Combined effects of fuel reactivity and intake thermodynamic conditions on heat release and emissions of compression ignition combustion

A numerical simulation is performed to study the effects of fuel reactivity and intake thermodynamic conditions on combustion and emission characteristics of compression ignition combustion and the cooperative optimization strategies. Three fuels with representative octane number, PRF0, PRF70, and PRF92, are studied as the alternatives to diesel, low-octane gasoline-like fuel, and gasoline, respectively. The results show that combustion can be further improved by co-optimizing fuel reactivity, intake temperature and pressure compared to their independent adjustment. Three collaborative optimization strategies are proposed to significantly improve thermal efficiency and HC/CO emissions while maintaining similar PPRR performance and soot emission, indicating the potential to achieve high load extension. In addition, the underlying reasons are revealed by the comparison and analysis of the in-cylinder combustion details. It is found that the increase of intake temperature and pressure results in higher mixing rate and less heat release in high equivalent ratio regions, which is beneficial to the improvement of soot emission. The ignition delay of low reactivity fuel shows higher sensitivity to the variations in intake temperature and pressure, while the overmixing issue of PRF92 at low intake temperature can be significantly improved by applying PRF0 and PRF70. The reasons for the thermal efficiency improvement resulting from low intake temperature and high intake pressure are also presented and discussed from the perspective of energy analysis.