Effects of temperature inhomogeneities on the HCCI combustion in an optical engine

This work investigated the influence of temperature inhomogeneities on the HCCI combustion process through an optically accessible engine. Temperature inhomogeneities were formed by changes in piston bowl geometries, intake temperatures, coolant temperatures. Results showed that combustion chamber geometry could play an important role in HCCI combustion. The autoignition for the reentrant bowl (A-type) combustion chamber always occurred at the center of the combustion chamber even with different intake temperatures and coolant temperatures. However, the autoignition for salient bowl (V-type) combustion chamber was more dispersive and closer to the chamber wall compared to A-type. For the V-type combustion chamber, the peak value of the heat release rate and the pressure rise rate was the highest and the combustion duration was the shortest among three cases, because of the piston bowl forming a lower turbulence intensity; while A-type combustion chamber induced a higher turbulence intensity, which enhanced the temperature inhomogeneities in the piston bowl, leading to moderate pressure rise rate and heat release rate. Turbulence intensity control offered a potentially effective approach to modulating the combustion process in HCCI engines.