Modeling and Experiments of Dual-Fuel Engine Combustion and Emissions

The combustion and emissions of a diesel/natural gas dual-fuel engine are studied. Available engine experimental data demonstrates that the dual-fuel configuration provides a potential alternative to diesel engine operation for reducing emissions. The experiments are compared to multi-dimensional model results. The computer code used is based on the KIVA-3V code and consists of updated sub-models to simulate more accurately the fuel spray atomization, auto-ignition, combustion and emissions processes. The model results show that dual-fuel engine combustion and emissions are well predicted by the present multi-dimensional model. Significant reduction in NO_x emissions is observed in both the experiments and simulations when natural gas is substituted for diesel fuel. The HC emissions are under predicted by numerical model as the natural gas substitution is increased. The capabilities and limitations of the combustion model to simulate premixed combustion of air and natural gas were identified. It was found that the combustion model previously developed for diesel combustion provides adequately accuracy when extended to model the present dual-fuel cases. However, the accuracy of the predictions deteriorates for small pilot quantities. A brief discussion is given of a new combustion modeling approach that is applicable to very low pilot diesel fuel cases.