Effect of internal exhaust gas recirculation on the combustion characteristics of gasoline compression ignition engine under low to idle conditions

Internal exhaust gas recirculation (iEGR) is one of the effective methods to improve combustion stability of gasoline compression ignition (GCI) engine under low load conditions. However, the heating effect to the ambient gas, the dilution effect to O2 concentration, and the changing of heat capacity, which are caused by introducing iEGR into cylinder, have complicated influences on combustion process. The present work comprehensively investigates the competitive relationship between heating effect and dilution & heat capacity effect on combustion characteristics in GCI engine under different engine loads. Under low load conditions, there is a competitive relationship between heating effect and dilute & heat capacity effect of iEGR on start of combustion (SoC) and burning rate. The burning rate firstly rises and then decreases as iEGR ratio increases from low to high due to the competitive relationship. However, the SoC is controlled by both fuel distribution and the competitive relationship. In addition, under idle conditions, the heating effect plays the dominant role in combustion process and improves the combustion stability. In this way, the low load limit has been successfully extended by using high iEGR ratio. Meanwhile, the idling fuel consumption per unit displacement reaches the same level of commercial vehicles'.