Advanced technologies combining turbocharging, downsizing, direct injection, and cooled EGR are being intensively investigated in order to significantly improve the fuel economy of spark-ignition (SI) gasoline engines. To avoid the occurrence of knock and to improve the thermal efficiency, a significant fraction of EGR is often used. Due to the significant fraction of EGR, the ignition source needs to be enhanced to ensure high combustion stability. In addition to advanced spark-based solutions, diesel micro-pilot (DMP) technology has been proposed in recent years where the diesel fuel replaces the spark-plug as the ignition source.
This paper studies the combustion characteristics of a diesel micro pilot ignited gasoline engine, employing direct injection of gasoline and diesel as well as turbocharging and cooled EGR. A multi-dimensional CFD code with a chemical kinetic calculation capability was extensively validated across the engine speed and load range in a previous study . This paper explores the influence of a number of parameters on DMP combustion behavior, including: diesel pilot mass fraction, start of injection (SOI), DMP injection strategy, as well as EGR rate, air/fuel ratio, and DI gasoline/air mixture inhomogeneity.
Besides, the comparison of DMP ignited combustion with traditional spark ignited combustion is also made in terms of EGR tolerance, lean burn limit, and DI gasoline air mixture inhomogeneity. Finally, numerical simulations aimed at optimizing both gasoline and diesel injection parameters, as well as EGR rate in order to enhance the engine performance in the DMP combustion mode, are discussed.