研究者詳細 - 河原　伸幸

MISC - 河原　伸幸

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Effect of acoustic streaming on the mass transfer from a sublimating sphere

N Kawahara, AL Yarin, G Brenn, O Kastner, F Durst

PHYSICS OF FLUIDS 12 ( 4 ) 912 - 923 2000年4月

記述言語：英語出版者・発行元：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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314 二元燃料予混合圧縮着火ディーゼル機関における排気特性(エンジンシステムII)

冨田栄二, 河原伸幸, 浜本嘉輔, 藤田将語, 朴振宇

講演論文集 5 ( 1 ) 107 - 108 2000年2月

310 小型センサを使用した3.39μm赤外吸収法による燃焼室内燃料濃度変化の計測(エンジンシステムI)

冨田栄二, 河原伸幸, 吉山定見, 雑賀俊喜, 浜本嘉輔

講演論文集 5 ( 1 ) 99 - 100 2000年2月

Fuel Concentration Measurement near Spark-Plug in a Spark-Ignition Engine by 3.39m Infrared Laser Absorption Method

Tomita, E, Kawahara, N, Yoshiyama, S, Hamamoto, Y

Proc. of 22nd Task Leaders Meeting, Int. Energy Agency Executive Committee on Energy Conservation and Emission Reduction in Combustion 2000年

Transient Temperature Measurement of Unburned Gas Using Optic Heterodyne Interferometry

Kawahara, N, Tomita, E, Kamakura, H

10th Int. Symp. on Application of Laser Techniques on Fluid Mechanics 2000年

A Study on Hydrogen Combustion Ignited with Light Oil in a Dual Fuel Engine

Tomita, E, Kawahara, N, Hamamoto, Y, Zhen-Yu Piao, Fujita, S

4th JSME-KSME Thermal Engineering Conference 3 "3 - 415"-"3-420" 2000年

記述言語：英語出版者・発行元：日本機械学会

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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Flame Propagation of Inhomogeneous Fuel-Air Mixture with Swirl in a Constant-Volume Vessel

Kawahara, N, Tomita, E, Yoshiyama, S, Nishiyama, A, Hamamoto, Y

4th JSME-KSME Thermal Engineering Conference 3 "3 - 109"-"3-114" 2000年

記述言語：英語出版者・発行元：日本機械学会

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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Measurements of the Combustion Characteristics of Compound Clusters in Pressure-Atomized Spray Flame

Kawahara, N, Ikeda, Y, Nakajima, T

37th AIAA Aerospace Sciences Meeting and Exhibit, AIAA Paper No.99-0210 1999年1月

© 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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Effects of different kinds of fuel and fuel equivalence ratio on flame structure of triple flame

Hiroshi Yamashita, Nobuyuki Kawahara, Nag Jung Choi

Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 65 775 - 782 1999年1月

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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Size-Classified Droplets Dynamics of Combusting Spray in Oil MW Oil Furnace

Nobuyuki Kawahara, Yuji Ikeda, Tsuyoshi Nakajima

Jaurnal of the Japan Society of Mechanical Engineering 65 ( 630 ) 790 - 797 1999年1月

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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Development of Light-Collecting Probe with High Spatial Resolution Applicable to Randomly Fluctuating Combustion Fields

Akamatsu, F, Wakabayashi, T, Tsushima, S, Katsuki, M, Mizutani, Y, Ikeda, Y, Kawahara, N, Nakajima, T

Measurement Science and Technology 10 ( 12 ) 1240 - 1246 1999年1月

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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Observation of Compound-Cluster Combustion in Pressure-Atomized Spray Flame

Kawahara, N, Ikeda, Y, Nakajima, T

Proc. of 2nd ASPACC 1999年

局所自発光計測による噴霧群燃焼構造の観察

河原伸幸, 池田裕二, 中島健

微粒化シンポジウム講演論文集 = Symposium (ILASS-Japan) on Atomization 8 69 - 74 1999年

位相ドップラ法による噴霧火炎中の燃料油滴の粒径と速度の計測

河原伸幸

高温学会誌 24 ( 3 ) 102 - 110 1998年5月

Development of a Multi-Color light collection probe with high spatial resolution (1st Report, Evaluation of spatial resolution by Ray-Tracing Method)

Takashi Wakabayashi, Fumiteru Akamatsu, Masashi Katsuki, Yukio Mizutani, Yuji Ikeda, Nobuyuki Kawahara, Tsuyoshi Nakajima

Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 64 ( 619 ) 925 - 930 1998年1月

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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Droplet dispersion and turbulent structure in a pressure-atomized spray flame

Nobuyuki Kawahara, Yuji Ikeda, Tsuyoshi Nakajima

35th Aerospace Sciences Meeting and Exhibit 1997年1月

© 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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Fuel droplet dynamics and dispersion of practical twin-fluid atomizer for oil furnace

Y. Ikeda, N. Tsuchimoto, N. Kawahara, T. Nakajima

International Journal of Fluid Mechanics Research 24 ( 1-3 ) 138 - 148 1997年

記述言語：英語出版者・発行元：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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Flame holding in a gun-type oil burner (fluctuation characteristics and concentration variation)

Yuji Ikeda, Nobuyuki Kawahara, Tsuyoshi Nakajima

Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 62 ( 596 ) 1599 - 1607 1996年1月

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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Combusting Flow Simulation in an oil Furnace

Yuji Ikeda, Nobuyuki Kawahara, Tsuyoshi Nakajima

Jaurnal of the Japan Society of Mechanical Engineering 62 ( 598 ) 2481 - 2489 1996年1月

Combusting flow simulations in an oil furnace (0.1 MW) were carried out in order to investigate droplet behavior and the flame-holding mechanism. Measurements made by a phase Doppler anemometer were also examined to elucidate the followability characteristics in recirculation flow. The results show that a droplet under 30 microns can follow the flow but a droplet over 50 microns penetrates. The use of connective flux of O2and CO2both in the flame and the entire furnace was examined and the results demonstrated that it was very useful to show the self-recirculating flow in furnaces.

DOI： 10.1299/kikaib.62.2481

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Flux Measurements of O₂, CO₂ and No in Oil Furnace

Yuji Ikeda, Nobuyuki Kawahara, Tsuyoshi Nakajima

Journal of the Japan Society of Mechanical Engineering 61 ( 581 ) 332 - 338 1995年1月

記述言語：日本語出版者・発行元：The Japan Society of Mechanical Engineers

The flow velocity measurements and flux measurements of gas species of O2, CO2and NO in an oil furnace were carried out. The velocity profiles in combustion and noncombustion were measured by the developed LDV, and the results show that the reversing flow regions for both cases were located at the same place and their volumes were almost equal. The comparisons of measured concentration and flux obtained using velocity and temperature were performed in spray combustion. The results show that there is little difference in the flame region but a large discrepancy outside of the flame region. The generated gas species in the flame and its convection outside of the flame were discretized, and the application of flux in spray combustion research was found to be very useful and effective. © 1995, The Japan Society of Mechanical Engineers. All rights reserved.

DOI： 10.1299/kikaib.61.332

<河原 伸幸>

MISC - 河原 伸幸

<河原　伸幸>

MISC - 河原　伸幸