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A new combustion mode namely multiple premixed compression ignition (MPCI) for gasoline engines was proposed. The MPCI mode can be realized by two or more times gasoline injections into cylinder with a high pressure around the compression TDC and featured with a premixed combustion after each injection in the cylinder, which is different from the existed gasoline direct injection compression ignition (GDICI) modes such as homogeneous charge compression ignition (HCCI) mode with gasoline injection occurred in intake stroke, and partially premixed compression ignition (PPCI) mode with multiple gasoline injections in intake and compression strokes before the start of combustion (SOC). Therefore the spray and combustion of the MPCI mode are alternatively occurred as "spray-combustion-spray-combustion" near the TDC, rather than "spray-spray-combustion" sequence as traditional PPCI gasoline engines.

Fuel quality, including antiknock rating, plays a critical role in enabling optimal operation of advanced gasoline engines. As new designs introduced into the market implement technologies to improve fuel efficiency, the overall octane level of the gasoline pool may need to be increased to ensure optimal performance. Turbocharging, higher compression ratios and downsized displacement all lead to higher combustion pressures and temperatures that make engines more susceptible to knocking. All modern gasoline engines are equipped with knock sensors that detect abnormal combustion resulting from autoignition caused by insufficient octane quality. The ability of an engine to account for the use of lower octane fuel by retarding spark timing and enriching air-fuel ratio to reduce knock is limited, and engine efficiency is directly and adversely impacted when the use of lower octane gasoline is accommodated, resulting in higher fuel consumption.

Two premixed compression ignition modes for low octane gasoline are numerically investigated. The multiple premixed compression ignition (MPCI) mode is featured with a sequence of “spray- combustion- spray- combustion”, while the partially premixed compression ignition (PPCI) mode is a sequence of “spray- spray- combustion”. This paper compares the combustion process of the two modes using multi-dimensional CFD code, KIVA-3v, which can perform chemical reaction calculations for different fuels by a discrete multiple component (DMC) method. The fuel used for simulation consists of 58.5% i-C8H18 and 41.5% n-C7H16 in volume, and has the same RON and similar physical properties to straight-run naphtha used in the experiment. The engine operating condition is fixed at a 1600rpm and 0.7 MPa IMEP. The injection strategies for these two modes are different. All of the parameters in the simulation come from the single cylinder engine experiments.