Modeling the effects of fuel injection characteristics on diesel combustion and emissions.

摘要

A new set of spray submodels, which improve the performance of the KIVA-II computer code under diesel engine operating conditions, is introduced in this study. This set of submodels improves the droplet drag and droplet breakup predictions, and offers an alternative to the built-in evaporation and collision models. The performance of the new models is verified using non-evaporating and evaporating spray bomb experiments, along with diesel engine experiments. In the non-evaporating cases, detailed comparisons of the droplet size predictions with optically measured droplet sizes show the validity of the new breakup, drag, and coalescence models. In the evaporating cases, comparisons of the fuel liquid and vapor penetration with model predictions are used to validate the models. The engine cases test the validity of the model under typical diesel engine conditions, where comparisons of the pressure, heat release rate, and predicted engine-out emissions are used to further validate the models. The models presented provide an accurate means of predicting spray behavior under diesel engine conditions. With the adjustment of two spray constants, which account for the behavior of a particular injector, accurate predictions of the spray droplet sizes and locations, the vaporization rate, and the resulting combustion and emissions production are now possible. With the constants fixed for a given injector, the trend in nitrous-oxide and soot formation can be predicted, even when a complex injection scheme, such as a split injection, is employed.