Experimental and Modelling Investigations of the Gasoline Compression Ignition Combustion in Diesel Engine

In this work the gasoline compression ignition (GCI) combustion characterized by both premixed gasoline port injection and gasoline direct injection in a single-cylinder diesel engine was investigated experimentally and computationally. In the experiment, the premixed ratio (PR), injection timing and exhaust gas recirculation (EGR) rate were varied with the pressure rise rate below 10 bar/crank angle. The experimental results showed that higher PR and earlier injection timing resulted in advanced combustion phasing and improved thermal efficiency, while the pressure rise rates and NOx emissions increased. Besides, a lowest ISFC of 176 g/kWh (corresponding to IMEP =7.24 bar) was obtained, and the soot emissions could be controlled below 0.6 FSN. Despite that NOx emission was effectively reduced with the increase of EGR, HC and CO emissions were high. However, it showed that GCI combustion of this work was sensitive to EGR, which may restrict its future practical application. For modelling investigation, the primary reference fuel (92% isooctane and 8% n-heptane, PRF92) was used as a surrogate of commercial RON92 gasoline fuel for combustion prediction. The combustion and emission characteristics were reasonably predicted. Control parameters, including premixed ratio, injection timing and EGR rate on the GCI combustion process were further elucidated. It demonstrated that the GCI combustion was initiated by the spray periphery near the cylinder bowl. NOx was mainly formed in the spray periphery rather than the homogeneous region, while soot was formed in the downstream of the spray.