Numerical Study of the RCCI Combustion Processes Fuelled with Methanol, Ethanol, n-Butanol and Diesel

In the current, numerical study RCCI combustion and emission characteristics using various fuel strategies are investigated, including methanol, ethanol, n-butanol and gasoline as the low reactivity fuel, and diesel fuel as the high reactivity fuel. A reduced Primary Reference Fuel (PRF)-alcohol chemical kinetic mechanism was coupled with a computational fluid dynamic (CFD) code to predict RCCI combustion under various operating conditions. The results show that a higher quantity of diesel was required to maintain the same combustion phasing with alcohol-diesel fuel blends, and the combustion durations and pressure rise rates of methanol-diesel (MD) and ethanol-diesel (ED) cases were much shorter and higher than those of gasoline-diesel (GD) and n-butanol-diesel (nBD) cases. The simulations also investigated the sensitivities of the direct injection strategies, intake temperature and premixed fuel ratio on RCCI combustion phasing control. Compared to GD and nBD cases, the combustion phasing of MD and ED is less sensitive with single injection strategies, but are more sensitive to the premixed fuel ratio. The combustion phasing of ED and GD cases exhibited the least sensitivity with double injection strategies and intake temperature, respectively. When comparing the emissions of different fuels, NOx and soot emissions increased with the increase of DI mass at low load conditions, while the soot emissions decreased with the increase of fuel oxygen content at higher load conditions.