Parameter study of common rail pressure for low octane gasoline multiple premixed compression ignition (MPCI) in light-duty diesel engine

A novel combustion concept called 'multiple premixed compression ignition' in the gasoline direct injection compression ignition regime is proposed. Its predominant feature is the first premixed and subsequent quasi-premixed combustion processes in a sequence of 'spray-combustion-spray-combustion' around the compression top dead center. The multiple-stage premixed combustion decouples the pressure rise from the pollutants formation process, which means the pressure rise rate and emissions can be reduced simultaneously, while achieving a high thermal efficiency. The experimental study of the multiple premixed compression ignition mode has been carried out in a single cylinder research engine retrofitted from a light-duty diesel engine with a compression ratio of 18.5. Low octane gasoline with the research octane number of 66 was tested under 1400 r/min, 0.8 MPa indicated mean effective pressure conditions, without exhaust gas recirculation or intake conditioning. A parameter study of common rail pressure was implemented to investigate its effect on the performance of the multiple premixed compression ignition mode. When the common rail pressure is 60 MPa under the foregoing operating conditions, the shortest ignition delay of the test fuel is observed. In addition, compared to the single-stage diffusion combustion in traditional diesel engines, the multiple premixed compression ignition mode with the test fuel achieves lower emissions of soot, NO and CO, as well as slightly higher indicated efficiency, with a penalty of higher total hydrocarbon emissions.