Comparative analysis on combustion and emissions between CO2 and EGR dilution GDI engine at half-load, stoichiometric and lean-burn conditions

In this paper, CO2 or EGR (exhaust gas recirculation) as dilution gas was introduced into the intake system. The impacts of CO2 or EGR dilution on combustion and emissions of a GDI (gasoline direct injection) engine at halfload, stoichiometric and lean-burn conditions were investigated experimental by comparison. The study findings show that the deterioration combustion of CO2 dilution was weaker than that of EGR dilution. Dilution rate of CO2 dilution for the same combustion process was about 2 times of EGR dilution. At 20% dilution rate, the combustion center for CO2 dilution was roughly 25.2% and 13.9% earlier than that of EGR dilution at stoichiometric and lean-burn mixture, severally; the CO and HC emissions for CO2 dilution were roughly 43.7% and 28.6% lower than those of EGR dilution at stoichiometric mixture, severally; and the NOX emissions for EGR dilution were around 74.8% and 58.7% lower than those of CO2 dilution at stoichiometric and lean-burn mixture, severally; and the soot emission of CO2 dilution was roughly 26.5% higher than that of EGR dilution at stoichiometric mixture, and the soot emission of CO2 dilution was roughly 33.9% lower than that of EGR dilution at lean-burn mixture. In terms of engineering applications, the CO2 dilution had more advantageous compared with EGR dilution in a GDI engine. But for obtaining the same combustion, the dilution rate for CO2 dilution should be significantly increased than that of EGR dilution.