Research on spark induced compression ignition (SICI)

Spark induced compression ignition (SICI) is a practical control technology for ignition enhancement in gasoline HCCI combustion. In this paper, SICI combustion mechanism was studied using combustion visualization, engine test and numerical simulation respectively. It provided a useful combustion optimization guide for gasoline HCCI engines. Firstly, the ignition process of SICI was captured by combustion visualization in an optical engine. The results show that SICI is a combined combustion mode with partly flame propagation and main auto-ignition. The spark ignites the local mixture near the spark electrodes and flame propagation occurs before the homogeneous mixture auto-ignition. Heat release from the burned zone due to flame propagation which increases the in-cylinder pressure and temperature, and causes the entire mixture auto-ignition. Furthermore, three combustion modes, including HCCI, SICI, SI, were investigated on a gasoline direct injection (GDI) engine with high compression ratio and switchable cam-profiles. The results show that SICI has obvious combustion characteristics with two-stage heat release and lower pressure rise rate. This combined combustion mode can be utilized as effective method for high load extension on gasoline HCCI engines. The maximum IMEP of 0.82MPa can be achieved with low NOx emissions and high thermal efficiency under stoichiometric condition. Finally, numerical simulation was carried out on SICI combustion using improved CFD code. It indicates that spark ignition can trigger HCCI with a little NOx increase.