Impact of fuel and injection system on particle emissions from a GDI engine

In recent years, particulate emissions from the gasoline direct injection (GDI) engine, especially the ultrafine particulates, have become a subject of concern. In this study, the impact of fuel (gasoline versus ethanol) and injection system (injection pressure and injector condition) on particle emissions was investigated in a single cylinder spray-guided GDI research engine, under the operating conditions of stoichiometric air/fuel ratio, 1500 rpm engine speed and 3.5-8.5 bar IMEP. The results show that, in a spray guided GDI engine, ethanol combustion yields much lower particle mass (PM) but higher particle number (PN) emissions, compared to gasoline. Depending on the fuel used, the PM and PN emissions respond differently to injection pressure and injector condition. For gasoline, the injection system has a significant impact on the PM and PN emissions. High injection pressure and clean injector condition are both essential for low particle emissions. Compared to gasoline, the particle emissions from ethanol combustion is less sensitive to the injection system, due to its higher volatility and diffusive combustion which produces less soot. Furthermore, a PM and PN trade-off was observed when using gasoline and ethanol, and when using high injection pressures.