MULTIDIMENSIONAL MODELING OF COMBUSTION FOR A 6-MODE EMISSIONS TEST CYCLE ON A DI DIESEL-ENGINE

Numerical simulations of direct injection (DI) heavy-duty diesel engin e combustion over the entire engine operating range were conducted usi ng the KIVA code, with modifications to the spray, combustion, turbule nce, and heat transfer models. In this work, the effect of the rates o f species conversion from reactants to products in the combustion mode l was investigated, and a characteristic-time combustion model was for mulated to allow consideration of multiple characteristic time scales for the major chemical species. In addition, the effect of engine oper ating conditions on the model formulation was assessed, and correlatio ns were introduced into the combustion model to account for the effect s of residual gas and Exhaust Gas Recirculation (EGR). The predictions were compared with extensive engine test data. The calculation result s has good overall agreement with the experimental cylinder pressure a nd 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 agr eement with the experiments. The soot predictions are also in reasonab le agreement with the measured particulates at medium and high loads. However, at light loads, the agreement deteriorates, possibly due to t he neglect of the contribution of SOF in the soot model predictions.