Effects of Heterogeneous EGR on the Natural Gas Fueled HCCI Engine Using Experiments, CFD and Detailed Kinetics

HCCI (Homogeneous Charge Compression Ignition) combustion has attracted attention as a new combustion technology, owing to its capability of achieving both low NOx and high efficiency. However, issues of ignition control and high-load operations still remain. As a possible solution to these problems, the present authors have attempted to devise a combustion control method using EGR on natural gas-fueled HCCI engines. Effects of EGR on HCCI combustion have been studied from experimental and numerical simulation fronts. Results of knock suppressing effects using EGR to increase operation load of HCCI combustion were reported elsewhere. In the present study, effects of inhomogeneity of EGR inside the cylinder on HCCI combustion are reported by performing experiments, CFD and detailed chemical kinetics calculations. When EGR gas is densely distributed near the wall of the cylinder, i.e., in lower temperature zone, combustion is found to be enhanced compared to the cases in which EGR gas is homogeneously distributed. When EGR gas is concentrated near the cylinder center (higher temperature zone), combustion becomes slower than in the cases of homogeneous EGR gas distribution.