Abstract:

The reentrant combustion chamber shape of a high-speed direct-injection vehicle diesel engine was improved to form required airflow-characteristics in the chamber. The dynamics of incylinder flow field, the airfuel ratio distribution, and the temperature field were simulated by commercial CFD software FIRE for the airflow matching the fuel spray characteristics by different injection pressures. The air-fuel mixture formation of the diesel engine was studied by simulation, and the effects of the obtained mixture formation behavior on the combustion and exhaust emissions were investigated experimentally. The results showed that the ignition delay, the premixed combustion proportion and the diffusion combustion process can be controlled by optimal matching between the airflow characteristics in the reentrant combustion chamber and the fuel injection pressure, thus to control the high temperature combustion duration. The optimization can effectively reduce the NOx and soot emissions simultanceously withoult penalty on fuel economy.

Key words: power machinery and engineering, direct-injection diesel engine, combustion chamber, airflow characteristic, injection pressure, matching, combustion process, exhaust emission