Potential of Stratification Charge for Reducing Pressure-Rise Rate in HCCI Engines Based on Multi-Zone Modeling and Experiments by using RCM

The charge stratification has been thought as one of the ways to reduce the sharp pressure rises of HCCI combustion. The objective of this study is to evaluate the potential of equivalence ratio, initial temperature, and EGR gas stratifications for reducing pressure-rise rate of HCCI combustion. Using rapid compression machine, the stratified pre-mixture is charged, and compressed to analyze the change of in-cylinder gas pressure and temperature traces during compression process. Based on the experiment results, numerical calculations by CHEMKIN are conducted to more specifically analyze the potential of equivalence ratio, initial temperature, and EGR gas stratifications on the reduction of pressure rise rate. Multi-zone model is used to simulate the thermal stratification, fuel stratification and EGR gas stratification of in-cylinder charge as like real engine. Then, the results from multi-zone model are compared with that from single-zone model to clearly verify the effects of three stratifications on pressure-rise rate. The results from comparison between single-zone model and multi-zone model show that EGR gas stratification was the most effective to disperse ignition timing compared to the thermal stratification and fuel stratification when setting the same time differences of ignition timing shown in single-zone model. Among the three stratifications of in-cylinder charge, fuel stratification was the worst to disperse of ignition timing.