Gasoline multiple premixed compression ignition (MPCI): Controllable, high efficiency and clean combustion mode in direct injection engines

A novel combustion concept namely “multiple premixed compression ignition” (MPCI) in gasoline direct injection compression ignition (GDICI) regime is proposed. Its predominant feature is the first premixed and followed quasipremixed combustion processes in a sequence of “spray-combustion-spray-combustion”. The multiple-stage premixed combustion decouples the pressure rise with pollutants formation process, which means the pressure rise rate and emissions can be reduced simultaneously, while achieving a high thermal efficiency. The gasoline MPCI mode has been demonstrated in a research engine with a compression ratio of 18.5. Gasoline with the research octane number (RON) of 94.4 was tested under 1400 rpm, 0.6 MPa IMEP conditions, without EGR and intake boosting. A parameter study of common rail pressure and intake temperature was implemented to investigate their effects on the performance of MPCI mode. Compared to the single-stage diffusion combustion in traditional diesel engines, the gasoline MPCI mode achieves lower emissions of soot, NO, CO, as well as slightly higher indicated efficiency, with a penalty of higher THC emissions when the common rail pressure is larger than 80 MPa in this study. With intake temperature sweeping, the gasoline MPCI mode also has the foregoing advantages compared to the diesel under the same operating conditions.