Effect of Rich and High Turbulence Combustion on Emissions and Flame Behavior in a Direct--Injection Diesel Engine

摘要

This study tried to reduce NO. and particulate emissions simutaneously in a high speed direct- injection diesel engine. Fuel--rich combustion was used to reduce NO. emission at initial combustion stage and high turbulence combustion was used to reduce particulate emission at diffusion combus- tion stage. Experiments were carried out to investigate the effects of high squish combustion chambers with small throat on combustion process and exhaust emissions. Results showed that in the high squish combustion chamber, both NO. and particulate emissions reduced with retarded injection timing. Endoscopic high speed photography was employed to analyze experimental results. In the original combustion chamber at the early combustion stage, the high luminosity flame tended to spread out of the cavity. Fuel-rich mixture burned slowly over the piston crown. In the high squish combustion chamber, flame rotated violently around the bowl. Fuel--rich mixture was kept beneath the squish lip, and was mainly oxidized inside the bowl. This combustion phenomenon was consid- ered to be one of the reasons for low particulate emission in high squish combustion chambers.