Acceleration of Detailed Chemical Kinetics Using Multi-zone Modeling for CFD in Internal Combustion Engine Simulations

Detailed chemical kinetics, although preferred due to increased accuracy, can significantly slow down CFD combustion simulations. Chemistry solutions are typically the most computationally costly step in engine simulations. The calculation time can be significantly accelerated using a multi-zone combustion model. The multi-zone model is integrated into the CONVERGE CFD code. At each time-step, the CFD cells are grouped into zones based on the cell temperature and equivalence ratio. The chemistry solver is invoked only on each zone. The zonal temperature and mass fractions are remapped onto the CFD cells, such that the temperature and composition non-uniformities are preserved. Two remapping techniques published in the literature are compared for their relative performance. The accuracy and speed-up of the multi-zone model is improved by using variable bin sizes at different temperature and equivalence ratios. In addition, a general n-dimensional zoning strategy is developed to include other cell variables such as pressure, mass fractions of different species, etc. to improve the performance of the zoning strategy. This paper discusses the savings in computational time achieved and the accuracy of the results using the multi-zone model for a range of scenarios. Gasoline and Diesel engine simulations are performed. Test cases are run for single fuel and multi-component fuels. Exhaust gas recirculation (EGR) scenarios are also tested.