Tomidokoro, Takuya

写真a

Affiliation

Faculty of Science and Technology, Department of Mechanical Engineering (Yagami)

Position

Assistant Professor (Non-tenured)/Research Associate (Non-tenured)/Instructor (Non-tenured)

External Links

Academic Background 【 Display / hide

  • 2019.04
    -
    2022.03

    Keio University, School of Science and Technology, School of Science for Open and Environmental Systems

    Graduate School, Completed, Doctoral course

Academic Degrees 【 Display / hide

  • Ph.D. (Engineering), Keio University, Coursework, 2022.03

 

Papers 【 Display / hide

  • 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 2022.07

    ISSN  00102180

     View Summary

    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.

  • 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 )  2022.02

    ISSN  19463936

     View Summary

    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.

  • 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 2021.01

    ISSN  15407489

     View Summary

    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.

  • Characteristics of counterflow premixed flames with low frequency composition fluctuations

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

    Combustion and Flame (Combustion and Flame)  212   13 - 24 2020.02

    ISSN  00102180

     View Summary

    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.

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

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

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

     View Summary

    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.

 

Courses Taught 【 Display / hide

  • LABORATORY IN SCIENCE

    2022

  • LABORATORIES IN SCIENCE AND TECHNOLOGY

    2022

  • EXPRESSION OF MECHANICAL PRODUCTS

    2022

  • LABORATORY IN SCIENCE

    2021

  • LABORATORIES IN SCIENCE AND TECHNOLOGY

    2021

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