Numerical Investigation of Multi-Stage HCCI Combustion with Small Chamber Inside Piston

Homogeneous charge compression ignition (HCCI) combustion is promising for not only high thermal efficiency but also reducing nitrogen oxides (NOx) and PM simultaneously. However, the operational range of the HCCI combustion is limited because of some issues, such as poor control of ignition timing and knocking by the excessive rate of pressure rise. In this study, a new combustion system based on the HCCI combustion process is proposed based on the authors' previous experimental work. This combustion system has a divided combustion chamber of two parts, one is small and the other is large. The most significant feature is the small chamber inside the piston. At first, combustion takes place in the small chamber, and then the burned gas is ejected into the large chamber to ignite the mixture in the large chamber. In this combustion system, the combustion in the large chamber takes the HCCI combustion process. 3D-CFD was conducted to predict HCCI combustion characteristics with small chamber inside the piston, varying the geometry of small chamber. Simulation results revealed that this combustion system can be achieve two-stage HCCI combustion with reduced pressure rise rate.