This study improved the computational efficiency significantly using parallel computation and reduced mechanisms. A 3-dimensional engine moving mesh of intake port, exhaust port and combustion chamber was established for HCCI engine cycle simulation. To achieve a more accurate analysis, chemical kinetics was implemented into the CFD code to study the intake, spray, ignition, combustion, and pollution formation process in HCCI engine.
The simulations were run on a cluster of 16-CPU, parallelized by Message-Passing Interface (MPI) mode. The cases with detailed and reduced reaction mechanisms were calculated using 1, 2, 4, 8, 16 CPUs respectively and the corresponding computational time and speed-up were discussed. Using MPI 8-CPU with reduced mechanism (less than 40 species) is the optimal scheme for CFD/Chemistry calculation of typical HCCI engine. For single-cycle HCCI engine simulation, the calculation time of 1-CPU case with detailed mechanism was reduced from 1 month to 1 day (22 hours) compared to that of MPI 8-CPU with reduced mechanism.
Based on parallel computation, HCCI combustion processes with different equivalence ratios were analyzed, the effects of load on HCCI ignition, combustion and emission were studied. The results show that temperature stratification leads to sequential heat release during HCCI combustion process. Furthermore, HCCI engine cycles with two-stage direct injection strategies were parametrically simulated to provide a detailed insight into HCCI combustion and emission process. This study gives better understanding to the HCCI combustion process and provides useful guide for combustion optimization in HCCI engine.