostics can be performed using this sensor and the flame speed and local equivalence ratio at the flame front can be calculated without modifying the engine hardware. This sensor should prove useful for measuring flame structure and stoichiometry in order to reduce cyclic variation and give the optimum control of each cylinder in practical engines.

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A swirling flow and rich fuel concentration near the center were produced in a vessel by tangentially charging air and fuel injection. Propane was used as fuel. Fuel concentration distribution was measured with laser induced fluorescence (LIF) method using acetone as a tracer. It was confirmed that the center-rich stratified fuel concentration was produced. In order to estimate the pattern of the fuel concentration field, the Gaussian fitting method was applied to the equivalence ratio profile. Fuel distribution history obtained from LIF measurement agreed with the calculation result using axisymmetric diffusion equation. The initial stage of combustion was greatly affected by the fuel concentration distribution in the vicinity of the spark location. The stronger turbulence intensity accelerated combustion and main combustion became shorter under the same fuel distribution conditions.

DOI： 10.1299/kikaib.70.1092

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In this study, a spark plug sensor for in-situ fuel concentration measurement was applied to a port injected lean-burn engine. Laser infrared absorption method was employed and a 3.392 μm He-Ne laser that coincides with the absorption line of hydrocarbons was used as a light source. In this engine, the secondary valve lift height of intake system was controlled to obtain appropriate swirl and tumble flow in order to achieve lean-burn with the characteristics of intake flow. For such in-cylinder stratified mixture distribution, the fuel concentration near the spark plug is very important factor that affects the combustion characteristics. Therefore, the mixture formation process near the spark plug was investigated with changing fuel injection timing. Under the intake stroke, the timing that fuel passed through near the spark plug depended largely on the fuel injection timing. Under the compression stroke, mixture formation process near the spark plug indicated different characteristics with injection timings. As the injection timing was retarded, rich mixture remained near the top of the combustion chamber. Furthermore, the relation between the fuel concentration near the spark plug and the combustion characteristics was discussed. The initial combustion became faster and the coefficient of variation in IMEP became lower as the rich mixture existed near the spark plug. Copyright © 2004 SAE International.

DOI： 10.4271/2004-01-1353

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Language：Japanese   Publisher：日本工業炉協会  

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Language：English   Publisher：IOP PUBLISHING LTD  

An infrared absorption method with a 3.392 mum He-Ne laser was used to determine the hydrocarbon fuel concentration near the spark plug in a spark-ignition engine. Iso-octane was used for the fuel. The pressure and temperature dependence of the molar absorption coefficient was clarified. The molar absorption coefficients of a multi-component fuel such as gasoline were estimated by using the coefficient of each component and considering the mass balance. A sensor was developed and installed in a spark plug, which was substituted in place of an ordinary spark plug in a spark-ignition engine. Light can pass from the sensor through the engine cylinder to measure the fuel concentration. The effects of liquid droplets inside the engine cylinder, mechanical vibrations and other gases such as H2O and CO2 on the measurement accuracy were considered. Four main conclusions were drawn from this study. First, the pressure and temperature effects on the molar absorption coefficient of liquid fuel vapour were determined independently in advance using a constant-volume vessel. The pressure and temperature dependence of the molar absorption coefficient was determined under engine firing conditions. Second, the molar absorption coefficients of a multi-component hydrocarbon fuel such as gasoline were estimated by considering the molar fraction of each component. Third, in situ measurements of the hydrocarbon fuel concentration in an actual engine were obtained using the spark plug sensor and the molar absorption coefficient of iso-octane. The concentration near the spark plug just before ignition was almost in agreement with the mean value that was obtained from the measurement of the flow rate made with a burette, which represented the mean value averaged over many cycles. And fourth, no liquid droplets were observed at near-idling conditions. The effects of other gases, such as CO, CO2 and H2O, can be neglected.

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Homogeneous Charge Compression Ignition (HCCI) combustion with dimethyl ether has been carried out in a single cylinder engine with a transparent piston. The engine was operated at 800 rpm with a wide-open throttle. The intake-premixed mixture was preheated with an electric heater to promote auto-ignition. HCCI combustion with dimethyl ether indicates multi-stage heat releases. Investigations were conducted with visualization of combustion in the cylinder and detailed and temporal spectroscopic measurements using spectrometer. In order to understand reaction mechanism of auto-ignition and combustion mechanism in HCCI engine, spectrum analysis of chemiluminescence was carried out. Three main conclusions were drawn from this study. (1) Spectrum from chemiluminescence at low temperature oxidation was obtained successfully using developed optical fiber probe. (2) Emitting lights from HCHO according to Emeléous's cool flame bands appear at low temperature reaction. (3) During the main heat release, the CO-O recombination spectrum was strong. There was a strong correlation between rate of heat release and the CO-O recombination spectrum. Copyright © 2003 Society of Automotive Engineers of Japan, Inc.

DOI： 10.4271/2003-01-1828

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This study measured the fuel concentration near a spark plug using a laser infrared absorption method. An IR spark plug sensor with a double-pass measurement length was developed. A He-Ne laser with a wavelength of 3.392 μm, which coincides with the absorption line of hydrocarbons, was used as the light source. In order to confirm the measurement accuracy, the concentrations of a methane-air mixture were measured in a compression-expansion engine. Then, the IR spark plug sensor was used for measurements in a 4-stroke spark-ignition engine fuelled with isooctane. The air/fuel ratio measured using this system clearly agreed with the mean air/fuel ratio. Copyright © 2003 SAE International.

DOI： 10.4271/2003-01-1109

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Language：Japanese   Publisher：Japan Society of Mechanical Engineers  

Dual fuel natural gas engines have been studied for the purpose of near future engine. This study focuses on the effect of early injection of light oil and exhaust gas recirculation (EGR) fueled with methane from an inlet pipe on characteristics of combustion and exhaust emissions. The injection timing was changed from TDC to 50 degrees before the TDC. In the early injection timing, smoke was never seen and hydrocarbons were smaller compared with those at the normal injection timing. However, the combustion becomes too early to obtain an appropriate torque when the equivalence ratio increases. Then, moderate nitrogen dilution was very effective to retard the combustion with lower NOx, higher thermal efficiency and almost the same hydrocarbons and carbon monoxide. And it was found that the engine operates even under the condition of stoichiometric mixture.

DOI： 10.1299/kikaib.69.988

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A heterodyne interferometry system with a fiber-optic sensor was developed to measure the temperature history of unburned gas in an engine cylinder. A polarization-preserving fiber and metal mirror were used as the fiber-optic sensor to deliver the test beam to and from the measurement region. This fiber-optic sensor can be assembled in the engine cylinder or the cylinder head without a lot of improvements of an actual engine. The feasibility of our system was sufficient to be applied to temperature history measurement of an unburned gas compressed by flame propagation in an engine cylinder. The resolution of the temperature measurement is approximately 0.7 K, and is dependent on both the sampling clock speed of the A/D converter and the length of the measurement region. Copyright © 2003 Society of Automotive Engineers of Japan, Inc.

DOI： 10.4271/2003-01-1799

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A swirling flow was produced in a vessel by tangentially charging fuel-air mixture or air. Rich fuel concentration was formed near the center of the vessel by fuel injection. Mixture was ignited at the center of the vessel. Various swirling flow field and fuel concentration field were made by changing the mean equivalence ratio in the vessel, the timing of charging mixture and fuel injection. The mean equivalence ratio in the vessel was changed from 0.20 to 0.84. Appropriate mixture stratification enabled initial combustion to be faster than that of homogeneous mixture. Under the lean condition, the combustion efficiency was lower and flame could not propagate in the lean mixture region near the wall as the homogeneity of the mixture became larger. In the case of the slowest swirling condition, initial combustion and initial flame propagation became slower due to rich mixture near the center of the chamber.

DOI： 10.1299/kikaib.69.2531

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Language：English   Publisher：Institute of Physics Publishing  

A fibre optic system was developed to determine the fuel concentration near a spark plug using an infrared absorption method. The system was linked to an optical sensor installed in the spark plug, from which light could pass through the combustion chamber. By using this modified spark plug, successive measurements of the fuel concentration near the spark plug before ignition were performed in a spark-ignition engine burning homogeneously mixed methane-air. The fuel concentration was determined from the Lambert-Beer law by considering the dependence of the methane molar absorption coefficient on pressure and temperature. Three main conclusions were drawn from this study. First, the methane molar absorption coefficient was greater for lower pressures and decreased with increasing temperature and pressure above atmospheric pressure. The temperature and pressure effects were offset by each other, since the temperature effects were positive and the pressure effects were negative. Second, precise time-series data for the local fuel concentration were obtained by considering the in-cylinder pressure and temperature from an estimate of the methane molar absorption coefficient. And third, the measured air/fuel ratio near the spark plug before ignition agreed with the preset value when the developed optical sensor was used under motoring and firing conditions.

DOI： 10.1088/0957-0233/14/8/321

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This paper demonstrates an application of the optical heterodyne interferometry, a laser-based technique for measuring the temperature history of gas in combustion devices, such as internal combustion engines. The technique is based on refractive index measurements using laser interferometry along a line of sight. The temperature history of gas can be determined from the pressure history in the combustion chamber, the gas composition, and the laser interference intensity. A polarization-preserving fiber was used to deliver the test beam to and from the test section to improve the feasibility of the system as a sensor probe. The temperature of the unburned mixture in the end-gas region of a constant volume combustion chamber and in an engine cylinder were measured during flame propagation. The accuracy of the measurement and the feasibility of this system are discussed. The measurement accuracy of our system was sufficient to be applied to temperature history measurement of an unburned gas compressed by flame propagation in an engine cylinder. The uncertainty of this method is within ± 10 K. The resolution of the temperature measurement was approximately 0.5 K, and was dependent upon both the sampling clock speed of the A/D converter and the length of the test section. This optical heterodyne interferometry system may also be used for other applications that require a fast response time to measure the density and pressure of a gas, and thereby obtain a transient temperature record.

DOI： 10.1299/kikaib.69.229

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Language：English   Publisher：Institute of Physics Publishing  

An infrared absorption method with a 3.392 umm He-Ne laser was used to determine the hydrocarbon fuel concentration near the spark plug in a spark-ignition engine. Iso-octane was used for the fuel. The pressure and temperature dependence of the molar absorption coefficient was clarified. The molar absorption coefficients of a multi-component fuel such as gasoline were estimated by using the coefficient of each component and considering the mass balance. A sensor was developed and installed in a spark plug, which was substituted in place of an ordinary spark plug in a spark-ignition engine. Light can pass from the sensor through the engine cylinder to measure the fuel concentration. The effects of liquid droplets inside the engine cylinder, mechanical vibrations and other gases such as H2O and CO2 on the measurement accuracy were considered. Four main conclusions were drawn from this study. First, the pressure and temperature effects on the molar absorption coefficient of liquid fuel vapour were determined independently in advance using a constant-volume vessel. The pressure and temperature dependence of the molar absorption coefficient was determined under engine firing conditions. Second, the molar absorption coefficients of a multi-component hydrocarbon fuel such as gasoline were estimated by considering the molar fraction of each component. Third, in situ measurements of the hydrocarbon fuel concentration in an actual engine were obtained using the spark plug sensor and the molar absorption coefficient of iso-octane. The concentration near the spark plug just before ignition was almost in agreement with the mean value that was obtained from the measurement of the flow rate made with a burette, which represented the mean value averaged over many cycles. And fourth, no liquid droplets were observed at near-idling conditions. The effects of other gases, such as CO, CO2 and H2O, can be neglected.

DOI： 10.1088/0957-0233/14/8/322

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It is necessary to increase thermal efficiency and reduce exhaust emission for internal combustion engines. Alternative fuels that are not made of petroleum are also one of the important factors. Hydrogen is expected to be one of the most prominent fuels in the near future for solving greenhouse problem, protecting environment and saving petroleum. In this study, a dual fuel engine operated with hydrogen and light oil was investigated. The configuration of the diesel engine was not changed except changing the injection timing over very wide range by setting an injection pump synchronized with the engine revolution. Hydrogen was supplied in an intake port with air and light oil was injected into the cylinder. The rate of heat release was determined from the pressure in the cylinder. Here, the concept of HCCI combustion was applied to this engine. When the injection timing of the light oil into the cylinder was advanced to 40 or 50 degrees before the compression top dead center, the light oil was well mixed with hydrogen-air mixture and the combustion became mild. As shown in Fig. A, NOx emissions decreased because of lean premixed combustion without the region of high temperature of burned gas. When hydrogen was mixed with inlet air, emissions of HC, CO and CO_2 decreased Without exhausting smoke while indicated thermal efficiency was slightly smaller than that in ordinary diesel combustion. In particular, both smoke and NOx were almost zero and HC was low when the injection timing is significantly advanced. Moreover, the effects of hydrogen ratio and spray angle on exhaust emissions and engine performance were investigated. If the operating conditions in early injection are chosen appropriately, it is considered that low NOx, HC, CO and CO_2,and zero smoke, can be achieved.[figure]

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Although homogeneous charge compression ignition (HCCI) engines are expected to have both higher thermal efficiency and lower nitrogen oxide (NOx) emissions, they still have problems with high hydrocarbon (HC) and carbon monoxide (CO) production, high rates of heat release, and difficulty in controlling auto-ignition. In order to control auto-ignition in HCCI engines, the reaction mechanism of auto-ignition must be understood. Dimethyl ether (DME), a promising alternative fuel that is suitable for compression ignition engines, shows very strong low-temperature kinetic reactions in HCCI. HCCI combustion shows a peculiar two-stage heat release. The first stage of the heat release curve is associated with low-temperature kinetic reactions, and the time delay between the first and main heat release is attributed to the negative temperature coefficient regime. A study of HCCI fueled with DME may provide useful information on the low-temperature kinetic reactions in HCCI operation. This study investigated the auto-ignition characteristics of an HCCI engine fueled with DME using a single[figure] cylinder engine with a transparent piston. The engine was operated at 800 rpm with a wide-open throttle. The intake-premixed mixture was preheated with an electric heater to promote auto-ignition. HCCI combustion was examined using instantaneous flame images obtained from a high-speed video. The influences of equivalence ratio and intake temperature on the characteristics of auto-ignition in the HCCI engine were investigated. Spectrum analyses of chemiluminescence using spectroscopy were carried out to investigate the two-stage heat release. Three main conclusions were drawn from this study. (1) The hot-flame reaction progresses homogeneously. DME combustion was found to be non-luminous. (2) With increasing intake temperature and equivalence ratio, varying heat release was observed. Three-stage heat release was also observed. (3) During the main heat release, the CO-O recombination spectrum was strong. There was a strong correlation between rate of heat release and the CO-O recombination spectrum.[figure]

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It is very important to know the hydrocarbon fuel concentration near the spark plug. The possibility of the concentration measurement near the spark plug using in-situ IR absorption method was presented. The fuel concentration near the spark plug was measured using an optical sensor with sapphire rods. A new optical sensor with double-pass measurement length was developed to increase the measurement accuracy. The light source with wavelength of 3.392 μm was introduced into an optical fiber and guided to a spark plug. This optical sensor was constructed by modifying a commercially available instrumented spark plug. Original is an abstract.

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The flame propagation and the combustion characteristics of stratified fuel concentration field were studied using a cylindrical constant volume vessel. A swirling fuel-air mixture was produced in the vessel. A rich fuel concentration was formed near the center of the vessel by the injection of propane and lean mixture near the wall. The gas flow field was obtained with a laser Doppler velocimeter in advance. The pressure history in the combustion chamber was analyzed to determine the combustion characteristics. The flame could propagate and the combustion occurred even in an ultra lean mixture of equivalence ratio of 0.3:1 in total. As the fuel concentration near the spark location approximates stoichiometric mixture ratio, flame propagation of the initial stage of the combustion became faster. When stratified mixtures with the same pattern of fuel concentration but different turbulence intensities were considered, the main combustion period decreased with turbulence intensity, since the burning velocity also increased. Original is an abstract.

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Various global environmental issues are related to the use of internal combustion engines, including air pollution and energy concerns. With homogeneous charge compression ignition (HCCI) engine, it is possible to operate with ultra lean premixed mixtures and to lead low NOx and soot-particle emissions. The temperature of the unburned mixture in a HCCI engine, fueled with dimethyl ether, was measured using fiber-optic heterodyne interferometry along a line of sight. The measurement accuracy of the developed system was sufficient to determine the temperature history of unburned mixture in HCCI operation. The uncertainty of this method was within ± 15K. The resolution of temperature measurements was ∼ 0.5 K, and depended on the sampling clock speed of the A/D converter and the length of the test section. Original is an abstract.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

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Language：English   Publisher：IOP PUBLISHING LTD  

A fibre-optic heterodyne interferometry system was developed to obtain the temperature histories of an unburned mixture with high temporal resolution non-intrusively. In laser interferometry, the effective optical path length of the test beam changes with the gas density and corresponding changes of the refractive index. Therefore, the temperature history of an unburned gas can be determined from the pressure and phase shift of the heterodyne signal. A polarization-preserving fibre is used to deliver the test beam to and from the test section, to improve the feasibility of the system as a sensor probe. The temperature of the unburned mixture in the end-gas region of a constant-volume combustion chamber and in an engine cylinder was measured during flame propagation. The accuracy of the measurements and the feasibility of this system are discussed. The measurement accuracy of our system was sufficient to be applied to temperature history measurement of an unburned gas compressed by flame propagation in a constant-volume combustion chamber. The uncertainty of this method is within +/-10 K. The resolution of the temperature measurement is approximately 0.5 K, and is dependent on both the sampling clock speed of the A/D converter and the length of the test section, This fibre-optic heterodyne interferometry system can also be used for other applications that require a transient temperature with a fast response time.

DOI： 10.1088/0957-0233/13/1/316

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Language：English   Publisher：Elsevier Ltd  

Recently, improving the thermal efficiency and reducing the exhaust emissions of internal combustion engines have become crucial. To this end, it is important to determine the fuel concentration in the vicinity of the spark plug near the spark timing, because initial combustion affects the subsequent main combustion in spark-ignition engines. In this study, a fiber optic system linked to an optical sensor installed in the spark plug, by means of which light can pass through the combustion chamber, was developed to determine the fuel concentration near the spark plug using an IR absorption method. A He-Ne laser with a wavelength of 3.39 μm that coincides with the absorption line of hydrocarbons was used as a light source. By exchanging an ordinary spark plug for this spark plug with the optical sensor, successive measurement of fuel concentration before the spark timing near the spark plug was performed in a port-injection spark-ignition engine fueled with iso-octane under the firing condition. The effects of pressure and temperature on the molar absorption coefficient of fuel were clarified in advance. The air/fuel ratio averaged for many cycles near the spark plug with this optical system agreed with that measured with a buret, which represented the mean value averaged over a protracted period. Next, this sensor was applied to determine the air/fuel ratio quantitatively in a direct-injection gasoline engine. As a result, it was clarified that the air/fuel ratio and its standard deviation near the spark plug have a strong relationship to stable engine operation.

DOI： 10.1016/S1540-7489(02)80094-3

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A dual fuel engine fueled with methane from an inlet port and ignited with diesel fuel was prepared. This study focuses on the effects of early injection and exhaust gas recirculation (EGR) on the characteristics of combustion and exhaust emissions. The injection timing was changed between TDC and 50 degrees before the TDC. In the early injection timing, smoke was never seen and hydrocarbons were smaller compared with those at the normal injection timing. However, the combustion becomes too early to obtain an appropriate torque when the equivalence ratio increases. Then, moderate EGR was very effective to force the combustion to retard with lower NOx, higher thermal efficiency and almost the same hydrocarbons and carbon monoxide. The engine operated even under the condition of stoichiometric mixture. Copyright © 2002 SAE International.

DOI： 10.4271/2002-01-2723

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A dual fuel engine fueled with methane from an inlet port and ignited with diesel fuel was prepared. This study focuses on the effects of early injection and exhaust gas recirculation (EGR) on the characteristics of combustion and exhaust emissions. The injection timing was changed between TDC and 50 degrees before the TDC. In the early injection timing, smoke was never seen and hydrocarbons were smaller compared with those at the normal injection timing. However, the combustion becomes too early to obtain an appropriate torque when the equivalence ratio increases. Then, moderate EGR was very effective to force the combustion to retard with lower NOx, higher thermal efficiency and almost the same hydrocarbons and carbon monoxide. The engine operated even under the condition of stoichiometric mixture. Copyright © 2002 SAE International.

DOI： 10.4271/2002-01-2723

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Language：English   Publisher：Elsevier Ltd  

Recently, improving the thermal efficiency and reducing the exhaust emissions of internal combustion engines have become crucial. To this end, it is important to determine the fuel concentration in the vicinity of the spark plug near the spark timing, because initial combustion affects the subsequent main combustion in spark-ignition engines. In this study, a fiber optic system linked to an optical sensor installed in the spark plug, by means of which light can pass through the combustion chamber, was developed to determine the fuel concentration near the spark plug using an IR absorption method. A He-Ne laser with a wavelength of 3.39 μm that coincides with the absorption line of hydrocarbons was used as a light source. By exchanging an ordinary spark plug for this spark plug with the optical sensor, successive measurement of fuel concentration before the spark timing near the spark plug was performed in a port-injection spark-ignition engine fueled with iso-octane under the firing condition. The effects of pressure and temperature on the molar absorption coefficient of fuel were clarified in advance. The air/fuel ratio averaged for many cycles near the spark plug with this optical system agreed with that measured with a buret, which represented the mean value averaged over a protracted period. Next, this sensor was applied to determine the air/fuel ratio quantitatively in a direct-injection gasoline engine. As a result, it was clarified that the air/fuel ratio and its standard deviation near the spark plug have a strong relationship to stable engine operation.

DOI： 10.1016/S1540-7489(02)80094-3

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Language：English   Publisher：SPRINGER-VERLAG BERLIN  

Optical heterodyne interferometry was validated to measure the transient temperature of a gas by comparing the temperature history of unburned gas in a combustion chamber, caused by compression due to flame propagation, obtained by the heterodyne interferometry with temperature obtained by assuming adiabatic change. When the density of gas changes, the effective optical path length of the test beam changes with corresponding changes of the refractive index. Therefore, the temperature history of the gas can be determined by measuring the pressure and the phase shift of the interference signal. As a result, it is clearly recognized that a non-intrusive measurement in the transient gas temperature was made successfully by the optical heterodyne interferometry. The resolution of the temperature measurement is approximately 0.5 K, and is dependent upon both the sampling clock speed of the A/D converter and the length of the test section. Moreover, a polarization-preserving fiber was used to deliver the test beam to and from the test section to improve the feasibility of the system as a sensor probe. It may also be applied to other system requiring fast response density and temperature measurement of a gas, the latter necessitating a simultaneous record of transient pressure.

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Language：English   Publisher：Elsevier Ltd  

Recently, improving the thermal efficiency and reducing the exhaust emissions of internal combustion engines have become crucial. To this end, it is important to determine the fuel concentration in the vicinity of the spark plug near the spark timing, because initial combustion affects the subsequent main combustion in spark-ignition engines. In this study, a fiber optic system linked to an optical sensor installed in the spark plug, by means of which light can pass through the combustion chamber, was developed to determine the fuel concentration near the spark plug using an IR absorption method. A He-Ne laser with a wavelength of 3.39 μm that coincides with the absorption line of hydrocarbons was used as a light source. By exchanging an ordinary spark plug for this spark plug with the optical sensor, successive measurement of fuel concentration before the spark timing near the spark plug was performed in a port-injection spark-ignition engine fueled with iso-octane under the firing condition. The effects of pressure and temperature on the molar absorption coefficient of fuel were clarified in advance. The air/fuel ratio averaged for many cycles near the spark plug with this optical system agreed with that measured with a buret, which represented the mean value averaged over a protracted period. Next, this sensor was applied to determine the air/fuel ratio quantitatively in a direct-injection gasoline engine. As a result, it was clarified that the air/fuel ratio and its standard deviation near the spark plug have a strong relationship to stable engine operation.

DOI： 10.1016/S1540-7489(02)80094-3

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

Direct injection spark ignition (DISI) engines, which are able to achieve better thermal efficiency and higher output power simultaneously, have been developed. The DISI engine is operated unthrottled in an ultra-lean condition by distinctively stratifying the charge and by preparing a fuel-rich mixture around the spark plug. However, the effects of mixture inhomogeneity and simultaneous details of the flow field at the time of the spark on the combustion have not yet been clarified. In this research, the fundamental flame propagation and combustion characteristics of a stratified fuel-air mixture, similar to mixtures used in direct injection spark ignition (DISI) engines, were investigated. A swirling fuel-air mixture was produced in a disc-type combustion chamber by accelerating the mixture tangentially. Propane was injected into the center of the combustion chamber at an injection pressure of 0.3 MPa. The strong swirl combined with the gas injection created an axisymmetric fuel-rich mixture near the spark location and a lean mixture near the wall. The swirl, gas injection and spark timing changed the flow field, turbulence intensity, and inhomogeneity of the fuel-air mixture. The mixture was ignited at the center of the vessel. The fuel concentration distribution and the swirling flow field at the time of the spark were measured using LIF and LDV, respectively. Experimental tests were performed for various fuel distributions and different swirl flow at the ignition timing. Flame propagation and the combustion characteristics of an inhomogeneous fuel-air mixture are discussed using instantaneous flame images obtained from a high-speed video and the pressure history. Three main conclusions are drawn from this work. First, strongly swirling flow with gas injection at the center generates successive inhomogeneous fuel concentrations. By changing the period between gas injection and ignition, various gradients of inhomogeneous mixture concentrations and equivalence ratios can be obtained in the vicinity of the spark location. A stratified charge with an appropriate mixture near the spark location allows the flame to propagate and combustion to occur, even when an ultra-lean fuel-air mixture is used. Second, the stratified stoichiometric mixture in the vicinity of the spark location propagates more rapidly than in the homogeneous case with the same overall equivalence ratio, resulting in a higher rate of pressure increase and a shorter ignition delay time. Third, when stratified mixtures with the same pattern of fuel concentration but different turbulence intensities are considered, the main combustion period decreases with turbulence intensity at an overall equivalence ratio of 0.30, since the burning velocity also increases.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

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A fiber optical heterodyne interferometry system was developed to obtain high temporal resolution temperature histories of unburned and burned gases non-intrusively. The effective optical path length of the test beam changes with the gas density and corresponding changes of the refractive index. Therefore, the temperature history of the gas can be determined from the pressure and phase shift of the interference signal. The resolution of the temperature measurement is approximately 0.5 K, and is dependent upon both the sampling clock speed of the A/D converter and the length of the test section. A polarization-preserving fiber is used to deliver the test beam to and from the test section, to improve the feasibility of the system as a sensor probe. This optical heterodyne interferometry system may also be used for other applications that require gas density and pressure measurements with a fast response time, or a transient temperature record. Copyright © 2001 Society of Automotive Engineers, Inc.

DOI： 10.4271/2001-01-1922

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Language：Japanese   Publisher：Japan Society of Mechanical Engineers  

A concept of "compound-cluster combustion" is proposed in order to investigate an applicability of group combustion theory to practical spray combustion, in which strong turbulent coherent vortex is formed and influenced spray behavior significantly. This turbulent coherent structure causes inhomogeneous droplet distribution and its population, and causes interphase exchange of properties and combustion under the effects of preferential interactions. In application of group combustion theory to practical spray combustion, these points were taken into account and phase Doppler measurement (PDA) data was analyzed : there are multiple clusters, characterized by their size and followabiliy (Stokes effect)
clusters of different droplet sizes are produced at the same time in the flow field
the turbulent scale on cluster formation should be considered by the droplet's inter-arrival time statistics. In this research, PDA measurement with high sampling-rates and high validation- rates was carried out by optimizing the PDA set-up parameters. The integral length scale of each size cluster and the inter-arrival time statistics of the droplets can be obtained, based on the instantaneous droplet velocities as well as, but also Stokes' number, cluster size and inter-arrival time. The size-classified group combustion number is evaluated by the experimental data to demonstrate the applicability of group combustion theory. The interaction between the turbulent coherent vortex and small droplets of less than 30 μm generates essential clusters of the droplets and its combustion can be characterized by group combustion. The size of these clusters corresponds to the integral scale of the turbulent vortices. The effect of turbulent coherent structure on compound- cluster formation is examined and this effect is successfully evaluated by the Stokes effect.

DOI： 10.1299/kikaib.67.841

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Language：Japanese   Publisher：日本工業出版  

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Hydrogen is expected to be one of the most prominent fuels in the near future for solving greenhouse problem, protecting environment and saving petroleum. In this study, a dual fuel engine of hydrogen and diesel oil was investigated. Hydrogen was inducted in a intake port with air and diesel oil was injected into the cylinder. The injection timing was changed over extremely wide range. When the injection timing of diesel fuel into the cylinder is advanced, the diesel oil is well mixed with hydrogen-air mixture and the initial combustion becomes mild. NOx emissions decrease because of lean premixed combustion without the region of high temperature of burned gas. When hydrogen is mixed with inlet air, emissions of HC, CO and CO2 decrease without exhausting smoke while brake thermal efficiency is slightly smaller than that in ordinary diesel combustion. In particular, both smoke and NOx are almost zero and HC is low when the injection timing is significantly advanced although the engine operation becomes unstable. Copyright © 2001 Society of Automotive Engineers, Inc.

DOI： 10.4271/2001-01-3503

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Language：English   Publisher：AMER INST PHYSICS  

The effect of the acoustic streaming on the mass transfer from the surface of a sphere positioned in an ultrasonic acoustic levitator is studied both experimentally and theoretically. Acoustic levitation using standing ultrasonic waves is an experimental tool for studying the heat and mass transfer from small solid or liquid samples, because it allows an almost steady positioning of a sample at a fixed location in space. However, the levitator introduces some difficulties. One of the main problems with acoustic levitation is that an acoustic streaming is induced near the sample surface, which affects the heat and mass transfer rates, as characterized by increased Nusselt and Sherwood numbers. The transfer rates are not uniform along the sample surface, and the aim of the present study is to quantify the spatial Sherwood number distribution over the surface of a sphere. The experiments are based on the measurement of the surface shape of a sphere layered with a solid substance as a function of time using a charge-coupled device (CCD) camera with backlighting. The sphere used in this research is a glass sphere layered with a volatile solid substance (naphthalene or camphor). The local mass transfer from the surface both with and without an ultrasonic acoustic field is investigated in order to evaluate the effect of the acoustic streaming. The experimental results are compared with predictions following from the theory outlined [A. L. Yarin, M. Pfaffenlehner, and C. Tropea, J. Fluid Mech. 356, 65 (1998); A. L. Yarin, G. Brenn, O. Kastner, D. Rensink, and C. Tropea, ibid. 399, 151 (1999)] which describes the acoustic field and the resulting acoustic streaming, and the mass transfer at the surface of particles and droplets located in an acoustic levitator. The results are also compared with the experimental data and with the theoretical predictions of Burdukov and Nakoryakov [J. Appl. Mech. Tech. Phys. 6, 51 (1965)], which are valid only in the case of spherical particles much smaller than the sound wavelength. Good agreement between experiment and the theory of Yarin is demonstrated. The time-averaged heat and mass transfer rates over a sphere surface are greatest at the sphere's equator and least at its poles in the experiment as predicted by the theory (the ultrasonic standing wave spans the vertical axis passing through the poles). The measured distribution of the mass transfer rate over the sphere surface also agrees with the theoretical predictions, which shows that in strong acoustic fields sublimation (or evaporation) results from the acoustic streaming. (C) 2000 American Institute of Physics. [S1070-6631(00)02104-8].

DOI： 10.1063/1.870347

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In diesel engines, there is a problem that both smoke and nitrogen oxide cannot be reduced simultaneously. There have been many studies on solving this problem. One of the solutions is the utilization of gaseous fuel. Gaseous fuel is inducted from an intake port and the combustion starts by injecting light oil. Hydrogen is considered as a future fuel without exhausting carbon dioxide. In this study, hydrogen was inducted from the intake port into the cylinder of a diesel engine and light oil was injected in the cylinder. The heat release rate was determined from the pressure history in the cylinder. The relation between the heat release rate and the exhaust emissions are discussed. As a result, when hydrogen is mixed with the inlet air, exhaust emissions such as smoke, hydrocarbon, CO, CO_2, and NOx are reduced simultaneously while brake thermal efficiency is slightly lower.

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The fundamental flame propagation and combustion characteristics of a stratified fuel-air mixture are investigated. Swirling turbulent flow with a rich fuel-air concentration is generated in a constant volume cylindrical vessel. The fuel concentration distribution and swirling flow field at the timing of the spark are measured using LIF and LDV, respectively. The mixture is ignited at the center of the vessel. Two main conclusions are drawn from this work. First, the strongly swirling flow with gas injection at the center generates successive inhomogeneous fuel concentrations. Various gradient and equivalence ratios in the vicinity of the spark location are obtained by changing the period between gas injection and ignition. Under a stratified charge condition, with an appropriate mixture near the spark location, the flame can propagate and combustion occurs, even with an ultra lean fuel-air mixture. Second, the stratified mixture with a stoichiometric mixture in the vicinity of the spark location propagates more rapidly than the homogeneous case with the same overall equivalence ratio. Both a higher rate of pressure rise and a shorter ignition delay time were achieved.

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Publisher：American Institute of Aeronautics and Astronautics  

© l999 American Institute of Aeronautics & Astronautics. In order to understand the combustion characteristics of droplet clusters consisting of a number of cluster sizes of i.nhomogeneous droplets, measurements of local chemiluminescence (OH, CH arid C,) were taken simultaneously with measurements of the droplets’ size and velocity in a spray flame stabilized by a recirculating flow. The limitations of using Cassegmin optics to measure chemiluminescence in actual spray flames was investigated. The Cassegrain optics developed were able to detect the local chemiluminescences of OK CH and C, in an actual spray flame. The intensity ratio of the time-averaged local chemiluminescences (&/OH) showed the local equivalence ratio of the fuel droplets in the spray flame. These five signals were analyzed statistically and spectrally, and finally combined to produce cross-correlation coefficients. These data can provide inhormation about the combustion characteristics of droplet clusters. The change in the burning mode of droplet clusters, from external group combustion to internal group combustion, was confirmed experimentally.

DOI： 10.2514/6.1999-210

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In order to clarify the effects of different kinds of fuel and fuel equivalence ratio on flame structure, a numerical simulation of triple flame developed in a co-flowing methane-air or hydrogen-air mixture and air stream was made taking into account the elementary chemical reaction mechanism. The following conclusions were reached: (1)The relation between the apparent burning velocity of the triple flame and the fuel equivalence ratio shows a similar tendency to that of the one-dimensional premixed flame of the corresponding fuel. However, the fuel equivalence ratio at which the apparent burning velocity is the largest is a little larger than that of the one-dimensional premixed flame. The apparent burning velocities are two and three times higher than that of the one-dimensional premixed flame for the methane-air or hydrogen-air mixture. ( 2 )The flame thrusts out forward in the downstream of the boundary between mixture and air stream, and a part of the flow is bent and forks out in this protruding flame so that a triple flame is originated ; this triple flame is composed of fuel rich and lean premixed flame branches and a diffusion flame branch. The change in shape of the convex part, caused by the effect of the one-dimensional premixed flame, is further promoted by the effect of hydrodynamic instability originated in the expansion brought about by heat release. A considerably strong diffusion flame branch exists almost in the center of the two premixed flame branches for the methane-air mixture, while a considerably weak diffusion flame branch approaches the fuel lean premixed flame branch for the hydrogen-air mixture. ( 3 )Near the fuel equivalence ratio at which the burning velocity of the one-dimensional premixed flame is the largest, the effect of the one-dimensional premixed flame becomes large and the fuel rich premixed flame advances and becomes vertical to the flow direction. As a result, the effect of hydrodynamic instability is weakened. Thus, both of these effects demonstrate that the fuel equivalence ratio at which the apparent burning velocity is the largest is a little larger than that of the one-dimensional premixed flame.

DOI： 10.1299/kikaib.65.775

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The purpose of the present research is to investigate the aerodynamic characteristics of evaporating droplet near the burner where flame is hold by the recirculating flow and to characterize droplet aerodynamic response regarding follow or penetration and turbulent interaction with the surrounding air by classifing droplets. Aerodynamic characteristics of combusting spray were measured in a small industrial oil furnace by a phase Doppler anemometer. The size-classified technique was used together with the relative Reynolds number and the recombined two-dimensional size-classified droplet velocity. The results show that the two-dimensional behavior of a spray flame can be represented. The size-classified droplet technique can provide very useful information on droplet aerodynamics and dispersion. The follow/penetration characteristics of spray can be understood very well in consideration of the features of classified droplet in combustion condition. Larger droplets had a large mass and inertia, and thus could penetrate through the recirculation flow region. Consequently larger droplets form large luminous flame. On the other hand, smaller droplets were entrained by the turbulent air flow and played a role of flame-holder. In addition, the interaction between fuel droplets and air flow is a process that significantly affects flame-holding mechanism of spray flames.

DOI： 10.1299/kikaib.65.790

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Publisher：IOP Publishing  

A high-luminosity-light-collection system for highly spatial detection of chemiluminescence of radical species in flames has been developed. The system, multi-colour integrated Cassegrain receiving optics (MICRO) is based upon a Cassegrain-type configuration, which implies that it employs only reflective components (in combination with an optical fibre for light collection). It provides therefore spherical-and chromatic-aberration-free detection, which is of importance for high-spatial-resolution measurements and for the simultaneous monitoring of signals in different wavelength regions from a given spatial volume. The effective light-collection volume has been estimated to be only 1.6 mm × 0.2 mm × 0.2 mm by ray-tracing techniques, which is more than three orders of magnitude smaller than that provided by a corresponding simple single-lens system and comparable to that of laser-based techniques, e.g. Doppler anemometry. The system is also easily aligned since the active probe volume can be visualized by sending in visible light through the system in the reverse direction. In order to demonstrate the performance of the system, OH-radical chemiluminescence in a Bunsen flame was monitored using MICRO and compared with the ion-current signal from a Langmuir probe with a minute sensor tip. A good correlation between the fluctuations in the two signals could be obtained, proving the high spatial and temporal resolution of the MICRO system.

DOI： 10.1088/0957-0233/10/12/316

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Publisher：Japan Society of Mechanical Engineers  

Spot monitoring of radical chemiluminescence is especially useful for flame diagnostics, if the measuring control volume size can be clearly defined. However, a typical light collection system consisting of a spherical lens and a pinhole suffers from its wide and long control volume, as well as its significant chromatic aberration between UV and visible ranges in simultaneous multi-color measurement. In some cases, researchers were obliged to insert a control-volume limiting device into the flame for observing the local emission intensities of radical chemiluminescence. To resolve these problems, we have developed a light collection probe of Cassegrain type, which consists of a set of concave and convex mirrors combined with an optical fiber cable, and is free from both chromatic and spherical aberrations, which was named Multi-color Integrated Cassegrain Receiving Optics (MICRO). The spatial resolution was analyzed by the ray-tracing method, and the effective control volume size was estimated as 1.6 mm-long and 200 μn diameter, which is as small as that of LDA or PDA.

DOI： 10.1299/kikaib.64.925

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© 1997, American Institute of Aeronautics and Astronautics, Inc. Investigation of the relationship between droplet dispersion and turbulent mixing in a pressure-atomized spray flame with a recirculation region was done. Time-resolved information of instantaneous droplet velocities and interarrival-time statistics of the droplet were obtained and examined in order to observe the turbulent mixing and follow/ penetration criteria. In order to observe the detailed structure of spray flames, the size and velocity of droplets instantaneously were measured by phase Doppler anemometer. The group combustion number was calculated by the experimental data in order to elucidate the actual aspects of group combustion. It was found that the turbulent coherent structures were contributed in order to form droplet clusters of small droplets under 30 µm because of its momentum, inertia and followability. The cluster dimensions obtained corresponded with the integral scale of turbulent vortex measured. While, large droplets penetrates strongly due to large momentum and less shear flow information along the spray cone so that group combustion characteristics could not be observed. The interaction and its relation of turbulent scale and group combustion cluster was discussed with measured data for a practical oil burner of 0.1MW.

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Language：English   Publisher：Begell House Inc.  

The purpose of this study is to investigate fuel droplet dispersion and mixture formation in a practical twin-fluid atomizer for a practical oil furnace of 1 MW. In this experiment, droplet size, velocity and dispersion data were measured to show two-dimensional droplet velocity vectors using phase Doppler technique (PDA/PDPA). Fuel droplet dynamics and spray characteristics are discussed by two-dimensional size-classified droplet vector and their slip velocities vector. The spray dynamics is investigated by not only Sauter mean diameter but also each size-classified velocity. The results showed that the size classified technique was suitable and the strong penetration of small droplet near nozzle and the much entrainment flow were yielded at the middle of the jet plane. The injection pressure was varied to show the spray characteristics changes for different conditions.

DOI： 10.1615/InterJFluidMechRes.v24.i1-3.140

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Publisher：Japan Society of Mechanical Engineers  

Three dimensional measurements of velocity and gas flux measurements of O2, CO2 flux near burner of oil furnace were demonstrated to show a flame holding mechanism and fluctuation characteristics. The use of convective flux in flame was not accurate but found to be applicable in whole combustion region in a furnace. Two pairs of recirculating flow region rotated in swirl direction due to the slit flow and its timescale was about 5-10 msec. The timescale of turbulence and CO, CO2 gas variation were compared in order to show the flame holding mechanism in a transparent evaporating region. The comparison results show that the timescale of turbulence and chemical species fluctuation were the same order.

DOI： 10.1299/kikaib.62.1599

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