Effect of injection timing retard on ISI strategy in lean-burning LPG direct injection engines

Because of the concerns regarding global warming caused by greenhouse gases and the high cost of fossil fuels, research on improving the fuel economy and emissions in internal combustion engines has become important. Specifically for spark ignition engines, lean-burning direct injection is the most promising technology because the fuel economy and emissions can be improved using a stable combustion of a stratified mixture. This study aimed to develop a spray-guided, lean-burning liquefied petroleum gas (LPG) direct injection engine through optimizing the combustion parameter controls. In previous research, the brake thermal efficiency in an LPG direct injection engine was significantly increased and stable combustion was secured with an interinjection spark ignition (ISI) strategy under low-load operating conditions. However, the simple application of an ISI strategy does not improve the combustion stability under relatively high-load operating conditions, and consequently, the extent of specific fuel consumption reduction is small. In the present study, the effect of injection timing on the combustion stability was assessed and the fuel economy and emission characteristics were compared. Retarding the 2^nd injection timing of the ISI strategy effectively improved combustion stability, but it did not reduce the fuel consumption.