Faculty Profiles - YAMAMOTO, Kazuhiro

Papers - YAMAMOTO, Kazuhiro

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Numerical Study on Ignition Characteristics of Methane-air Mixture Using Detailed Chemical Kinetics (Effect of Equivalence Ratio and Heat Loss to Electrode on Ignition Characteristics), Reviewed

J. Han, H. Yamashita, and K. Yamamoto

Proc. 6th Int. Conf. Computational Heat and Mass Transfer page： 165-170 2009.5

Language：English Publishing type：Research paper (scientific journal)

Ignition is a transient combustion phenomenon and one of the most difficult and complex problems, which includes a lot of physical and chemical processes, so that it has not yet been explained sufficiently. In the present study, the ignition characteristics of methane-air mixture were investigated by numerical analysis using detailed chemical kinetics. Minimum Ignition Energy (MIE) is an important parameter of ignition ability of the system. In order to investigate the effect of the equivalence ratio, electrode gap and size on MIE in the quiescent methane/air mixture, ignition processes were examined considering the heat loss to electrode for axisymmetric numerical model, in which the temperatures of electrode wall were set at 300K, 1000K and 2000K. The GRI-mech 3.0 consisting of 53 species and 325 elementary reactions was applied to the chemical kinetics model. The obtained calculation results were compared with experimental results. The results with heat loss to electrode of wall temperature 300K showed good agreement with experimental results for the relationships of MIE to the equivalence ratio and electrode gap.

After-treatmentof Diesel Particles by Diesel Exhaust Gas Perfect Burning System Reviewed

K. Yamamoto, K. Matsui, M. Nakamura, and H. Yamashita

Proc. 6th Int. Conf. Computational Heat and Mass Transfer page： 361-366 2009.5

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Diesel engines have been used in a wide variety of commercial vehicles. Since the pollution emitted by diesel cars causes environmental problems, stricter diesel emissions standards are being set in many counties. To meet future PM emission standards, we have focused on diesel exhaust gas perfect burning system (DEGPBS), which is the after-treatment of exhaust gas developed by COTEC Company, Ltd. in Japan. So far, it is difficult to observe the phenomena in the filter experimentally, and there is not enough information on the particle combustion in the filter regeneration process. In this study, we conducted simulation of soot combustion by the lattice Boltzmann method. The inner structure of the filter was obtained by a 3D X-ray CT technique. Results show that the combustion reaction is well simulated to discuss the soot oxidation inside the filter.

DPF内のすす堆積を考慮した流れの数値解析 Reviewed

大堀晋也，山本和弘，山下博史，大道重樹

日本機械学会論文集（B編） Vol. 75 ( 750 ) page： 370-377 2009.2

*Burning Velocity and OH Concentration in Premixed Combustion Reviewed

K. Yamamoto, M. Ozeki, N. Hayashi, H. Yamashita

Proceedings of the Combustion Institute Vol. 32 page： 1227-1235 2009.1

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

In the present paper, we have simulated laminar premixed flames in several types of flow configuration. The counter-flow flame, 1D flame in uniform flow, and 2D flame on a slot burner have been considered. The fuel is propane, and detailed chemistry has been used. We have obtained burning velocity in these flames to examine the response of peak OH concentration in flame zone to burning velocity (SL). In case of counter-flow flame, peak OH concentration is decreased at the larger stretch rate. At the same time, the burning velocity is decreased. The peak OH concentration of 1D flame in uniform flow is decreased at lower equivalence ratio, with smaller burning velocity. It is interesting to note that, for both flames as well as 2D flame, the same linear relationship is observed between two parameters of peak OH and SL . Thus, consistent with earlier findings of turbulent flames, peak OH concentration can be a good measure of burning velocity. In the experiments, we have estimated local burning velocity in turbulent combustion with a cyclone-jet combustor. The slot burner has been used for calibration. It is found that the peak OH concentration in the flame becomes smaller with an increase of turbulence. The local burning velocity is monotonically decreased at higher turbulence. In some cases, its value is almost zero, which could be local extinction. When the fuel is propane, Markstein number is positive for lean mixture. In that case, the burning velocity is decreased due to the stretch effect, which is well in accordance with the fact that the turbulence always suppresses the burning velocity in our measurements.

Microstructure and Particle-laden Flow in Diesel Particulate Filter Reviewed

K. Yamamoto, S. Satake, H. Yamashita

Int. J. Thermal Sciences Vol. 48 page： 303-307 2009.1

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Due to the public awareness with regard to harmful diesel emissions, more strict diesel emissions standards such as Euro V in 2008 are being set in the world. As one of the key technologies, a diesel particulate filter (DPF) has been developed to reduce particulate matters (PM) in the after-treatment of exhaust gas. Since the structure of the filter is small and complex, it is impossible to examine the phenomena inside the filter experimentally. In this study, we conducted fluid simulation in DPF. We used the lattice Boltzmann method (LBM). The microstructure of DPF was taken into account. The complex flow pattern appears by using the non-slip boundary condition on the filter wall surface. The soot accumulation was simulated to consider the PM trap in the diesel filter. Results show that the flow is largely changed due to soot deposition. As the soot concentration inside the filter is increased, the filter backpressure is increased.

*Fluid Simulation and X-ray CT Images for Soot Deposition in a Diesel Filter Reviewed

K. Yamamoto, S. Satake, H. Yamashita, N. Takada, M. Misawa

European Physical Journal Vol. 171 page： 205-212 2009.1

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Recently, more strict diesel particulate emissions standards have been set in many countries. As for the after-treatment of exhaust gas, a diesel filter has been developed to trap diesel particles with small-scale porous structure. Since measurement of flow inside the filter is impossible, the phenomena of particle deposition in the filter are not well understood. In this study, we conducted Lattice Boltzmann simulation on flow in the newly developed diesel filter. The soot deposition was included to consider the particle trap inside the filter. The inner structure of the diesel filter as well as trapped soot region was scanned by a X-ray CT technique. Results show that the flow pattern is largely changed when the soot is attached to the filter surface. By comparing simulation results with CT images, soot accumulation region is well predicted. The amount of trapped soot is proportional to the filter back-pressure.

*Simulation on Soot Deposition and Combustion in Diesel Particulate Filter Reviewed

K. Yamamoto, S. Oohori, H. Yamashita, S. Daido

Proceedings of the Combustion Institute Vol. 32 page： 1965-1972 2009.1

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

We have simulated the flow in a real cordierite DPF using the lattice Boltzmann method. Inner structure of the filter is analyzed by a 3D X-ray CT technique. Two processes of soot deposition for PM trap and soot combustion for filter regeneration process are considered. Especially, the effect of NO2 on the soot oxidation is examined, which is recently proposed as on-board regeneration system. The reaction rate has been determined based on previous experimental data. Results show that, the flow field and pressure change inside the filter are clearly visualized. The pressure distribution depends on the non-uniformity of pore structure. The flow is largely changed with soot deposition, with higher pressure drop across the filter (filter back-pressure). The obtained correlation between total accumulated soot and the filter back-pressure is well in accordance with reported experimental results. In combustion simulation, the effect of NO2 addition to promote the soot oxidation is confirmed. These are useful information to develop the future regenerating DPF system.

三重管バーナの燃焼特性と火炎構造の検討 Reviewed

大島久治，山本和弘，林直樹，山下博史，奥山悟郎

日本機械学会論文集（B編） Vol. 74 ( 748 ) page： 2731-2737 2008.12

Simulation on Flow and Heat Transfer in Diesel Particulate Filter Reviewed

K. Yamamoto, M. Nakamura, and H. Yamashita

Proc. 2nd Thermal Issues in Emerging Technologies page： 245-250 2008.12

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

In this study, we simulate the flow in DPF by the lattice Boltzmann method (LBM). So far, the LBM has been widely used in fluid simulation, and has been an alternative and promising numerical scheme. It has been confirmed that, through the Chapman-Enskog procedure, the Navier-Stokes equations are derived from LB equations. In the LBM, the treatment of boundary conditions is simple and easy, and it is appropriate to simulate porous media flows such as DPF. In this paper, our approach for LB simulation of combustion is briefly explained. Here, the real filter is used in the simulation. The inner structure of the filter sample is scanned by a 3D X-ray CT technique. By conducting tomography-assisted simulation, we obtain local velocity and pressure distributions in the filter, which is hardly obtained by measurements. First, the flow and pressure profiles are visualized, compared with the empirical equation of the Ergun equation. Then, the soot combustion is simulated. Based on the temperature change and reaction inside the filter, the heat and mass transfer in the filter regeneration process is discussed.

セルラオートマトンによる火災時の避難行動のシミュレーション Reviewed

小久保聡，山本和弘，山下博史

日本機械学会論文集（B編） Vol. 74 ( 748 ) page： 2724-2730 2008.12

実数型セルオートマトン法による火災時の避難シミュレーション Reviewed

山本和弘，小久保聡，山下博史

第14回交通流のシミュレーションシンポジウム論文集 page： 9-12 2008.11

ランキン渦中での予混合火炎伝播に与える渦核半径の影響に関する数値解析 Reviewed

近藤周司，山下博史，篠田昌久，山本和弘

日本機械学会論文集（B編） Vol. 74 ( 747 ) page： 2387-2392 2008.11

非定常対向流予混合火炎の火炎構造に与える流入速度変動の影響に関する数値解析 Reviewed

野々村一樹，山下博史，林直樹，山本和弘

日本機械学会論文集（B編） Vol. 74 ( 747 ) page： 2393-2400 2008.11

Simulation of Fire Evacuation by Real-Coded Cellular Automata (RCA) Reviewed

K. Yamamoto, S. Kokubo, H. Yamashita, K. Nishinari

Lecture Notes in Computer Science Vol. 5191 page： 447-454 2008.9

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

We present simulation of fire evacuation by real-coded Cellular Automata (RCA), which is a new approach for pedestrian dynamics. Here, we consider the evacuation from a relatively large room with one or two exits. To describe the flame spread in fire, a percolation model is applied, where the flame position is determined stochastically. In the simulation, we focus on several parameters including the number of people in room, the route keeping away from the flame, and the location of the exit.

Evacuation Simulation in Fire by Real-Coded Cellular Automata Reviewed

K. Yamamoto, S. Kokubo, H. Yamashita

Proceedings of CSI SymposiumInstitute page： in press 2008.9

Authorship：Lead author Language：English

Fire is one of the most serious disasters. The damage in fire is mainly caused by high heat fluxes from the flame, accidental explosions, and toxic species in smoke generated by combustion reaction, which causes fatalities, destruction of houses and buildings, and air pollution. In order to mitigate these losses, it is important to design the room size and exit location in the building for the fire evacuation to set the evacuation route and provide effective instruments including fire extinguishers and alarms. Additionally, an appropriate management for safety such as dairy training for fire evacuation is needed. In planning individual actions for safety and evaluating the effectiveness of facilities and instruments, it is plausible to understand the phenomena in fire and validate the fire evacuation plan in advance. However, it is difficult to conduct experiments inside the building in fire, because the costs are expectedly huge, and the people are exposed to danger. Therefore, the simulation of fire evacuation is needed. For this purpose, we need to describe the evacuee's behaviors in fire. Since its dynamics is caused by collective crowd behavior, we have difficulties to handle directly each motion by solving coupled differential equations. In this study, we present simulation of fire evacuation by real-coded Cellular Automata (RCA), which is our new approach for pedestrian dynamics. Here, we consider the evacuation from a relatively large room with one or two exits. To describe the flame spread in fire, a percolation model is applied, where the flame position is determined stochastically. In the simulation, we focus on several parameters including the number of people in room, the distance of evacuation route from the flame, and the location of the exit.

Evacuation Simulation in Floor Field by Real-Coded Cellular Automata Reviewed

K. Yamamoto

Lecture Notes in Computer Science Vol. 5191 page： 571-574 2008.9

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

This paper presented the simulation of room evacuation by the real-coded cellular automata (RCA). The motion of each evacuee was determined by the floor. Only static floor field was used, corresponding to the shortest distance to the exit. We considered two cases with and without obstacle. We changed the initial number of people in the room and the exit width. We concluded that RCA can be a good tool to discuss the total evacuation time and the evacuation route.

Flame Spread over a Solid Fuel and Lewis Number Effect in Partially Premixed Atmospheres Reviewed

K. Yamamoto, Yoshinori Ogata, H. Yamashita

32nd International Symposium on Combustion page： 68 2008.8

Authorship：Lead author Language：English

We have investigated the downward flame spread over a thin solid fuel. Hydrogen, methane, and propane, included in the gaseous product of pyrolysis reaction, are added in the ambient air. The fuel concentration is kept below the lean flammability limit to observe the partially premixing effect. Both experimental and numerical studies have been conducted. Results show that, in the partially premixed atmospheres, the flame region is expanded vertically and horizontally, and the flame spread rate is increased. It is interesting to note that, based on the flame index, the premixed flame is formed next to the original diffusion flame. Here, we focus on the heat input by adding the fuel in the opposed air, which could be the direct effect to intensify the reaction in the flame region. The dependence of the flame spread rate on the heat input is almost the same for methane and propane/air mixtures, but larger effect is observed for hydrogen/air mixture. Since the deficient reactant in lean mixture is fuel, the larger effect of hydrogen could be explained based on the Lewis number consideration. That is, the combustion is surely intensified for all cases, but this effect is larger for lean hydrogen/air mixture (Le < 1), because more fuel diffuses toward the flame zone to increase the reaction rate. It is concluded that due to the heat input of the added fuel in partially premixed mixture, the larger heat transfer to the unburned region occurs, resulting in an increase of the flame spread rate.

Local Flame Structure and Turbulent Burning Velocity by OH-HCHO PLIF Technique Reviewed

K. Yamamoto, M. Ohnishi, S. Ishii, N. Hayashi, H. Yamashita

32nd International Symposium on Combustion page： 86 2008.8

Authorship：Lead author Language：English

In this study, we have examined local flame structure and heat release rate by simultaneous OH-HCHO PLIF technique. We have used a cyclone-jet combustor to establish turbulent premixed flames for propane/air mixtures in a wide range of turbulence, covering the flamelet regime and thin reaction zones regime on combustion diagram. Results show that as the mean velocity at the combustor exit is increased, more complex flame structure is observed with multiple flamelets. Near the global extinction, peak OH concentration in reaction zone becomes almost zero, whereas HCHO concentration in preheat zone still remains. As a result, the large reduction of heat release rate occurs, resulting in local extinction. The turbulent burning velocity determined by the mean flame shape is increased with turbulence, and the bending effect is observed in thin reaction zones regime. On the other hand, the flame surface area is monotonically increased. The estimated local burning velocity based on peak OH concentration is decreased. Thus, in thin reaction zones regime, the alteration of the flame structure appears with overall reduction of combustion rate. This bending effect can be explained with a decrease of local burning velocity, which is unrecoverable from the increase of flame surface area.

超小型燃焼器の開発に関する詳細素反応機構を考慮した数値解析 Reviewed

鈴木新，山下博史，山本和弘

日本機械学会論文集（B編） Vol. 74 ( 743 ) page： 1641-1648 2008.7

メタルハニカム内のディーゼル微粒子燃焼シミュレーション Reviewed

山本和弘

日本機械学会論文集（B編） Vol. 74 ( 742 ) page： 1318-1823 2008.6

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Papers - YAMAMOTO, Kazuhiro