Lean combustion has the advantage of low pollutant emission levels, but its combustion rate is very low and the lean mixtures are difficult to ignite and form stable flames. To improve these disadvantages, we have focused on hydrogen addition to a premixed mixture. In this study, we have experimentally observed the characteristics of tubular flames for methane/air mixtures with hydrogen, and have investigated the effects of hydrogen addition on lean combustion in a swirling flow. We have measured the flame diameter, flame temperature and extinction limit, and tried to obtain the burning velocity. We have discussed the flame characteristics and transport process based on the flame and flow configurations. Results show that, as the concentration of added hydrogen is increased, (1) the flame diameter monotonically increases, (2) the fuel concentration at the extinction linearly decreases and effective equivalence ratio also decreases, (3) the radial temperature distribution becomes an M-shaped profile and the flame temperature increases, and (4) the burning velocity increases. As the rotational intensity is increased, these phenomena are more prominent. In a swirling flow, the pressure decreases around the rotational axis due to the centrifugal effects. The pressure gradient is formed, and there is mass transport due to pressure gradient (pressure diffusion), which changes kinetic process in flames. The reaction rate is changed through these phenomena, and the rotational effects appear. The present results provide the basic, useful information on practically important lean combustion.

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An effective fuel injection for reducing harmful substances such as hydrocarbon (HC) and carbon monoxide (CO) of vehicle exhaust gas is researched in this study. Reductions of fuel injection quantity during engine cold condition is very effective, because major portion of HC and CO, both unburned harmful substances, are emitted in the phase. The fuel reduction control, based on sliding mode control theory, uses feedback from measured Air/Fuel ratio by linear A/F sensor to avoid engine torque fluctuation. It is confirmed that the fuel control is very effective to reduce exhaust emissions by simulations and experimental results.

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In a pentroof type combustion chamber of spark-ignition engine, a tumbling flow is broken down to small scale eddies near the top dead center in compression stroke and promotes the flame propagation. The effects of tumbling flow and its turbulence on combustion were investigated by analyzing combustion pressure and ion-current wave form. The number of peaks of ion current wave N^^-_p increases with the increase in turbulence intensity. The mean rate of heat release in the early stage of combustion increases linearly with the increase of N^^-_p. The spacing of flamelet surfaces in burning zone of turbulent flame decreases with the increase in turbulence intensity.

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The paper discusses the methodology of predicting combustion and NO formation in large scale diesel engines from scale model experiments, and shows the results of experiments conducted to validate the scale model theory. Combustion similarity means that flow patterns and flame distribution develop similarly in differently sized engines, so allowing heat release rates and thermal efficiency to be predicted from scale model experiments. Based on an analysis of NO formation, an algorithm to predict emissions is also established. An experiment was performed to compare predictions based on scale model experiments and experimental results with two sets of similar engines ranging from 85 to 125 and from 600 to 800 mm bore. The results showed good agreement with the theoretical predictions, indicating possibility of the scale model experiment for diesel engine combustion.

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Three dimensional computations were carried out to study the effects of engine operating conditions on NO_x emissions from premixed lean diesel combustion in a DI engine. A modified KIVA II computer code was used to the numerical simulation. Qualitatively good agreement between computational and experimental results for impinging fuel spray shape, heat release rate and relative NO_x mass has been achieved. The computational results demonstrate that NO_x emissions are significantly influenced by temperature of intake air, fuel injection timing, and fuel ignitability. It is also indicated that fuel droplets gathered into the squish region are possible to become unburned fuel emissions.

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In order to investigate the optimization of several parameters to control fuel injection rate on in line pump based fuel injection system for DI diesel engines, a computer model simulating the flow in fuel injection system was developed including a cavitation model for nozzle holes. For the validation of this model, comparison with experimental data was performed for a wide range of pump operating conditions. Following that successful validation of this model, parameteic studies were performed which could allow improved fuel injection system design.

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In this study, a new submodel concerning fuel film formation process is proposed order to simulate the behavior of diesel spray impingement on wall surface. Here, super-heating degree of the surface, defined by the temperature difference between the wall surface and the fuel saturated temperature, is newly considered for behavior of impinged liquid droplets. In this spray impingement submodel, fuel film formation process, droplet interaction film breakup process, and velocity and direction of dispersing droplets were considered based on several experimental results. This new submodel was incorporated into KIVA-II code. As a results, it is found that the calculated results of impinging spray behavior by the new model agree well with experimental results.

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In the case of gasoline engines, the fuel injected into the intake port adheres surely on its wall and the inlet valve, consequently, the wall impinging spray interaction should occur the generation of unburned hydrocarbons and uncontrol-lable mixture formation. Therefore, it is very important to analyze the fuel behavior during the spray-wall interaction. In this study, the submodel concerning the spray impingement is constructed in order to simulate the fuel behavior for gasoline spray inside intake manifold. In this submodel, fuel film formation process, film transportation process, droplet interaction film breakup process, and velocity and direction of dispersing droplets were considered based on several experimental results and was incorporated into KIVA-II code. As a results, it was possible to calculate results of impinging spray behavior.

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This paper describes new design methods of micro Stirling engines. By designing the phase angle of two engines at 90 degrees instead of 180 degrees, the engine, which we named TF 4 (Torque Flatting 4 cylinder) engine, generates continuous positive and smooth torque, so it does not need a flywheel to supplement negative torque. Although raising buffer pressure is effective to improve power of Stirling engine, it is difficult to apply mechanical seals for micro Stirling engines. Instead of mechanical seal, we suggest magnetic clutches that transmit engine torque noncontactly. Using magnetic clutches, it is possible to avoid rotary seal parts and decrease friction loss. Based on the proposed methods, we manufactured high specific power miniaturizing alpha type Stirling engines of 0.074 cc swept volume whose maximum frequency is 317 Hz. We also prove the performance of the engines and magnetic clutches.

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