Abstract
It is becoming evident that the fuel-air mixing process in high pressure multiple-injection CRDI engines is different from the conventional single injection such that a simultaneous reduction between NOx and soot particulate emissions is realizable. As a novelty, this paper explores the physics behind the mixing processes in multiple-injection technique using a comprehensive phenomenological model developed and validated by the authors for predicting combustion and emissions characteristics of multiple-injection CRDI engines. Towards this objective, the paper predicts and relates the variations in mixing rates for double and triple injection schedules with their observed combustion and emission characteristics. These quantitative predictions of mixing rates in multiple-injection substantiate the cause of soot reduction during later part of CRDI combustion. The predictions of fuel evaporation, fuel air mixing and emission characteristics of high pressure multiple-injection CRDI engines obtained from the model are found to reveal features useful in understanding CRDI engine performance. The trends and relationship of injection and its related processes observed in this study conform to the experimental observations of several multiple-injection CRDI engine studies. The predictions from the model suggest that there must be an optimal injection schedule in order to achieve the simultaneous reduction of nitric oxide and soot particulate emissions with the minimum sacrifice on fuel economy.
