窪山 達也

Recent progress in the enhanced ignition system, including the conventional spark ignition system, was introduced in this report. At first, the spark discharge channel behavior and its effect on the ignition of lean or diluted mixture was discussed. Next, as novel ignition technologies, the low-temperature plasma ignition system and the pre-chamber ignition system were introduced, and the performance of those systems were discussed.

The objective of this research is to investigate the effect of the EGR guide employed to generate a strong in-cylinder thermal stratification on the recharged EGR gas flow into the cylinder in a gasoline HCCI engine equipped with the blowdown supercharging (BDSC) system. The recharged EGR gas flow was visualized using an optical access engine by motoring. Gas flow from the exhaust port into the cylinder was visualized via PIV method. The results indicate that the flow field pattern is largely affected by the EGR guide's height, and that an increase in the EGR guide's height is effective to generate a strong in-cylinder thermal stratification.

The objective of this study is to establish a control strategy for a HCCI engine equipped with the blowdown supercharging system during the operating mode switching between HCCI and SI. 1-D numerical simulation model was developed to investigate transient behaviors of air-fuel mass ratio and gas-fuel mass ratio during the combustion mode transition. Using this code, an appropriate method to realize a smooth mode transition was explored. The simulation result indicates that a smooth operating mode transition would be possible with the optimized operating timings of the actuators such as intake throttle, exhaust throttle and fuel injector.

The objective of this research is to investigate the effect of the EGR guide employed to generate a strong in-cylinder thermal stratification on the recharged EGR gas flow into the cylinder in the gasoline HCCI engine equipped with the blowdown supercharging (BDSC) system. The recharged EGR gas flow was visualized using an optical access engine. A steady gas flow from the exhaust port into the cylinder was visualized via PIV method. The effect of the pressure difference between the exhaust port and the cylinder and the geometry of the EGR guide on the recharged gas flow were investigated. The results indicate that the flow field pattern is largely affected by the EGR guide height, and that an increase in the EGR guide height is effective to generate a strong in-cylinder thermal stratification.

The objective of this study is to investigate the relationship among heat loss through the chamber wall of diesel engines and the spray flame impingement on the wall, the flame motion and the combustion characteristics such as flame temperature and rate of heat release. Local heat flux at 6 locations on the piston head of a rapid compression and expansion machine, by which experimental conditions such as injection conditions, ambient conditions, can be independently controlled, were measured by thin film thermocouples. The spray flame in an optically accessible combustion chamber with a quartz piston head was imaged by a digital high speed camera to observe the flame motion. From the high speed direct photographs, flame temperature distribution was obtained via two-color method. These measurements were conducted with changing the nozzle orifice diameter of fuel injector and the swirl ratio to investigate the effects of relative flame motion to the chamber wall on the heat loss. The ambient oxygen concentration was also changed as parameter to investigate the effects of combustion characteristics including flame temperature, ignition delay, combustion duration, and rate of heat release, which are affected significantly by oxygen concentration, on the heat flux on the chamber wall. Experimental results showed that the magnitude of heat flux is determined mainly by flame temperature and the relative distribution of heat flux is determined by the distribution of high temperature region in the flame. However, at flame impinging region on the wall, flow motion induced by the spray contributes to increase in heat flux. As nozzle orifice diameter is decreased, average flame temperature is increased, however, local heat flux at the bottom of the piston cavity decreases due to decrease in spray flame penetration. As ambient oxygen concentration is decreased, average flame temperature decreases, and this results in the decrease in local heat flux in the piston cavity. On the other hand, the relative distribution of heat flux is not affected by ambient oxygen concentration. The distribution of heat flux on the piston cavity wall is strongly affected by the swirl motion because the relative flame location to the chamber wall is changed significantly by the change in swirl ratio.