This study investigates the fuel reactivity and the fuel injection strategy effects on gasoline compression ignition (GCI) using the third generation (Gen3) of the gasoline direct injection compression ignition (GDCI) engine with a 14.3 compression ratio (CR). By varying the fuel injection strategy, three GCI combustion modes were studied, including early partially premixed compression ignition (PPCI), late PPCI, and PPCI-diffusion. A double injection strategy was used in all three combustion modes. For early and late PPCI, the first injection took place in the intake stroke, while the onset of the second injection event was varied in the compression stroke. In contrast, in the PPCI-diffusion mode, both injections occurred in the compression stroke with the second injection event taking place near the compression top dead center (TDC).
The investigation was focused at 1500 rpm/6 bar IMEPg. First, the fuel reactivity effects were evaluated on two gasolines with research octane numbers (RON) of 80 and 92. Then, using the RON92 gasoline, the fuel injection strategy effects were investigated. Compared to the RON80 gasoline, the RON92 gasoline was found to require a higher boost to achieve proper PPCI combustion and generate markedly higher combustion losses, thereby causing deteriorated fuel efficiency. In terms of the fuel injection strategy effects, early PPCI produced high fuel efficiency with low nitrogen oxides (NOx) and soot emissions, but it was at the cost of high hydrocarbon (HC) and carbon monoxide (CO) emissions. In contrast, PPCI-diffusion generated drastically reduced combustion losses than both early and late PPCI. Closed-cycle three-dimensional (3-D) combustion computational fluid dynamics (CFD) analysis revealed that PPCI-diffusion had the strongest in-cylinder fuel stratification among the three combustion modes with the main combustion event proceeding through a diffusion-driven process.
