Numerical simulations of direct injection (DI) heavy-duty diesel engine combustion over the entire engine operating range were conducted using the KIVA code, with modifications to the spray, combustion, turbulence, and heat transfer models. In this work, the effect of the rates of species conversion from reactants to products in the combustion model was investigated, and a characteristic time combustion model was formulated to allow consideration of multiple characteristic time scales for the major chemical species. In addition, the effect of engine operating conditions on the model formulation was assessed, and correlations were introduced into the combustion model to account for the effects of residual gas and Exhaust Gas Recirculation (EGR). The predictions were compared with extensive engine test data. The calculation results, had good overall agreement with the experimental cylinder pressure and heat release results, and the multiple-time-scale combustion model is shown to give improved emissions predictions compared to a previous single-time-scale model. Overall, the NOx predictions are in good agreement with the experiments. The soot predictions are also in reasonable agreement with the measured particulates at medium and high loads. However, at light loads, the agreement deteriorates, possibly due to the neglect of the contribution of SOF in the soot model predictions.

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