High Efficiency and Low Pollutants Combustion: Gasoline Multiple Premixed Compression Ignition (MPCI) 2012-01-0382

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. Since the combustion process of the MPCI mode is mainly controlled by the multiple gasoline injections, the SOC and pressure rise rate (PRR) can be controlled easily and effectively through injection timing, injection split ratio and number of the injections. It is expected that each premixed combustion process in the MPCI engine can be realized in the center of combustion chamber with pure air filling the gap between the combustion area and the cylinder wall, resulting in not only the low PM and NOx emissions, but also the low THC and CO emissions while remaining the high thermal efficiency.

The experimental study for the MPCI gasoline engine is carried out on a single-cylinder compression ignition engine retrofitted from a four-cylinder light-duty diesel engine with the compression ratio of 18.5. A stable and moderate two-stage gasoline MPCI mode is achieved under the running conditions of 0.8 MPa IMEP load and 1400 r/min speed at 70°C intake temperature without EGR and intake boosting using the gasoline fuel with the research octane number of 94.4. The NO and soot emissions as well as THC and CO are relatively low, while keeping the indicated thermal efficiency around 40%, which cannot be easily reached with even diesel fuel under the same conditions. However, optimization for the gasoline MPCI combustion mode is still needed in order to improve the fuel efficiency further. The test results show that the MPCI mode is a promising and feasible combustion mode for gasoline engines achieving both of the high efficiency and low emissions especially at high load.