Abstract
The CAI engine, a kind of HCCI engine, as a new type of gasoline engine is one of the eco-friendly engines. The main merits of CAI engines are low NO_x emission and fuel economy. Combustion of CAI engine is purely dominated by fuel chemical reactions. In order to simulate the combustion of CAI engine, a reduced chemical kinetic mechanism of gasoline surrogate and multi-zone method is proposed in this paper. A reduced chemical kinetic mechanism for a gasoline surrogate was validated in this study for a CAI combustion. This gasoline surrogate was modeled as a blend of iso-octane, n-heptane, and toluene. This reduced mechanism consists of 49 species and 67 reactions and it includes main reaction paths of iso-octane, n-heptane, and toluene. A RCM was used for the validation of this reduced mechanism and matched with the modeling of the RCM using STAR-CD. The results of the experiment and the simulation showed good agreement. For the analysis of CAI combustion, a multi-zone method was developed and incorporated into the computational fluid dynamics code, STAR-CD. This coupled multi-zone model can calculate 3 dimensional computational fluid dynamics and multi-zoned chemical reaction simultaneously in one time step. In other words, every computational cell interacts with the adjacent cells during the chemical reaction process. The effect of the EGR gas uniformity and equivalence ratio were studied. In the same EGR gas quantity, EGR distribution could affect on engine performance. EGR leaned to cylinder wall could lower the pressure rise rate, so it can be adopted to solve the noise and vibration problem of CAI engines. Equivalence ratio has very sensitive influence in bulk temperature.
