Influences of pilot injection and exhaust gas recirculation (EGR) on combustion and emissions in a HCCI-DI combustion engine

Abstract

The HCCI-DI combustion mode was achieved in a heavy-duty diesel engine using the early pilot injection in the intake stroke and the main injection around compression top dead center (TDC). The effects of pilot injection quantity and EGR rate on HCCI-DI combustion and emissions were investigated. NOx emission has a dramatically decrease as the pilot injection quantity increases, but it is still in a high level that needs to be reduced. The smoke emission has a slight increase with the rise of pilot quantity, but it is always in a low level. The increasing HC and CO emissions can be easily removed by the diesel oxidation catalyst (DOC). The HCCI-DI combustion with low level of EGR is an effective method to reduce NOx emission further, and smoke emission increases as EGR rate increases, but it is in an acceptable level. The HCCI-DI combustion mode operating range is limited by the peak of cylinder pressure, the pressure rise rate and the cycle-to-cycle variations. There are optimal EGR rates and pilot quantities to achieve low NOx and low smoke emissions.