論文 - 横森　剛

Numerical study on propagation and NO reduction behavior of laminar stratified ammonia/air flames

Tomidokoro T., Yokomori T., Im H.G.

Combustion and Flame （Combustion and Flame）  241 2022年07月

ISSN  00102180

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In recently developed ammonia combustion technologies such as swirl flow and staged combustion, locally rich or lean pockets of unburned mixtures may occur due to insufficient mixing. This results in a premixed flamelet propagating into a gradually leaner or richer mixture. The present study aims to numerically investigate the propagation of laminar ammonia/air premixed flames in compositionally stratified mixtures. Results indicate that the flame speed in a rich-to-lean stratified mixture is increased from that in corresponding homogeneous mixtures at each local equivalence ratio. In contrast, the stratified flame speed is decreased in a lean-to-rich stratified mixture. The response of the stratified flame speed is attributed to variation in the amount of H2 in the burned gas. In the rich-to-lean stratified flame, an extra amount of H2 diffuses into the reaction zone to enhance chain-branching reactions which produce H radicals. The increased H radicals then promote dehydration reactions, resulting in an increased fuel consumption rate. In the lean-to-rich stratified flame, the opposite process takes place. The above mechanism is similar to the so-called back-support effect observed in methane/air stratified flames. Meanwhile, in both rich-to-lean and lean-to-rich stratified flames, additional NO reduction occurs in the stoichiometric region of the burned gas. This is facilitated by unburned ammonia diffusing from the neighboring rich burned gas mixing with O/H radicals diffusing from the neighboring lean burned gas, resulting in a production of extra NHi radicals which readily reduce NO. Therefore, NO emission in stratified flames is expected to be lower than that estimated from the emission characteristics in homogeneous mixtures. Although similar to the well-known thermal DeNOx mechanism, the current NO reduction process occurs under a much higher temperature due to the abundance of radical species. A similar phenomenon is expected to be observed in a triple flame configuration, which requires future investigations.

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Experimental Investigation of the Effects of Fuel Injection on the Cycle-to-Cycle Variation of the In-Cylinder Flow in a Direct-Injection Engine Using High-Speed Particle Image Velocimetry Measurement

Kaneko Y., Nagashima T., Tomidokoro T., Matsuda M., Yokomori T.

SAE International Journal of Engines （SAE International Journal of Engines）  15 （ 6 ）  2022年02月

ISSN  19463936

　概要を見る

In a direct-injection (DI) engine, the in-cylinder flow is complex. Fluctuations of DI and in-cylinder flow, and the relationships between those fluctuations, are considered to affect the cycle-to-cycle variation (CCV) of combustion. However, neither the relationship between the injection conditions and the CCV of the in-cylinder flow nor the effect of the in-cylinder tumble flow on the spray has been clarified in detail. In this study, a single-cylinder optical engine was used to perform high spatial resolution particle image velocimetry (PIV) measurements and to photograph spray behavior throughout the cylinder. The spray timing was changed to investigate the timing's effects on the in-cylinder flow, the CCV, and tumble vortex center behavior. The penetration length was calculated from the spray images and compared with the PIV measurement results. The PIV results showed that the behavior of the bulk flow in the cylinder, the position of the center of the tumble vortex, and the CCV of the velocity changed depending on the presence or absence of DI and the injection timing. The overall trend was that the shorter the time elapsed after injection, the stronger the effect on the in-cylinder flow remained. The results of spray imaging revealed that the ambient flow velocity affected the direct spray at the time of injection when the flow velocity was high in the spray direction and that the spray extended faster. In addition to the advantage of the longer diffusion time, the fast in-cylinder flow in the same direction as the direct jet did not cause much momentum exchange with the spray, while making it easier for the spray to diffuse throughout.

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火炎を用いたコアシェル粒子合成技術

横森 剛, 富所 拓哉

日本燃焼学会誌 （一般社団法人 日本燃焼学会）  63 （ 205 ） 201 - 209 2021年

ISSN  1347-1864

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<p>Core shell particles comprise a core content and a coating shell of another material. The core shell structure can realize a new functional material that cannot be realized by a particle which has only a single composition. Wet chemical synthesis is commonly used in the fabrication of core–shell particles, but recently, some reports on flame aerosol synthesis of core-shell particles have been published. Flame aerosol synthesis can offer continuous one-step production process including high-temperature treatment, and results in high-purity fine crystalline particles. Therefore, it is expected that flame aerosol synthesis method for core-shell particles will be further developed in the future. In this paper, we explain the details of flame aerosol synthesis method for core-shell particles and give an interpretation of the physical processes.</p>

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共添加燐光体における異波長ライフタイム特性とその２波長ライフタイム同時測定による温度測定性能向上

松下 佑樹, 横森 剛

日本機械学会関東支部総会講演会講演論文集 （一般社団法人 日本機械学会）  2021 （ 0 ） 10A15 2021年

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<p>The effects of co-doping in phosphors and the use of co-doped phosphors to extend the temperature measurement range were experimentally investigated in terms of the lifetime method. Such effects can be evaluated by comparing the single and double luminescent centers. In this study, YAG:Tb, YAG:Cr and YAG:Cr,Tb were prepared by sol-gel method and the luminescence intensity was measured under excitation by the 4^th harmonic of Nd:YAG laser. In order to improve the temperature measurement performance of YAG:Cr,Tb, it is desirable to divide it into two wavelength regions with a threshold around 600 nm, and to switch between the two regions depending on the temperature range when performing temperature measurement by the lifetime method. The absolute lifetime sensitivity <i>S_A</i> is a suitable index to use when dividing the temperature region into two regions, resulting in switching at around 800 K. The lifetime of the Cr-derived luminescence is slightly longer, while that of the Tb-derived luminescence is about 10 times shorter.</p>

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リーンバーンSIエンジンにおけるノッキング検出精度向上に関する研究

岡田 力也, 安武 優希, 御代川 慎司, 富所 拓哉, 横森 剛

日本機械学会関東支部総会講演会講演論文集 （一般社団法人 日本機械学会）  2021 （ 0 ） 10A16 2021年

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<p>The purpose of this study was to improve the accuracy of knock detection for lean burn SI engines. In this study, we conducted an experiment to observe autoignition in an engine cylinder using a borescope and a high-speed camera under an air excess ratio of 2.1. In addition, the resonance frequency of each vibration mode by knocking and the knock intensity were also calculated from the in-cylinder pressure history. Autoignition was optically observed in all cycles with a knock intensity of more than 20 kPa or more, and in some cycles with that of less than 20 kPa. We compared the vibration caused by combustion and it caused by autoignition. As a result, by distinguishing between the vibration caused by combustion and it caused by autoignition using window functions, a knocking cycle that could not be detected by the conventional index was detected.</p>

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Characteristics of counterflow premixed flames with low frequency composition fluctuations

Tomidokoro T., Yokomori T., Im H., Ueda T.

Combustion and Flame （Combustion and Flame）  212   13 - 24 2020年02月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  00102180

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© 2019 The Combustion Institute The response of laminar methane/air counterflow premixed flames under sinusoidal equivalence ratio oscillation was investigated numerically. The timescales of the oscillation were chosen to be sufficiently longer than the flame timescale so that the flame responds quasi-steadily. The response of periodically stratified flame (SF) with a detailed reaction mechanism exhibited the “back-support” effect, in that the consumption speed Sc response deviated increasingly from Sc of steady homogeneous flames (HFs) at higher oscillation frequencies. It was shown that even when the imposed oscillation timescale is much longer than the flame timescale, the flame response can still be delayed under a sufficiently large equivalence ratio gradient. Subsequently, the above results were compared with those obtained with a global four-step mechanism that omits back-diffusion radicals into the reaction zone. As a result, SFs with the global mechanism displayed a much smaller back-support effect in both lean and rich mixtures. Further analysis with modified diffusion coefficients revealed the dominant roles of H2 and radical species diffusion in inducing the back-support effect. Contrary to the previous findings, variations in burned gas temperature were found to play a negligible role in modifying Sc. Additionally, the hysteresis of the back-support effect under periodical stratification was found to be more prominent on the richer side because of the presence of a larger H2 pool.

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Precision evaluation of phosphors for the lifetime method in phosphor thermometry

Kazuki Tsuchiya, Kento Sako, Naohiro Ishiwada, and Takeshi Yokomori

Measurement Science and Technology （Measurement Science and Technology）  accepted （ 6 ）  2020年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  09570233

　概要を見る

© 2020 IOP Publishing Ltd. The precision of the lifetime method in phosphor thermometry was examined in terms of the uncertainty in temperature prediction. Such uncertainty can be estimated using the rate of change in lifetime with temperature (lifetime sensitivity) and the uncertainty in measured lifetime. This uncertainty depends on phosphorescence characteristics such as phosphorescence intensity and lifetime decay shape. In this study, we proposed a method of calculating uncertainties in measured lifetimes by the estimated regression coefficients in measured decay signals of phosphors. To demonstrate this evaluation, the uncertainties in the predicted temperatures of some common phosphors (MFG, GGG:Cr, Y2O3:Eu) were calculated. Consequently, the temperature predictions by the lifetime method with MFG, GGG:Cr, and Y2O3:Eu showed high precision at about 800 K, 700 K, and 900 K, respectively. This method of evaluating precision by using both lifetime sensitivity and uncertainty in lifetime helps to improve the appropriate use of phosphors for the lifetime method in phosphor thermometry.

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天然ガスの組成変化を伴うブンゼン火炎の応答とその制御

梅沢 修一, 石橋 卓也, 岡本 倫一, 横森 剛, 植田 利久

日本機械学会論文集 （一般社団法人 日本機械学会）  86 （ 884 ） 19 - 00432-19-00432 2020年

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<p>This study investigated experimentally a response of premixed Bunsen flame to transient change in a fuel composition and a method to control the variation. Fuel mixtures were composed of methane, ethane and propane. The volumetric fraction of methane was varied from 92 % to 76 % by 4 % and the ethane/propane ratio was 5. Transition time of the fuel composition was 1, 5, 10 and 20 s. Flow velocity and the equivalence ratio were 0.8 m/s and 0.85 respectively before the transition. Channel length <i>L</i> between the merging point of fuels and the point of air was 0, 500, 1000, 1500 mm. The motion of flame was recorded by a high-speed video camera at 60 fps. The experiment was conducted under the fuel flow rate constant and the equivalence ratio constant conditions. In the former condition, the flame height varied almost linearly not depending on the conditions. In the latter condition, variation of the steady flame height was smaller than the former condition. However, the unsteady flame height exceeded or fell below temporarily the steady flame height. This is due to the time lag between the transmission of fuel flow rate variation and fuel compositions variation. Therefore, considering this time lag, the experiment was conducted with a system which had a density meter to detect the fuel composition variation. The system controlled automatically the fuel flow rate. At long <i>L</i> and short transition time, there were some peaks in the flame height variation. It is considered that this is caused by the difference between the actual density and the output of the density meter due to Taylor dispersion and response time of the density meter. However, the flame height variation was smaller than the variation without control, and particularly at long transition time, the variation was suppressed sufficiently.</p>

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Response of a heat and moisture exchanger containing CaCl2 to the periodic change of flow direction

Okinaga Yoshihito, Murata Makoto, Ueda Toshihisa, Yokomori Takeshi

MECHANICAL ENGINEERING JOURNAL （一般社団法人 日本機械学会）  7 （ 1 ） 19 - 00335-19-00335 2020年

共著,  ISSN  2187-9745

　概要を見る

<p>The characteristics of a medical heat and moisture exchanger with filter (HMEF) that contained polyurethane sponges and CaCl₂ were investigated experimentally and model analysis was performed. Variations in the temperature and humidity were measured. Saturated air at 37 °C simulating exhalation and dry air at 26 °C simulating inhalation were fed alternatively through the HMEF in opposite directions. The period was set as 256 s, 64 s, 16 s and 4 s. When the period was long (256 and 64 s), the polyurethane sponges and CaCl₂ played an important role in condensation and evaporation of water and the amplitudes of the temperature variation was so large that it overshot the input condition. When the period was shortened (4 s), the amplitudes of the temperature and humidity variations decreased and the relative humidity of the patient side of the HMEF gradually reached that of the exhalation conditions. This suggests that the characteristic times of condensation and evaporation were longer than that of the respiration (<b>τ_b</b> = 4 s). In other words, the unsteady effect is important for the condensation and vaporization mechanism of HMEF. The mechanism was supported by the model analysis. In addition, comparing the results of the experiments and model analysis elucidated the effect of the connecting pipe, which corresponds to the dead space effect in clinical use.</p>

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Thermal efficiency improvement of super-lean burn spark ignition engine by stratified water insulation on piston top surface

Nagasawa T., Okura Y., Yamada R., Sato S., Kosaka H., Yokomori T., Iida N.

International Journal of Engine Research （International Journal of Engine Research）  accepted （ 5 ） 1421 - 1439 2020年

研究論文（学術雑誌）, 共著,  ISSN  14680874

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© IMechE 2020. In order to improve thermal efficiency of spark ignition engine under super-lean burn conditions (excess air ratio (Formula presented.)), thermal stratification technique by in-cylinder water injection toward piston surface (stratified water insulated combustion architecture), in which low temperature water vapor layer is formed on the surface, is proposed. From the water spray visualization using the optically accessible engine, injected water is distributed near the piston top surface at ignition timing and thermal stratification can be achieved in the case that water injection timing (SOIw) is set at earlier stage of a compression stroke. In addition, heat flux on the piston surface measured at the same time is reduced by water injection. The 0.5-L single-cylinder engine test at λ = 2.0 at a constant ignition timing also shows that water injection at earlier stage of a compression stroke makes it possible to mitigate knock without significant increase in combustion instability. On the other hand, part of water is distributed near the spark plug at ignition timing with the water injection at SOIw = −60 °ATDC, resulting in unstable combustion. In addition, the engine test at λ = 2.0 and water/fuel ratio(W/F) = 18% shows that knock mitigation by water injection enables spark advance and following combustion enhancement. As a result, combustion period becomes short and cooling loss decreases, followed by the 1.0-pt improvement of gross indicated thermal efficiency. Moreover, the engine can be operated at minimum spark advance for best torque by increasing W/F up to 35%. Finally, stratified water insulated combustion architecture concept is applied at λ = 1.9 with a higher compression ratio of 17, showing that water injection at SOIw = −120 °ATDC and W/F = 50% enables minimum spark advance for best torque operation, and remarkably high gross indicated that thermal efficiency of 52.63% can be achieved with a sufficiently low knock level and coefficient of variation of indicated mean effective pressure.

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Development of cycle-to-cycle variation of the tumble flow motion in a cylinder of a spark ignition internal combustion engine with Miller cycle

Matsuda M., Yokomori T., Shimura M., Minamoto Y., Tanahashi M., Iida N.

International Journal of Engine Research （International Journal of Engine Research）  22 （ 5 ） 1512 - 1524 2020年

共著,  ISSN  14680874

　概要を見る

© IMechE 2020. Reducing the cycle-to-cycle variation in an engine is a key to expanding the operational limits of high-efficiency engines such as lean-burn engines. The cycle-to-cycle variation of the engine output is caused by unstable combustion and is especially induced by the cycle-to-cycle variation of the in-cylinder flow. This investigation aims to clarify how the cycle-to-cycle variation of in-cylinder flow develops during intake and compression strokes. To achieve this aim, 12 kHz time-resolved particle image velocimetry measurements were conducted on the symmetrical vertical plane in a four-valve, four-stroke optically accessible engine. This study focuses on the relationship between the flow at the plug position at the ignition timing and the flow distribution in the intake and compression stroke. Correlation map analysis reveals this relationship, and some flow distributions are extracted. The fluctuations in the flow distribution induce the cycle-to-cycle variation of the flow direction at the plug position at the ignition timing, the position of the stagnation plane between the intake flow from the intake valves and the upper side of the tumble vortex, the strength of the blowback flow into the intake port generated by the Miller cycle, and the position of the tumble vortex in the late compression stroke. The flow distributions extracted by the correlation map analysis clearly change between cycles. These results also suggest that correlation map analysis is an effective way to elucidate the factors that induce the cycle-to-cycle variation of the in-cylinder flow.

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A computational analysis of strained laminar flame propagation in a stratified CH<inf>4</inf>/H<inf>2</inf>/air mixture

Tomidokoro T., Yokomori T., Ueda T., Im H.G.

Proceedings of the Combustion Institute （Proceedings of the Combustion Institute）  38 （ 2 ） 2543 - 2550 2020年

共著,  ISSN  15407489

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© 2020 The Combustion Institute. Propagation of a H2-added strained laminar CH4/air flame in a rich-to-lean stratified mixture is numerically studied. The back-support effect, which is known to enhance the consumption speed of a flame propagating into a leaner mixture compared to that into a homogeneous mixture, is evaluated. A new method is devised to characterize unsteady reactant-to-reactant counterflow flames under transiently decreasing equivalence ratio, in order to elucidate the influence of flow strain on the back-support effect. In contrast to the conventional reactant-to-product configurations, the current configuration is more relevant to unsteady stratified flames back-supported by their own combustion products. Moreover, since H2 distribution downstream of the flame is known to play a crucial role in back-supported CH4/air flames, the influence of H2 addition in the upstream mixture is examined. The results suggest that a larger strain rate leads to a larger equivalence ratio gradient at the reaction zone through increased flow divergence, which amplifies the back-support. Meanwhile, since H2 addition in the upstream mixture does not affect the downstream H2 content, the relative increase in the consumption speed, i.e. the back-support, is suppressed with larger H2 addition. Especially, when the upstream H2 content decreases with the equivalence ratio, the H2 preferentially diffuses toward the unburned gas, which mitigates H2 accumulation in the preheat zone and further weakens the back-support.

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A new pattern of flame/flow dynamics for lean-premixed, low-swirl hydrogen turbulent jet flames under thermoacoustic instability

Shoji T., Tachibana S., Suzuki T., Nakazumi Y., Yokomori T.

Proceedings of the Combustion Institute （Proceedings of the Combustion Institute）  38 （ 2 ） 2835 - 2843 2020年

研究論文（学術雑誌）, 共著,  ISSN  15407489

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© 2020 The Combustion Institute. Published by Elsevier Inc. This paper presents a phenomenological investigation of a new pattern of lean-premixed hydrogen-flame and flowfield dynamics under thermoacoustic instabilities (TIs) observed inside a low-swirl combustor (LSC) with two combustion chamber lengths of 300 and 500 mm. In this study, the initial bulk inlet velocity was set to V m = 15 m/s. The fuel flow rate was linearly increased while the air flow rate was kept constant, causing a transition from stable operation to TI. Simultaneous time-resolved electronically excited hydroxyl radical (OH *) chemiluminescence imaging and two-dimensional particle image velocimetry were performed along with pressure-fluctuation measurements to investigate spatiotemporal relationships between fluctuating quantities, i.e., OH * chemiluminescence, velocity fields, and pressure, before and after TI onset. A typical TI pattern characterized by a lifted, inverted conical flame caused by diverging, decelerating flow near the injector exit was observed in the long combustor. In contrast, the flame/flow dynamics pattern under TI in the short combustor had strong pressure oscillations and anomalous LSC flame structures which were characterized by a radially flat flame region and counter-rotating vortex pair (CVP) flame structures. In this case, the radial profile of the axial velocity assumed an atypical top-hat-like shape. This feature resulted in thermoacoustic coupling that satisfied the Rayleigh criterion over an almost entirely flat flame region and further strengthened the TI. Thermal expansions of CVP structures served as "converging nozzles" constricting the central flow region. Periodic appearances of this Venturi-like effect caused an alternating diverging (decelerating) and converging (accelerating) flowfield, with a significant peak-to-peak velocity-oscillation amplitude of 15 m/s, equivalent to V m . These pioneering observations regarding LSCs provide further insights into TI mechanisms in hydrogen-fueled gas turbine combustors.

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Effects of flame behaviors on combustion noise from lean-premixed hydrogen low-swirl flames

Shoji T., Iwasaki Y., Kodai K., Yoshida S., Tachibana S., Yokomori T.

AIAA Journal （AIAA Journal）  58 （ 10 ） 4505 - 4521 2020年

研究論文（学術雑誌）, 共著,  ISSN  00011452

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© 2020 by Takeshi Shoji, Yuki Iwasaki, Kato Kodai, Seiji Yoshida, Shigeru Tachibana, and Takeshi Yokomori. This experimental study explored the influence of global/local flame behaviors on direct combustion noise produced by a lean-premixed gaseous H2 ∕air low-swirl turbulent jet flame, with a focus on the mechanism resulting in characteristic peaks in combustion noise spectra. Ten kilohertz OH chemiluminescence and OH planar laser-induced fluorescence (OH-PLIF) imaging were used to study the spatiotemporal evolution of heat release and flame structure fluctuations, respectively, whereas 2-D particle image velocimetry (2-D PIV) measurements at 4 Hz were applied to study the mean-based relation between the velocity/vorticity fields and flame structures. Pressure and global heat release fluctuation measurements carried out alongside these optical diagnostics revealed pronounced double peaks in both combustion noise and global heat release fluctuation spectra at global equivalence ratios of ϕ ≥ 0.45. Spectral proper orthogonal decomposition of the OH chemiluminescence and OH-PLIF images revealed that the first peak in the noise spectra to be caused by flame oscillations over nearly the entire flame region, whereas the secondary peak was attributed to periodically generated vortical flame structures near the downstream side of the flame boundary. The 2-D PIV results suggest that vortical flame structures are likely generated by the interaction between the flame and the inner/outer shear layers.

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Effects of flame structures on direct combustion noise produced by lean-premixed h<inf>2</inf> /air low-swirl jet flames

Shoji T., Iwasaki Y., Kodai K., Yoshida S., Tachibana S., Yokomori T.

AIAA Scitech 2020 Forum （AIAA Scitech 2020 Forum）  1 PartF 2020年

研究論文（国際会議プロシーディングス）, 共著,  ISSN  9781624105951

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© 2020, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. This experimental study explored the influence of flame structural characteristics on direct combustion noise produced by a lean-premixed gaseous H2 /air low-swirl turbulent jet flame, with a focus on the mechanism resulting in characteristic peaks in combustion noise spectra. Ten-kHz OH* chemiluminescence and OH planar laser-induced fluorescence (OH-PLIF) imaging were used to study the spatiotemporal evolution of heat release and flame structure fluctuation, respectively, while two-dimensional particle image velocimetry (2D-PIV) measurements at 4 Hz were used to study the mean-based relation between the velocity/vorticity fields and flame structures. Pressure and global heat release fluctuation measurements carried out alongside these optical diagnostics revealed pronounced double peaks in both combustion noise and global heat release fluctuation spectra at global equivalence ratios of ϕ ≥ 0.45. Spectral orthogonal decomposition of the OH* chemiluminescence and OH-PLIF images revealed the first peak in the noise spectra to be caused by flame oscillations over nearly the entire flame region, while the secondary peak is attributed to periodically generated vortical flame structures near the flame boundary. The 2D PIV results suggest that vortical flame structures are probably generated by the interaction between the flame and the inner/outer shear layers.

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高速度OH-PLIF計測を用いたリーンバーンガソリンエンジンにおける初期火炎伝播の解析

松田 昌祥, 長島 朋来, 横森 剛, 志村 祐康, 店橋 護

熱工学コンファレンス講演論文集 （一般社団法人 日本機械学会）  2020 （ 0 ） 0185 2020年

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<p>This paper describes the ignition and early flame propagation in a high-tumble SI IC engine under super lean-burn condition (excess air ratio (λ) of 2.0). To elucidate the detail process, a high-tumble optically-accessible SI IC engine operating at super lean and stoichiometric conditions were diagnosed by time-resolved OH-PLIF measurements. The engine was operated 2000 rpm with a port fuel injection of isooctane. The cross-sectional imaging of OH distribution was achieved at 12 kHz resulting in a temporal resolution of 1° crank angle at 2000 rpm. The results show that the OH radical is generated without any heat release by the spark discharge during approximately 15 ° crank angle after ignition timing in the super-lean condition. The OH distribution of these crank angles are scatted into small islandlike areas, and then subsequent flame propagation occurs.</p>

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燐光体を利用した温度計測の基礎と原理

横森 剛, 石和田 尚弘

日本燃焼学会誌 （一般社団法人 日本燃焼学会）  62 （ 201 ） 234 - 241 2020年

学位論文（博士）, 共著,  ISSN  1347-1864

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<p>Accurate and reliable temperature measurements are crucial to improve the thermal efficiency and optimize the design of products because temperature is an important parameter to understand heat conduction, convention, radiation, and chemical reactions. The emission properties of phosphors are sensitive to temperature, hence, phosphor thermometry can make remote temperature sensing. Accordingly, phosphor thermometry has received considerable attention as a versatile alternative to conventional temperature measurement techniques. This article describes the principles and fundamental aspects of phosphor thermometry, that is, principles of luminescence, temperature dependences of luminescence characteristics and how to use those dependence characteristics such as life time method and spectral intensity ratio method.</p>

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タンブル流強化ガソリンエンジンにおける高速マイクロPIVとMEMS熱流束センサの同時計測

横山 瑛士, 鎌田 慎, 志村 祐康, 中別府 修, 横森 剛, 店橋 護

熱工学コンファレンス講演論文集 （一般社団法人 日本機械学会）  2020 （ 0 ） 0071 2020年

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<p>In order to understand the effect of velocity boundary layer on the heat loss in a tumble enhanced engine, simultaneous measurements of high-speed microscopic particle image velocimetry (PIV) near the piston top and a micro electro mechanical systems (MEMS) heat flux sensor on the piston surface was conducted in the motored optical engine with enhanced tumble flow. This engine was rotated at2000 rpm. Experimental results show the correlation between the velocity fluctuation and the peak value of heat flux, and the correlation coefficient shows higher value at 0.50 mm from the piston wall rather than 0.27 mm and 0.12 mm.</p>

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タンブル流強化ガソリンエンジンにおけるピストン頂面近傍の流動と壁面熱流束の相関

中別府 修, 鎌田 慎, 横山 瑛士, 志村 祐康, 横森 剛, 店橋 護

熱工学コンファレンス講演論文集 （一般社団法人 日本機械学会）  2020 （ 0 ） 0192 2020年

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<p>Heat transfer inside an engine has been studied for improving thermal efficiency by mitigation of the cooling loss. Flow near a piston top and heat flux on it were simultaneously measured with a microPIV and a MEMS thin film sensor in a motoring mode of an optical engine. It was confirmed that averaged heat flux over -15~15 CA deg. showed a positive correlation to the normal flow fluctuation, and that the instantaneous wall heat flux showed obvious correlation to the instantaneous normal velocity at 0.5 mm above the wall with a time lag of 200 s level. Moreover, a combination analysis of the wall parallel velocity and FFT spectrum of the heat flux showed that the fluctuation in the heat flux is composed of temperature unevenness of several millimeter scale and eddy motion of several hundred micrometer.</p>

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Development of cycle-to-cycle variation of the tumble flow motion in a cylinder of an SI IC engine with Miller cycle

Masayoshi Matsuda, Takeshi Yokomori, Masayasu Shimura, Yuki Minamoto, Mamoru Tanahashi, Norimasa Iida

International Journal of Engine Research accepted 2020年

査読有り

Ignition Experiments by Nanosecond Repetitively Pulsed Discharges in Intense Turbulence for Super Lean Burn at Engine Condition

Uesugi K., Morii Y., Mukoyama T., Tezuka T., Hasegawa S., Nakamura H., Takana H., Maruta K., Yokomori T., Iida N.

SAE Technical Papers （SAE Technical Papers）   （ December ）  2019年12月

研究論文（学術雑誌）, 共著, 査読有り

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© 2019 SAE Japan and SAE International. Ignition by Nanosecond Repetitively Pulsed Discharges (NRPD) at EXponential Increase of Minimum Ignition Energy (MIE-EXI) region under super lean SI engine conditions was studied. Fundamental experiments were conducted with a turbulent ignition test chamber with twin counter-rotating fans. The MIE-EXI region by arc discharge appeared over 6500 rpm of fan speed. In the MIE-EXI region (7000 rpm), successful ignition was achieved by establishing coupled ignition kernels with NRPD at 15 kHz although ignition was unsuccessful at 1 kHz. Results show that ignition by NRPD has potential advantages for lean burn applications. Preliminary engine test results with NRPD were also demonstrated.

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Research of Fuel Components to Expand lean-limit in Super lean-burn condition

Naiki T., Obata K., Watanabe M., Yokomori T., Iida N.

SAE Technical Papers （SAE Technical Papers）   （ December ）  2019年12月

研究論文（学術雑誌）, 共著, 査読有り

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© 2019 SAE Japan and SAE International. The thermal efficiency of internal combustion engines can be improved dramatically with the right combination of engine technology and fuel technology. Super lean-burn technology is attracting attention as a means of boosting thermal efficiency. However, there is a limit to how lean a fuel-air mixture can be before combustion becomes unstable or misfire occurs. The authors evaluated the effects of various chemical compositions on the lean limit under super lean-burn conditions. By changing the composition of the fuel, it was possible to achieve excess air ratios of over 2.0, resulting in high thermal efficiency.

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Influence of ethanol blending on knocking in a lean burn SI engine

Kaneko K., Yasutake Y., Yokomori T., Iida N.

SAE Technical Papers （SAE Technical Papers）   （ December ）  2019年12月

研究論文（学術雑誌）, 共著, 査読有り

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© 2019 SAE Japan and SAE International. Lean burn is one method for improving thermal efficiency in spark ignition (SI) engines. Suppression of knocking provides higher thermal efficiency, and ethanol blending is considered an effective way to suppress knocking due to its high octane and high latent heat of evaporation. We investigate the effect of ethanol blending on knocking in an SI engine under lean operating conditions. The Livengood-Wu (LW) integral was performed based on ignition delay duration estimated from a zero-dimensional detailed chemical reaction calculation with pressure and temperature histories. Knocking was suppressed and thermal efficiency increased with ethanol-gasoline blending fuel, even at 0.5 equivalence ratio. Decrease in unburned gas temperature by latent heat of evaporation had a comparable influence on knocking suppression, which was supported by LW integral analysis.

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同軸型薄膜温度センサを用いた内燃機関の燃焼室壁面における熱流束解析手法及び精度に関する研究

石井大二郎, 三原雄司, 横森剛

日本機械学会論文集 （日本機械学会）  85 （ 879 ） 19-00262 - 00262-19-00262 2019年11月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  2187-9761

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<p>In order to improve thermal efficiency of automobile engine, it is necessary to reduce the cooling loss. A method for analyzing local cooling loss (heat flux) using coaxial type thin film temperature sensor has been developed. Recently, results of heat flux analysis using the sensor composed of thermocouple materials standardized based on ANSI and JIS have been reported, but structure and measurement accuracy of its sensor are not clear enough. In this study, the measurement accuracy of sensor A composed of K type materials and sensor B whose body is combustion chamber material (aluminum alloy) was compared using numerical analysis (two-dimensional coordinate heat conduction equation when the sensor is embedded in combustion chamber). As a result, it was important to use same material as combustion chamber for sensor body to measure wall surface instantaneous temperature with high accuracy. Additionally, results of one-dimensional (axial direction) heat flux analysis when the material of the combustion chamber and the material of the sensor body are different had error, it was considered to effect of heat flow (temperature difference) in radial direction due to different thermal conductivity. Therefore, it was confirmed that newly proposed two-dimensional heat flux analysis method using temperature distribution in axial and radial direction can analyze more accurately than one-dimension. These numerical analysis results showed same tendency as measured verifications results.</p>

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Influence of spark discharge characteristics on ignition and combustion process and the lean operation limit in a spark ignition engine

Tsuboi S., Miyokawa S., Matsuda M., Yokomori T., Iida N.

Applied Energy （Applied Energy）  250   617 - 632 2019年09月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  03062619

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© 2019 Elsevier Ltd Lean combustion technologies have been investigated to decrease the heat loss of spark ignition engines. However, as the excess air ratio approaches the lean operation limit, the cycle-to-cycle variation of combustion becomes an obstacle to improving thermal efficiency. This paper discusses the influences of spark discharge characteristics, such as discharge current and spark-shortening phenomena, on the ignition and combustion process under lean conditions (excess air ratio (λ) of 1.8–2.3) to suppress the cycle-to-cycle variation of combustion and extend the lean operation limit. In this study, a customized inductive ignition system equipped with 20 conventional ignition coils was applied to enhance the ignition energy. The discharge interval between each coil unit was controlled to change the discharge current and duration. The results show that the in-cylinder discharged energy increased with the discharge interval. The cycle-to-cycle variation of combustion was minimized when the discharge interval was 0.4 ms, and consequently, the lean operation limit was extended to an excess air ratio (λ) of 2.1. The discharge waveforms indicated that the longer discharge interval could promote spark-shortening phenomena such as re-strike due to the lower discharge current. Finally, in-cylinder photographs of ignition and combustion process showed that the flame kernel formation could be promoted by the repetition of spark-shortening phenomena such as re-strike, as well as by the high elongation of the spark channel.

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Effect of simultaneous velocity and equivalence ratio oscillations on a laminar premixed stagnating flame

Niwa Y., Okamoto M., Yokomori T., Ueda T.

Experiments in Fluids （Experiments in Fluids）  60 （ 7 ）  2019年07月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  07234864

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© 2019, Springer-Verlag GmbH Germany, part of Springer Nature. Abstract: The dynamics of a laminar premixed stagnating flame subjected to simultaneous velocity and equivalence ratio oscillations are investigated experimentally. A flame of premixed methane and air is formed in a wall-stagnating flow. The oscillations of velocity and equivalence ratio are imposed independently by two sets of dual cylinder–piston oscillators. To impose the equivalence ratio oscillation, methane/air mixtures with equivalence ratios of ϕ= 1.0 and 0.4 are supplied to different cylinder–piston units. The pistons move in anti-phase and create a sinusoidal equivalence ratio oscillation while keeping the volume flow rate constant. To impose the velocity oscillation, a mixture with ϕ= 0.7 is supplied to the single unit of another oscillator. The phase difference between the two oscillations is set by changing the relative position of the pulley teeth of the two oscillators. The oscillator frequency is varied between 2 and 20 Hz, meaning that the oscillation wavelengths are much longer than the flame thickness. When frequencies of the velocity and equivalence ratio fluctuations are in a quasi-steady state condition, the flame motion is affected independently by velocity oscillation and equivalence ratio oscillation and the linear-superposition assumption can be applied. When the velocity and equivalence ratio oscillation frequencies are increased and exceed the transition frequency from the quasi-steady state to unsteady state, the flame motion gradually deviates from linear-superposition assumption. This is due to the variations in the unsteady molecular diffusion and the back-support effect.

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Applicability of Dy-doped yttrium aluminum garnet (YAG:Dy) in phosphor thermometry at different oxygen concentrations

Ishiwada N., Tsuchiya K., Yokomori T.

Journal of Luminescence （Journal of Luminescence）  208   82 - 88 2019年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  00222313

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© 2018 Elsevier B.V. Phosphor thermometry is a method used to measure temperature based on the temperature-dependent phosphorescence of phosphors and elucidate heat transfer phenomena, such as high-temperature gas flow. Although various rare earth-doped thermographic phosphors are in use, the effect of oxygen concentration on their phosphorescence has not been sufficiently explored. We explore herein the applicability of Dy-doped yttrium aluminum garnet (YAG:Dy), a well-known rare earth-doped phosphor with temperature sensitivity above 1000 K, in phosphor thermometry at different oxygen concentrations. A third-harmonic Nd: YAG laser excited the sample. Phosphorescence was measured using a photomultiplier tube for lifetime detection. A spectrometer was used to detect the intensity ratio between two emission lines. The chamber was filled with a nitrogen–oxygen mixture with a controlled concentration. The phosphorescence intensity ratio depended on temperature over a wide temperature range and varied with the oxygen concentration, especially above 1000 K. The YAG:Dy lifetimes could be detected over the entire temperature range and remained constant up to 1000 K. In addition, the lifetimes decreased with the increasing oxygen concentration, especially above 1000 K, confirming the oxygen quenching effect. Consequently, YAG:Dy is confirmed to be sensitive to oxygen concentration for determining the intensity ratio and lifetime, especially above 1000 K.

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A Cycle-to-Cycle Variation Extraction Method for Flow Field Analysis in SI IC Engines Based on Turbulence Scales

Matsuda M., Yokomori T., Minamoto Y., Shimura M., Tanahashi M., Iida N.

SAE Technical Papers （SAE Technical Papers）  2019-January （ January ）  2019年01月

研究論文（学術雑誌）, 共著, 査読有り

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© 2019 SAE International. All Rights Reserved. To adhere to stringent environmental regulations, SI (spark ignition) engines are required to achieve higher thermal efficiency. In recent years, EGR (exhaust gas recirculation) systems and lean-burn operation has been recognized as key technologies. Under such operating conditions, reducing CCV (cycle-to-cycle variation) in combustion is critical to the enhancement of overall engine performance. Flow-field CCV is one of the considerable factors affecting combustion in engines. Conventionally, in research on flow fields in SI engines, the ensemble average is used to separate the measured velocity field into a mean component and a fluctuation component, the latter of which contains a CCV component and a turbulent component. To extract the CCV of the flow field, previous studies employed spatial filter, temporal filter, and POD (proper orthogonal decomposition) methods. Those studies used a constant- separation filter size for the whole crank angle, although the turbulence scales change rapidly during the intake and compression stroke processes. Hence the definition of filter size has some room to be explored in order to take account of these features. The objective of this research is to improve the method of separating the CCV component using turbulence scales. For this purpose, high-speed PIV measurement was conducted on the symmetrical vertical plane for an optical IC engine at repetition rates of 12 kHz (1 C.A. deg. resolution) for the whole in-cylinder area and 48 kHz (0.25 C.A. deg. resolution) for the plug position. The measured data were separated into CCV and turbulent components by using the proposed filter, whose size was selected adaptively considering the integral time scale of the turbulent flow. The effect of time resolution on the filter size was then elucidated.

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Study of a thermo-acoustic instability triggering in a low-swirl burner using simultaneous time-resolved acetone and OH-PLIF

Renaud A., Yokomori T., Tachibana S.

Proceedings of the Combustion Institute （Proceedings of the Combustion Institute）  37 （ 2 ） 2627 - 2633 2019年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  15407489

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A low-swirl burner operating in premixed mode with methane and air is studied using high-speed acetone and OH-PLIF and advanced post-processing methods. In a transient operating point where the equivalence ratio is slowly increased while keeping the bulk velocity constant, a thermo-acoustic instability is found to grow and generate large pressure fluctuations in the combustion chamber. The instability is maintained by bursts of flame in phase with the pressure fluctuation cycle. It is found that these bursts are amplified by the fact that the boundaries of the flame arms are fluctuating in phase. This phasing of the arms' boundaries is due to the change in flame speed coming from the increase of equivalence ratio.

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Micro particle image velocimetry investigation of near-wall behaviors of tumble enhanced flow in an internal combustion engine

Shimura M., Yoshida S., Osawa K., Minamoto Y., Yokomori T., Iwamoto K., Tanahashi M., Kosaka H.

International Journal of Engine Research （International Journal of Engine Research）  20 （ 7 ） 718 - 725 2019年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  14680874

　概要を見る

© IMechE 2018. A micro particle image velocimetry has been performed to investigate tumble enhanced flow characteristics near piston top surface of a motored internal combustion engine for three inlet valve open timing (−30, −15, 0 crank angle degrees). Particle image velocimetry was conducted at 340, 350 and 360 crank angle degrees of the end of the compression stroke at the constant motored speed of 2000 r/min. The measurement region was 3.2 mm × 1.5 mm on the piston top including central axis of the cylinder. The spatial resolution of particle image velocimetry in the wall-normal direction was 75 µm and the vector spacing was 37.5 µm. The first velocity vector is located about 60 µm from the piston top surface. The micro particle image velocimetry measurements revealed that the ensemble-averaged flow near the piston top is not close to the turbulent boundary layer and rather has tendency of the Blasius theorem, whereas fluctuation root-mean-square velocity near the wall is not low. This result shows that revision of a wall heat transfer model based on an assumption of the proper characteristics of flow field near the piston top is required for more accurate prediction of heat flux in gasoline engines.

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Influences of spark discharge characteristics on ignition and combustion process in lean-burn SI engine

Tsuboi S., Miyokawa S., Matsuda M., Yokomori T., Iida N.

12th Asia-Pacific Conference on Combustion, ASPACC 2019 （12th Asia-Pacific Conference on Combustion, ASPACC 2019）  2019年

研究論文（国際会議プロシーディングス）, 共著, 査読有り

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© Asia-Pacific Conference on Combustion, ASPACC 2019.All right reserved. Lean-burn SI engines have been investigated to decrease the heat loss, such as the cooling loss and the pumping loss. However, as excess air ratio approaches the lean operation limit, the cycle-to-cycle variation (CCV) of SI combustion becomes an obstacle to stable operation. This study reports the effects of spark discharge characteristics, such as discharge current and spark-shortening phenomena, on the CCV of SI combustion under lean operation (excess air ratio = 1.8 - 2.3). An enhanced ignition system equipped with 20 ignition coils was utilized in this study. In the experiment, the discharge interval between each coil unit was modified to change the discharge current and duration. The results showed that the CCV of combustion was suppressed with the discharge interval, and the lean operation limit was extended to = 2.1. Observations of in-cylinder photographs suggest that the repetition of spark-shortening phenomena promoted the flame kernel formation.

On the evaluation of stratification effect on unsteady counterflow flames under mixture composition oscillation

Tomidokoro T., Yokomori T., Im H., Ueda T.

12th Asia-Pacific Conference on Combustion, ASPACC 2019 （12th Asia-Pacific Conference on Combustion, ASPACC 2019）  2019年

研究論文（国際会議プロシーディングス）, 共著, 査読有り

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© Asia-Pacific Conference on Combustion, ASPACC 2019.All right reserved. Although an extensive study has been conducted to elucidate the effect of equivalence ratio gradient on flame characteristics, some disagreements regarding the mechanism of the stratification effect exist. This may be attributed to differences in the flame properties used to evaluate the stratification effects. The present study evaluated the magnitude of the stratification effects with various flame properties used previously, and compared their response to mixture composition oscillations. The response of displacement speed was affected by unsteady gas expansion, while the response of consumption speed directly represented the variation in the reaction rate. The response of peak heat release rate provided a better representation of the response of fuel consumption rate than the global heat release rate, because it measures the local characteristics at the reaction zone and does not include heat release variations in the wake of the flame. However, the peak heat release rate overestimates the magnitude of the stratification effect due to additional variation in the heat release from H2 oxidation reaction, which is caused by increase/decrease in the H2 diffusion from the burned side.

Quantitative prediction of fluid flow patterns with gel reaction in a circular flow pipe

Yamaguchi M., Yokomori T., Ueda T.

Journal of Chemical Engineering of Japan （Journal of Chemical Engineering of Japan）  52 （ 7 ） 593 - 598 2019年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  00219592

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Copyright © 2019 The Society of Chemical Engineers, Japan Fluid flow patterns with a gel reaction in a circular flow pipe are investigated experimentally. Solutions of 10 mass% polyvinyl alcohol (PVA) and 3 mass% borax are used as the working fluids. The flow channel consists of a transparent main flow pipe and a transparent branch flow pipe that is connected vertically to the main flow pipe. The solution of 10 mass% PVA flows in the main flow pipe under steady-state conditions. The Reynolds number (Rem) based on the mean velocity and the diameter of the main flow pipe is less than 30. The borax solution is colored with blue dye to visualize the flow patterns and is injected once only from the branch flow pipe. The experimental results show three distinct flow patterns, namely, capsule, capsule+stretched, and capsule+stretched+fingering flow. Rem and the ratio of the volume flow rate (β) are used to predict quantitatively the flow patterns with gel reaction. The results show that, in the region in which β is less than unity, capsule flow forms and β is the governing parameter. In the region in which β is greater than unity, Rem is dominant for determining the flow pattern with gel reaction.

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Effect of surfactant on the methane hydrate combustion

Ueda T., Mizuochi K., Yokomori T.

12th Asia-Pacific Conference on Combustion, ASPACC 2019 （12th Asia-Pacific Conference on Combustion, ASPACC 2019）  2019年

研究論文（国際会議プロシーディングス）, 共著, 査読有り

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© Asia-Pacific Conference on Combustion, ASPACC 2019.All right reserved. Effect of surfactant, sodium dodecyl sulfate (SDS) on the methane hydrate combustion has been investigated experimentally. Water solution of 0-2300 ppm SDS and methane are used to form the methane hydrate with SDS. Methane hydrate of 30 g was placed in a petri dish with 100 mm inner diameter and 10mm depth. The upper surface is opened to the air and is flushed. The temperature at 1.5 mm below from the upper surface of the petri dish along the centerline was measured by a K-type thermocouple. The petri dish is placed in a vertical flow channel where the honeycomb is installed to stabilize the upward flow due to the natural convection by combustion. When the temperature reaches the ignition temperature, the hydrate is ignited at the center by a pilot burner. The flame motion is recorded by a high-speed video camera with 125 fps and the temperature data from the thermocouple is stored in a data logger. In the case of the methane hydrate with SDS, a large amount of soapy bubble was formed shortly after the ignition over the hydrate surface. The bubbles decrease the heat from the flame to the hydrate surface and then the flame is weakened and extinguished faster than the pure methane hydrate. The bubbles stifle to form an anomalous preservation zone and then the distinct decrease in the flame propagation speed is not observed.

SIP「革新的燃焼技術」ガソリン燃焼チームの研究成果―高効率ガソリンエンジンのためのスーパーリーンバーン研究開発―

飯田 訓正, 横森 剛, 津江 光洋, 北川 敏明, 小酒 英範, 三好 明, 森吉 泰生

日本燃焼学会誌 （一般社団法人 日本燃焼学会）  61 （ 197 ） 178 - 192 2019年

学位論文（博士）, 共著,  ISSN  1347-1864

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<p>The "Innovative Combustion Technology" program, a national project is established under the Cabinet Office, Government of Japan as a part of the" Cross-ministerial Strategic Innovation Promotion Program (SIP)". The "Gasoline Combustion Team" is one of teams of the "Innovative Combustion Technology" program.</p><p>The "Gasoline Combustion Team" is comprised of Keio University as a Leader university and 29 universities as a Cluster university. Upon agreement with the Japan Science and Technology Agency (JST), we have been conducting the research on the "Super-Lean Burn for Gasoline Engines" with a support of the Research Association of Automotive Internal Combustion Engines (AICE) under the strong industry, academia and government collaboration.</p><p>This paper introduces both scientific and technological approaches to innovative combustion technologies to realize the "Super- Lean Low Temperature Combustion", targeting a thermal efficiency of 50%.</p>

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Investigation on flame developments in a SI engine with tumble flow using OH PLIF

Shimura M., Siddhartha K., Moronuki T., Minamoto Y., Yokomori T., Tanahashi M.

International Heat Transfer Conference （International Heat Transfer Conference）  2018-August   IHTC16-23975 - 1664 2018年08月

研究論文（国際会議プロシーディングス）, 共著, 査読有り,  ISSN  2377424X

　概要を見る

© 2018 International Heat Transfer Conference. All rights reserved. The present study is aimed at exploring the spatial and temporal development of the flame kernel using OH planar laser-induced fluorescence (PLIF) in a single cylinder optical SI engine with a gasoline surrogate fuel. A tumble enhancing intake port is used for the sake of improvement of ignition and flame propagation. The engine speed was set to 2000 rpm through the experiments. Equivalence ratio is changed from 1.0 to 0.6. With decrease of equivalence ratio, ignition timing is changed to be earlier for appropriate combustion. From the preliminary measurement using particle image velocimetry (PIV), it is found that the cycle-cycle variations of main stream direction of tumble flow at the ignition point are prone to be large in approaching to top dead center in the compression stroke, which significantly affects characteristics of flame and in-cylinder pressure developments. From results of OH PLIF in different crank angle degrees (CAD) after ignition, characteristics of flame behavior are investigated with considering temporal evolution of in-cylinder pressure and characteristics of discharge path. For the stoichiometric condition, overall flame locations are fluctuated by variations of main flow direction, while nevertheless the pressure evolves properly due to fast flame propagation. For the lean conditions, initial stage of flame kernel development has great influence on the completeness of whole combustion.

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Experimental Study of Thermo-Acoustic Instability Triggering in a Staged Liquid Fuel Combustor Using High-Speed OH-PLIF

A. Renaud, S. Tachibana, S. Arase, T. Yokomori

Journal of Engineering for Gas Turbines and Power （Journal of Engineering for Gas Turbines and Power）  140 （ 8 ） No. 081505 2018年05月

研究論文（学術雑誌）, 共著, 査読有り

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燃料組成の過渡的変化が予混合火炎の挙動に及ぼす影響

鈴木 貴士, 佐藤 衛, 梅沢 修一, 横森 剛, 植田 利久

日本機械学会論文集 （日本機械学会）  84 （ 857 ） 17-00168 - 00168-17-00168 2018年01月

共著, 査読有り

　概要を見る

<p>Flame height variations of a laminar stagnating premixed flame with gas component transition between fuel mixture A (methane:92%, ethane:6.7%, propane:1.3%) and B(methane:84%, ethane:13.3%, propane:2.7%), and between A and C (methane:76%, ethane:20.0%, propane:4.0%) are discussed. The estimation of the flame speed and the flame temperature of fuel mixtures A, B and C by the Chemkin-Pro show almost the same values for all fuel mixtures. In experiments, the transition between A and B and between A and C were performed. The transition time changes from 1 s to 10 s, keeping flow velocity and equivalence ratio constant at 0.8 m/s and 0.7 respectively. The flame position was measured by using images taken by a high speed camera with 125 fps. Two transition patterns are examined, keeping the total flow rate of premixed mixture constant. One is the constant flow rate transition, which changes the gas component, keeping the fuel mixture flow rate constant. The other is the constant equivalence ratio transition, keeping the equivalence ratio constant. In the case of the constant flow rate transition, the equivalence ratio changes which results in the variation in the flame speed, the flame temperature and the flame height. It means that the combustion state changes with the transition. On the other hand, in the case of the constant equivalence ratio transition, the flame speed, the flame temperature and the flame height keep almost the same state, which means that the gas component can be changed, keeping the combustion state the same.</p>

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PIVを用いたエンジン筒内の流動計測技術

横森 剛, 松田 昌祥

計測と制御 （公益社団法人 計測自動制御学会）  57 （ 5 ） 313 - 317 2018年

学位論文（博士）, 共著,  ISSN  0453-4662

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燃料組成の過渡的変化に対するブンゼン火炎の変動抑制

岡本 倫一, 石橋 卓也, 杉田 勝彦, 梅沢 修一, 横森 剛, 植田 利久

動力・エネルギー技術の最前線講演論文集 : シンポジウム （一般社団法人 日本機械学会）  2018 （ 0 ） B232 2018年

共著

　概要を見る

Responses of premixed laminar Bunsen flame to transient change in fuel gas composition has been investigated experimentally. Mixture of methane, ethane, and propane is used as a model of natural gas. The volumetric fraction of methane was varied from 92 % to 76 % by 4 %, keeping ethane/propane ratio 5 constant. Transition time of the fuel composition was changed from 1 to 20 sec. The flow velocity at the exit of the burner was 0.8 m/s. The distance between the fuel mixing point and the air and fuel mixing point L was changed from 0 to 1500 mm. A flame motion was recorded by a high speed video camera at 60 fps, and variation of the flame height was measured The flame height temporarily exceeded or fell below the steady flame height during the transition even though the equivalence ratio of mixture before and after the transition set the same. When a density meter was set in the flow channel to detect the fuel composition variation, the temporary flame height be suppressed.

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Evaluation of Dy-doped phosphors (YAG:Dy, Al<inf>2</inf>O<inf>3</inf>:Dy, and Y<inf>2</inf>SiO<inf>5</inf>:Dy) as thermographic phosphors

Ishiwada N., Fujii E., Yokomori T.

Journal of Luminescence （Journal of Luminescence）  196   492 - 497 2017年11月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  00222313

　概要を見る

© 2017 Elsevier B.V. Phosphor thermometry has been viewed as a promising method for non-contact temperature measurement. This article explores the temperature dependence of the Dy-doped phosphors: YAG: Dy, Al2O3:Dy, and Y2SiO5:Dy. The phosphors were energized at 355 nm from a 3rd-harmonic-generation Nd:YAG laser. The intensity of YAG:Dy was much stronger than the other phosphors, and the I458 nm/I497 nm intensity ratios had high temperature resolution over a wide range of temperatures. Although Al2O3:Dy and Y2SiO5:Dy had weaker intensity, the temperature resolution of intensity ratios was as substantial as YAG:Dy. The uncertainty in measured temperature of Dy-doped phosphors was evaluated using linearized error propagation theory, based on the noise-to-signal ratio and temperature sensitivity, revealing that the measurement uncertainty of YAG:Dy was less than the other two phosphors, and thus was the most reliable thermographic phosphor. In addition, the optimization of the bandpass filter combination was explored at each temperature range with YAG:Dy phosphor. Consequently, each temperature can be precisely measured by dividing the integrated intensity between 441 and 475 nm as a counter peak range and 476–500 nm as a main peak range. Thus, ideal bandpass filters are relatively constant throughout all temperatures.

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Investigation of Cycle-to-Cycle Variation of Turbulent Flow in a High-Tumble SI Engine

Masayoshi Matsuda, Takeshi Yokomori,Norimasa Iida

SAE Technical Papers （SAE）  2017-   2017-01-2210 2017年10月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0148-7191

　概要を見る

The thermal efficiency of a spark-ignition (SI) engine must be improved to reduce both environmental load and fuel consumption. Although lean SI engine operation can strongly improve thermal efficiency relative to that of stoichiometric SI operation, the cycle-to-cycle variation (CCV) of combustion increases with the air dilution level. Combustion CCV is caused by CCVs of many factors, such as EGR, spark energy, air-fuel ratio, and in-cylinder flow structure related to engine speed. This study focuses on flow structures, especially the influence of a tumble structure on flow fluctuation intensity near ignition timing. We measured the flow field at the vertical center cross section of an optically accessible high-tumble flow engine using time-resolved particle image velocimetry. There are many factors considered to be sources of CCV, we analyzed three factors: the intake jet distribution, distribution of vortex core position and trajectory of the fluid particle near the spark plug. To estimate the trajectory of fluid particle, the flow structure near the spark plug is tracked backward from the ignition timing to the intake stroke. The CCV of the fluid particle trajectory has two modes, and it is induced by the different of horizontal velocity component. The more detail study is needed to detect the cause of this two-mode behavior. Furthermore, the relationships between CCV factors were analyzed by correlation coefficient and multiple regression analysis. It was not confirm that the CCV of intake jet flow and the pressure wave affect directly the following CCV factors. The CCV of the flow field is mainly generated in the compression stroke. The key part for the CCV at ignition timing is not only the vortex core position, but also the area around the vortex core.

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気相燃焼ナノ粒子合成法における粒子成長のCQMOMを用いた数値シミュレーション

松下 晴樹, 瀧川 晃太郎, 横森 剛

微粒化 （日本液体微粒化学会）  26 （ 88 ） 49 - 55 2017年07月

共著, 査読有り,  ISSN  1341-6022

Experimental Study on Flow Characteristics with Gel Reaction in a Non-Element Mixer

Masaki Yamaguchi, Ryo Hagiwara, Takeshi Yokomori,Toshihisa Ueda

Journal of Chemical Engineering of Japan （Chemical Engineering of Japan）  50 （ 7 ） 485 - 491 2017年07月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-9592

　概要を見る

Flow characteristics with gel reaction of 10 mass% PVA and 3 mass% borax solutions in a Non-element mixer were experimentally investigated. The mixer consisted of a transparent main flow pipe and transparent branch flow pipes that were connected vertically to the main flow pipe. The PVA solution was supplied to the main flow pipe at a constant inlet pressure 20 kPa. The Reynolds number of the main flow (Re) was varied from 0.5 to 10.0. The borax solution was dyed blue to visualize the flow patterns and was injected periodically from one of the branch flow pipes at a mean speed of 40 mm/s. A pressure sensor was used to measure the pressure variation at 100 mm upstream from the first branch flow pipe. When Re was low, the borax periodically formed a capsule-like slug similar to those that occur in multiphase flows. As Re was increased, the borax capsule was stretched by the shear stress of the main flow and adhered to the upside wall of the mixer. At Re = 10.0, the pipe was prone to becoming blocked by excess gel product, which resulted in the pressure increasing to the inlet pressure of the system.

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乱流燃焼ダイアグラムを用いたスーパーリーンバーンSI エンジンにおける燃焼形態の検討

菅田 健志, 李 世埈, 横森 剛, 飯田 訓正

自動車技術会論文集 （自動車技術会）  48 （ 4 ） 801 - 806 2017年07月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0287-8321

Effect of a Transition in a Fuel Species Fraction on the Behavior of a Bunsen-Type Premixed Flame

Takuya Ishibashi, Takuya Tomidokoro, Takashi Suzuki, Shuichi Umezawa, Takeshi Yokomori, Toshihisa Ueda

Proceedings of the ASME Power Conference Joint with ICOPE-17 （ASME）  1   V001T04A039 2017年06月

研究論文（国際会議プロシーディングス）, 共著, 査読有り

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Experimental Study of Thermo-Acoustic Instability Triggering in a Staged Liquid Fuel Combustor using High-Speed OH PLIF

Antoine Renaud, Shigeru Tachibana, Shuta Arase, Takeshi Yokomori

Proceedings of ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition    GT2017-64102 2017年06月

研究論文（国際会議プロシーディングス）, 共著, 査読有り

Combined Effects of Spark Discharge Pattern and Tumble Level on Cycle-to-Cycle Variations of Combustion at Lean Limits

Dongwon Jung, Kosaku Sasaki, Kenji Sugata, Masayoshi Matsuda, Takeshi Yokomori, Norimasa

SAE Technical Paper （SAE）  2017- （ March ） 2017-01-0677 2017年03月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0148-7191

　概要を見る

Improving the thermal efficiency of spark ignition (SI) engine is strongly required due to its widespread use but considerably less efficiency than that of compression ignition (CI) engine. Although lean SI engine operation can offer substantial improvements of the thermal efficiency relative to that of traditional stoichiometric SI operation, the cycle-to-cycle variations of combustion increases with the level of air dilution, and becomes unacceptable. To improve the stability of lean operation, this study examines the effects of spark discharge pattern and tumble level on cycle-to-cycle variations of combustion at lean limits. The spark discharge pattern was altered by a custom inductive ignition system using ten spark coils and the tumble level was increased by a custom adapter installed in the intake port (tumble adapter). The results show that increased discharge energy by ten spark coils (without discharge offset) extends the lean limits with an improvement of indicated thermal efficiency (th), relative to that of stoichiometric operation. Furthermore, a combination of increased discharge energy and higher tumble level by tumble adapter makes it possible to allow stable operation at more extended lean limit, which is mainly attributed to shortening the duration of ST-to-CA5 and CA10-to-CA90. To examine the effect of spark discharge pattern on cycle-to-cycle variations of combustion at lean limits, the spark discharge pattern was altered for optimized combination of discharge energy and duration by adjusting the time offset between five discharges. The discharge offset of 0.25ms enables most stable ultra-lean operation, with COV of IMEPn less than 5% up to =2.0.

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Experimental Investigation of Unsteady Characteristics of the Low-Swirl Hydrogen-Air Turbulent Lean Premixed Flames

Shintaro Ogi, Shigeru Tachibana, Takeshi Yokomori

Proceedings of The 2016 Asia-Pacific International Symposium on Aerospace Technology （Japan Society for Aeronautical and Space Science）     APISAT-2016-N9-1 2016年10月

研究論文（国際会議プロシーディングス）, 共著

Quasi-steady state to non-steady state transition criterion of laminar stagnating lean premixed flame with fuel concentration oscillation

Daijiro Kawasaki, Kentaro Kashiwagi, Takeshi Yokomori, Toshihisa Ueda

Mechanical Engineering Letters （The Japan Society of Mechanical Engineers）  2   No.16-00374 2016年07月

研究論文（学術雑誌）, 共著, 査読有り

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Experimental study on a methanol auto-thermal reforming for compact reformer

Jun Ohtani, Takahiro Sakamoto, Masayoshi Wada, Hasan Mohd Faizal, Takeshi Yokomori, Toshihisa Ueda

Bulletin of the JSME, Mechanical Engineering Journal （The Japan Society of Mechanical Engineers）  3 （ 2 ） Paper No.15-00069 2016年04月

研究論文（学術雑誌）, 共著, 査読有り

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Experimental study on combustion of a methane hydrate sphere

Tomoki Yoshioka, Yuji Yamamoto, Takeshi Yokomori, Ryo Ohmura, Toshihisa Ueda

Experiments in Fluids （Springer）  56 （ 10 ） No.192 2015年11月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0723-4864

　概要を見る

The combustion behavior of a methane hydrate sphere under normal gravity is experimentally investigated. The initial diameter of the sphere is 20 mm. Variation in temperature at the center of the sphere (T-c) is measured with a K-type thermocouple at ignition temperatures (T-c,T-i) from 193 to 253 K at 20 K intervals. Variation in the near-surface temperature of the sphere (T-s) is measured at ignition temperatures (T-s,T-i) from 233 to 263 K at 10 K intervals. Two combustion phases are observed. When the hydrate is ignited, a stable flame envelope is formed around the sphere (phase 1). In phase 1, the surface of the sphere is dry. After a few seconds, water formed by dissociation of the methane hydrate appears on the surface and methane bubbles are formed by methane ejected from inside the sphere (phase 2), thus destabilizing the flame and causing local extinction. Methane bubbles move down along the surface and merge into a large methane bubble at the bottom of the sphere. This bubble bursts, releasing methane to form a temporary flame, and the water drops from the hydrate sphere. Water on the surface is cooled by the hydrate inside, and an ice shell confines the methane gas that dissociated inside the sphere. Because the dissociation occurs continuously inside the hydrate, the inner pressure gradually increases and at some instant, the ice cracks and methane gas is ejected from the cracks, which results in a micro-explosion with a flame. In phase 1, the surface temperature is below the freezing point of water, and so the surface remains dry and a stable flame envelope is formed; in phase 2, the surface temperature is above the freezing point, and so water appears on the surface. When the temperature at the center of the sphere is lower (193, 213, or 233 K), some methane hydrate remains even after flame extinction because heat transfer from the flame decreases in phase 2 as a result of local extinction. The diameter of the sphere decreases during combustion in accordance with the d-square law, which indicates that the heat of dissociation is supplied by the flame and methane is supplied by the dissociation of methane hydrate in the sphere, as in single-droplet combustion.

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Simultaneous Measurements of Phosphor Thermometry and PIV for High-temperature Gas Flows

Takeshi Yokomori, Haruko Nagai, Hiroshi Shiratori, Naoki Shino, Naoki Fujisawa, Taro Hirasawa

SAE paper; SAE 2015 Powertrain, Fuels & Lubricants    JSAE20159297/SAE2015-01-2002 2015年09月

研究論文（学術雑誌）, 共著, 査読有り

Flame propagation over a methane hydrate with surface temperature variation in a natural convective flow field

Tomoki Yoshioka, Masanori Suemitsu, Takeshi Yokomori, Ryo Ohmura, Toshihisa Ueda

Bulletin of the JSME, Mechanical Engineering Letters （The Japan Society of Mechanical Engineers）  1   Paper No.15-00370 2015年07月

研究論文（学術雑誌）, 共著, 査読有り

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Experimental and theoretical investigation on hydrogen permeation with flat sheet Pd/Ag membrane for hydrogen mixture with various inlet H-2 mole fractions and species

Hasan Mohd Faizal, Yuki Kawasaki, Takeshi Yokomori, Toshihisa Ueda

Separation and Purification Technology （Elsevier）  149   208 - 215 2015年07月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1383-5866

　概要を見る

The estimation of hydrogen permeation mole flux was performed by previously introduced theoretical equation which considers the decrease in H-2 concentration at the membrane surface, and was compared with experimental result, for various hydrogen mixtures with different inlet H-2 mole fractions and species. A flat sheet 77 wt.% Pd/23 wt.% Ag purification membrane with effective surface area of 3.14 x 10(-4) m(2) was used. For H-2:N-2 mixture, the comparison was performed under various feed flow rates (2.78 x 10(-5)-2.50 x 10(-4) mol/s), for inlet H-2 mole fraction of 0.70-0.80, at reference membrane temperature of 623 K and total upstream pressure of 0.25 MPa. Then, nitrogen was subsequently replaced with argon (Ar), helium (He) and carbon dioxide (CO2) to investigate the applicability of the estimation method for various H-2 mixtures with different species. The results demonstrate that the effect of H-2 permeation itself plays a significant role for permeation with H-2 mixture, which induces the phenomenon of concentration polarization. Overall, the introduced method is able to estimate H-2 permeation mole flux for H2 mixture, both qualitatively and quantitatively, regardless of inlet H-2 mole fraction and species. (C) 2015 Elsevier B.V. All rights reserved.

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Model of Flame Dynamics of Laminar Premixed Flame Subject to the Low Frequency Equivalence Ratio Oscillations

Abdul Rahman Mohd Rosdzimin, Takeshi Yokomori, Toshihisa Ueda

International Communications in Heat and Mass Transfer （PERGAMON-ELSEVIER SCIENCE LTD）  61   8 - 15 2015年02月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0735-1933

　概要を見る

The effect of the non-uniform profile of scalar variables, such a fuel at the upstream and temperature at the downstream of the flame zone was discussed theoretically to elucidate; (1) the deviation of motion from the steady state case and (2) the hysteresis of premixed flames response to the equivalence ratio oscillations seen in an experimental and numerical works. One-dimensional integral model for the non-uniform scalar variable profile with low frequency equivalence ratio oscillation has been developed. Here, the wavelength of the oscillation is assumed to be larger than the nominal flame thickness. Through the integral analysis, we obtained the relation of the flame propagation speed for steady and unsteady cases depending on the non-uniform scalar profile at the upstream and downstream of the flame zone. Hysteresis of the flame propagation speed is found due to the transport of fuel and heat by the non-uniform scalar profile at the upstream and downstream of the flame zone. This result qualitatively agreed with the numerical results of a response of the stagnation laminar CH4/air premixed flames for a low equivalence ratio oscillation frequency. (C) 2014 Elsevier Ltd. All rights reserved.

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Flame Dynamics of Equivalence Ratio Oscillations in a Laminar Stagnating Lean Methane/air Premixed Flame

Hisashi Tomita, Abdul Rahman Mohd Rosdzimin, Sotaro Miyamae, Takeshi Yokomori, Toshihisa Ueda

Proceedings of the Combustion Institute （Elsevier）  35   989 - 997 2015年01月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1540-7489

　概要を見る

This study investigates the effect of fuel concentration oscillation on laminar stagnating premixed flames by both experiment and numerical simulation. The numerical analysis is conducted using ANSYS Fluent 14.5. The equivalence ratio oscillation in the experiments is formed by a novel oscillator with two cylinder piston units that can produce alternating ejections of leaner and richer pre-mixtures. Velocity fluctuation is well suppressed by installing screens on the burner exit. The fuel concentration oscillation between the stagnation plate and the burner exit is visualized and analyzed by acetone ultraviolet light-induced fluorescence in the isothermal condition. The oscillator frequency is varied in the range 2-20 Hz, and the oscillation wavelength is much longer than the flame thickness. The flame oscillates with the fuel concentration, and in the experiment, the amplitude of the flame oscillation attenuates as the frequency of fuel concentration oscillation increases above 5 Hz, which corresponds to a Strouhal number of unity. This indicates that the Strouhal number distinguishes quasi-steadiness for St &lt; 1 and unsteadiness for St &gt; 1. The flame oscillation pattern is a closed loop, which might be attributable to variation of the back support effect on the flame. The numerical results show a similar trend for the flame response to oscillations in fuel concentration. This study finds the flame motion is significantly affected by fuel concentration oscillations, even at low frequencies; in other words, the oscillation wavelength is much longer than the flame thickness, as a result of the back support effect. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

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Numerical investigation of the stagnating laminar premixed methane/air flame with fuel concentration oscillation using a four-step reaction mechanism

Sotaro Miyamae, Abdul Rahman Mohd Rosdzimin, Hisashi Tomita, Takeshi Yokomori, Toshihisa Ueda

Bulletin of the JSME, Mechanical Engineering Journal （The Japan Society of Mechanical Engineers）  1 （ 6 ） Paper No.14-00330 - TEP0060 2014年12月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  2187-9745

　概要を見る

Responses of stagnating laminar methane/air premixed flames under fuel concentration oscillation, i.c., equivalence ratio oscillation, were numerically investigated using a one-step overall reaction mechanism and a four-step reaction mechanism that included CO and H₂ formation. The flame motion was numerically investigated for three different oscillation cases namely: lean, rich and lean-rich crossover case. Methane/air mixtures with sinusoidal equivalence ratio oscillations were issued from the burner exit with uniform 1.0 m/s velocity profiles. In the steady state condition, the one-step overall reaction mechanism and the four-step reaction mechanism had nearly the same characteristics in the lean region, while in the rich region variations in characteristics such as flame location and flame displacement speed for the four-step model were much more significant than those for one-step model. When the equivalence ratio was oscillated, the flame location oscillated. The amplitude of the flame location oscillation did not change with the equivalence ratio oscillation when the frequency of equivalence ratio oscillation was less than 8Hz, while it decreased monotonically when it exceeded 8 Hz. Here 8 Hz corresponds to a Strouhal number (St) of unity. Thus, this result indicates that the flame was in a quasi-steady state when St<1.0 while it became unstable when St>1.0. The variation in flame location and the flame displacement speed did not follow those for the steady state condition and made a limit cycles. This was due to the back support effect. The cycles were significantly inclined at higher frequencies. In the lean condition, the limit cycle was inclined similarly for both the one-step and four-step reaction mechanisms. In the rich condition, however, the limit cycle for the four-step reaction was more inclined than that for the one-step reaction. These results show that the formation of CO and H₂ played an important role in the rich condition.

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Effect of Feed Flow Rate of Hydrogen Mixture on Hydrogen Permeation for Flat Sheet Pd/Ag Membrane with Stagnating Flow

Hasan Mohd Faizal, Ryo Kizu, Takeshi Yokomori, Toshihisa Ueda

Journal of Thermal Science and Technology 8   120-135 2013年04月

研究論文（学術雑誌）, 共著, 査読有り

The Response of a Conical Laminar Premixed Flame to Equivalence Ratio Oscillations in Rich Conditions

Abdul Rahman Mohd Rosdzimin, Takeshi Yokomori, Toshihisa Ueda

Journal of Thermal Science and Technology 8   28-43 2013年02月

研究論文（学術雑誌）, 共著

Y2Si2O7:Eu/SiO2 core shell phosphor particles prepared by flame spray pyrolysis

Hiroshi Hasegawa, Toshihisa Ueda, Takeshi Yokomori

Proceedings of the Combustion Institute （Elsevier）  34   2155-2162 2012年08月

研究論文（学術雑誌）, 共著, 査読有り

Experimental investigation of flame spreading over pure methane hydrate in a laminar boundary layer

Yoshihiro Maruyama, Masaru J. Fuse, Takeshi Yokomori, Ryo Ohmura, Shigeru Watanabe, Toru Iwasaki, Wataru Iwabuchi, Toshihisa Ueda

Proceedings of the Combustion Institute （Elsevier）  34   2131-2138 2012年08月

研究論文（学術雑誌）, 共著

Experimental Study on a Compact Methanol Steam Reformer with Pd/Ag Membrane

Hasan Mohd Faizal, Masato Kuwabara, Ryo Kizu, Takeshi Yokomori, Toshihisa Ueda

Journal of Thermal Science and Technology 7 （ 1 ） 135-150 2012年01月

研究論文（学術雑誌）, 共著, 査読有り

Numerical Investigation of a Flames Response to the Fuel Concentration Oscillation in a Stagnating Laminar Premixed Methane/Air Flames

Abdul Rahman, Mohd Rosdzimin, Takeshi Yokomori, Toshihisa Ueda

Journal of Thermal Science and Technology 7 （ 1 ） 16-30 2012年01月

研究論文（学術雑誌）, 共著, 査読有り

Characteristics of Rare Earth (RE = Eu, Tb, Tm)-doped Y2O3 Phosphors for Thermometry

Naohiro Ishiwada, Toshihisa Ueda, Takeshi Yokomori

Luminescence （Wiley）  26   pp.381-389 2011年12月

研究論文（学術雑誌）, 共著, 査読有り

Co-doped Y2O3:Tb3+/Tm3+ multi-color emitting phosphors for thermometry

Naohiro Ishiwada, Satoko Fujioka, Toshihisa Ueda and Takeshi Yokomori

Optics Letters （Optical Society of America）  36 （ 5 ） 760-762 2011年03月

研究論文（学術雑誌）, 共著, 査読有り

通常スケールの火炎端特性から考察するマイクロフレームの安定性

廣田光智, 横森剛

高温学会誌 36 （ 5 ） pp.217-223 2010年09月

研究論文（学術雑誌）, 共著, 査読有り

Photoluminescence of cubic and monoclinic Gd2O3:Eu phosphors prepared by flame spray pyrolysis

Yasuo Iwako, Yuki Akimoto, Masaki Omiya, Toshihisa Ueda and Takeshi Yokomori

Journal of Luminescence （Elsevier）  130 （ 8 ） 1470-1474 2010年08月

研究論文（学術雑誌）, 共著, 査読有り

Fire Extinction Using Carbon Dioxide Hydrate

Takashi Hatakeyama, Eisuke Aida, Takeshi Yokomori, Ryo Ohmura, Toshihisa Ueda

Industrial & Engineering Chemistry Research （ACS Publications）  48 （ 8 ） 4083-4087 - 4087 2009年03月

研究論文（学術雑誌）, 共著, 査読有り

Combustion Characteristics of Methane Hydrate in a Laminar Boundary Layer

Yuki Nakamura, Ryoji Katsuki, Takeshi Yokomori, Ryo Ohmura, Masahiro Takahashi, Toru Iwasaki, Kazuo Uchida, Toshihisa Ueda

Energy & Fuels （ACS Publications）  23   1145-1449 2009年02月

研究論文（学術雑誌）, 共著, 査読有り

Lower limit of weak flame in a heated channel

Yosuke Tsuboi, Takeshi Yokomori, Kaoru Maruta

Proceedings of the Combustion Institute （Elsevier）  32   3075-3081 2009年

研究論文（学術雑誌）, 共著, 査読有り

Stability of CH4-N2/Air Jet Diffusion Flame for Various Burner Rim Thicknesses

Yasuhiro Otakeyama, Takeshi Yokomori, Masahiko Mizomoto

Proceedings of the Combustion Institute （Elsevier）  32   1091-1097 - 1097 2009年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1540-7489

　概要を見る

The influence of burner rim thickness on the stabilization mechanism of methane diluted with nitrogen and air jet diffusion flame was investigated experimentally. The diffusion flame was stabilized on a two-dimensional Wolfhard-Parker burner with a variable partition wall (burner rim) thickness between the fuel and air jets. The diffusion flame on a thin burner rim showed a blowout at the stability limit, which occurred after the lifted flame behavior. For a thick burner rim, the flame base remained well anchored in the wake region, and a blowoff occurred suddenly and not via the lifted flame with an increase in the jet velocity. For moderate rim thickness, a transition from-a wake-anchored flame to a lifted flame appeared (liftoff), and blowout then occurred as the jet velocity increased. The blowout limits of lifted flames were not influenced by rim thickness; however, the blowoff,limits were extended with an increase in the rim thickness. Particle image velocimetry (PIV) measurements showed that unburned flow entrainment into the base of the lifted flame was of the same order of magnitude as the propagation speed of the premixed flame. Therefore, the stabilization of the lifted diffusion flame for a thin rim might be determined by the premixed propagation of the flame base. On the other hand, a flame base anchored on the thick burner rim experienced a velocity distribution similar to a counterflow. Furthermore, the stretch rates at the liftoff and blowoff limits agreed well with the extinction limits of ordinary counterflow diffusion flames. Thus, their mechanisms could be explained by flame stretched extinction. (c) 2009 The Combustion Institute. Published by Elsevier Inc.-All rights reserved.

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Extinction of Methane/Air Counterflow Partially Premixed Flames

Tomoya Wada, Masahiko Mizomoto, Takeshi Yokomori, Norbert Peters

Proceedings of the Combustion Institute （Elsevier）  32   1075-1082 2009年

研究論文（学術雑誌）, 共著, 査読有り

Extinction Characteristics of Premixed Flame in Heated Microchannel

Yosuke Tsuboi, Takeshi Yokomori, Susumu Hasegawa, Kaoru Maruta

Combustion Science and Technology （Taylor & Francis）  180   2029-2045 2008年11月

研究論文（学術雑誌）, 共著, 査読有り

燃焼によるナノ粒子の合成について -蛍光ナノ粒子の気相燃焼合成法-

横森 剛, 植田 利久, 溝本 雅彦, Yiguang Ju

日本機械学会熱工学部門ニュースレター, TED Plaza （日本機械学会 熱工学部門）  53 2008年02月

研究論文（学術雑誌）, 共著

Electrostatic Probe Measurement in an Industrial Furnace for High-Temperature Air conditions

Takeshi Yokomori, Susumu Mochida, Toshiaki Araake, Kaoru Maruta

Combustion and Flame （Elsevier）  150   369-379 - 379 2007年08月

研究論文（学術雑誌）, 共著, 査読有り

検出電極・補償電極平行ニ極型プローブを利用した静電探針計測による火炎検出

横森 剛, 円山重直, 丸田薫

日本機械学会論文集B編 73 （ 730 ） 1377-1384 2007年06月

研究論文（学術雑誌）, 共著, 査読有り

Flame Synthesis and Characterization of Rare-Earth(Er3+, Ho3+, and Tm3+) doped Upconversion Nanophosphors

Xiao Qin, Takeshi Yokomori, Yiguang Ju

Applied Physics Letters （American Institute of Physics）  90   No.073104 2007年02月

研究論文（学術雑誌）, 共著, 査読有り

Development and scale effects of small Swiss-roll combustors

Nam Il Kim, Satoshi Aizumi, Takeshi Yokomori, Souichiro Kato, Toshiro Fujimori, Kaoru Maruta

Proceedings of the Combustion Institute （Elsevier）  31   3243-3250 2006年08月

研究論文（学術雑誌）, 共著, 査読有り

Flame Behavior in Heated Porous Sand Bed

Seung Gon Kim, Takeshi Yokomori, Nam Il Kim, Sudarshan Kumar, Shigenao Maruyama, Kaoru Maruta

Proceedings of the Combustion Institute （Elsevier）  31   2117-2124 2006年08月

研究論文（学術雑誌）, 共著, 査読有り

Burning Velocity of Triple Flames with Gentle Concentration Gradient

Mitsutomo Hirota, Takeshi Yokomori, Kyouhei Yasuda, Yoshitaka Nagai, Masahiko Mizomoto, Goro Masuya

Proceedings of the Combustion Institute （Elsevier）  31   893-899 2006年08月

研究論文（学術雑誌）, 共著, 査読有り

超過エンタルピ燃焼を用いた小型燃焼加熱器（マイクロコンバスタ）の開発

加藤 壮一郎, 相墨 智, 横森 剛, 丸田 薫

日本燃焼学会誌 48 （ 145 ） 235-240 2006年

研究論文（学術雑誌）, 共著

Stability Limits of Swiss-roll Micro Combustors

Nam Il Kim, Souichiro Kato, Takeshi Yokomori, Takuya Kataoka, Shigenao Maruyama, Toshiro Fujimori, Kaoru Maruta

Thermal Science and Engineering 13 （ 4 ） 7-8 2005年10月

研究論文（学術雑誌）, 共著, 査読有り

Flame Stabilization and Emission of Small Swiss-roll Combustors as Heaters

Nam Il Kim, Souichiro Kato, Takuya Kataoka, Takeshi Yokomori, Shigenao Maruyama, Toshiro Fujimori, Kaoru Maruta

Combustion and Flame （Elsevier）  141   229-240 2005年05月

研究論文（学術雑誌）, 共著, 査読有り

Flame Synthesis of Carbon Nanotubes in a Wall Stagnation Flow

Shunpei Nakazawa, Takeshi Yokomori, Masahiko Mizomoto

Chemical Physics Letters （Elsevier）  403   158-162 2005年02月

研究論文（学術雑誌）, 共著, 査読有り

Flame Temperatures along a Laminar Premixed Flame with a Non-uniform Stretch Rate

Takeshi Yokomori, Masahiko Mizomoto

Combustion and Flame （Elsevier）  135   489-502 2004年12月

研究論文（学術雑誌）, 共著, 査読有り

Emission and Efficiency of Small Swiss-Roll Combustors as Heat Sources

Nam Il Kim, Souichiro Kato, Toshiro Fujimori, Takuya Kataoka, Takeshi Yokomori, Kaoru Maruta, Shigenao Maruyama

Thermal Science and Engineering 12 （ 4 ） 121-122 2004年10月

研究論文（学術雑誌）, 共著, 査読有り

Interaction of Adjacent Flame Surfaces on the Formation of Wrinkling Laminar Premixed Flame

Takeshi Yokomori, Masahiko Mizomoto

Proceedings of The Combustion Institute （Elsevier）  29   1511-1517 2002年08月

研究論文（学術雑誌）, 共著, 査読有り

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しわ状に形成される層流予混合火炎の火炎温度

横森 剛, 溝本 雅彦

日本機械学会論文集（Ｂ編） （Japan Society of Mechanical Engineers）  67 （ 664 ） 3189-3195 - 3195 2001年11月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0387-5016

　概要を見る

The flame temperature of a laminar premixed flame with continuous convex and concave curvatures was experimentally investigated. The flame temperature and the stretch rate along the flame surface were measured for the flame formed in the lean propane/air mixture (φ = 0.72, Lc = 1.74). As a result, the flame temperature at the convex toward the unburned mixture was lower than the adiabatic flame temperature and that of the concave was higher, because of the flame stretch and the Lewis number effect. However, the measured flame temperature was different from the estimated flame temperature by the theory for the local flame structure proposed by C. J. Sun et al. We guess the reason why such difference was arisen is the existence of the heat transfer along the flame surface, so we suggest that the heat transfer along the flame surface should be considered in the case of the flame with continuous convex and concave curvatures.

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