Oxides of Nitrogen from Direct Injection Diesel Engines

Abstract

Many models for the prediction of emissions and combustion based on the phenomenology of spray combustion for DI diesel engines are available in the literature. All of them utilized empirical heat transfer correlation, which is mass averaged. Experimental observations from modern diesel engines of heavy-duty application showed that NO_x formation suppresses at higher loads although favourable conditions exist. A new phenomenological model for NO_x emission is developed based on mixing-controlled combustion incorporating localized wall heat transfer. In this work, a phenomenological model for heat transfer from wall–spray is also proposed which is employed along with the heat release model to account for the effect of localized heat transfer. A simple geometrical relation is employed for the spray–wall interaction and subsequent turbulence structure for spray developed earlier by the authors. This model is one-dimensional and does not need any engine-specific tuning. The newly evolved NO_x model takes into consideration all the engine operating parameters, viz. engine speed, fuel injection pressure, intake air pressure, temperature and swirl number, etc. The effects of exhaust gas recirculation and biodiesel on NO_x formation are also incorporated in this model. The new model was validated by conducting experimental investigations on 6 engines at different operating conditions with widely varying features.