Experimental Investigation on the Effects of Injection Strategy on Combustion and Emission in a Heavy-Duty Diesel Engine Fueled with Gasoline

Gasoline partially premixed combustion shows the potential to achieve clean and high-efficiency combustion. Injection strategies show great influence on in-cylinder air flow and in-cylinder fuel distribution before auto-ignition, which can significantly affect the combustion characteristics and emissions. This study explored the effects of various injection strategies, including port fuel injection (PFI), single direct injection (DI_m), double direct injection (DI_p+DI_m) and port fuel injection coupled with a direct injection (PFI+DI_m) on the combustion characteristics and emissions in a modified single cylinder heavy-duty diesel engine fueled with 92# gasoline at low load. The investigation consists of two parts. Firstly, the comparison among PFI, PFI+DI_m, and DI_p+DI_m strategies was conducted at a fixed CA50 to explore the effects of PFI+DI_m and DI_p+DI_m strategies on the thermal efficiency and combustion stability. The results show that the coefficient of variation (COV) of indicated mean effective pressure (IMEP) with PFI+DI_m and DI_p+DI_m strategies is lower than that of PFI strategy. High thermal efficiency can be achieved while still maintaining low NO_x and soot emissions by using PFI+DI_m strategy. Injection timings of DI_m and DI_p have strong effects on concentration stratification. Next, in order to explore the behavior of PFI+DI_m and DI_p+DI_m strategies in improving the controllability of auto-ignition and combustion phasing, DI_m timings of PFI+DI_m, DI_p+DI_m and DI_m strategies were swept from 9 to MAX°CA BTDC (limited by peak pressure rise rate and in-cylinder pressure). The results show that PFI+DI_m and DI_p+DI_m strategies have significant advantages in controlling CA5 and CA50 over a wide stable operation range.