In order to enhance the thermal efficiency of gasoline engines, a combustion mode namely Homogeneous Charge Induced Ignition (HCII) was introduced and examined in this paper. Port-injected gasoline was used as the main fuel and formed a homogeneous charge in the cylinder. Diesel was used as the pilot fuel, directly injected into the cylinder, and self-ignited and this induced the ignition of the premixed gasoline-air charge.
The images of HCII combustion process were taken on an optical engine through a high-speed CMOS camera. The multi-point induced ignition phenomena were observed and the parameters like flame luminance, ignition delay and combustion duration were analyzed by image analysis. The result shows that as the gasoline/diesel ratio increases with a fixed low pilot amount, the ignition delay increases, the initial ignition area extends from the center towards the periphery of the combustion chamber, and the combustion velocity increased.
The characteristics of the HCII mode was also examined on a modified four-cylinder diesel engine. Fuel consumption, combustion and emission characteristics were studied and compared with the original diesel. The result shows that at high load, HCII mode can increase the thermal efficiency of gasoline to the level of a diesel. NOx emissions from the engine are lower than that from a diesel and smoke can be greatly reduced to near zero. The effects of HCII mode on PM and SOF emissions were also examined through a PM sampling equipment and the extraction method.