Abstract
Homogeneous charge compression ignition (HCCI) offers the potential for a significant reduction in NOx emissions and a 20% improvement in fuel economy relative to a port fuel injection spark ignition engine operating at part-load. However, operating an engine in the HCCI mode at light-loads such as idle is difficult to achieve. The objective of this research was to experimentally and computationally investigate the effect of partial oxidation (POx) gas CO and H2 addition on HCCI operation at light-loads. Engine experiments were performed using n-heptane and iso-octane as model fuels to investigate the effect of POx gas on HCCI combustion. The results showed that with n-heptane the addition of POx gas retarded the low temperature chemistry and inhibited autoignition, while with iso-octane POx gas promoted autoignition. Detailed chemical kinetic modeling was performed to gain insight into the important chemistry leading to ignition in an HCCI engine.