Multi-zone phenomenological model of combustion and emission characteristics and parametric investigations for split injections and multiple injections in common-rail direct-injection diesel engines

This paper presents the formulation of a multi-zone zone phenomenological model for predicting the combustion and emission characteristics of split-injection and multiple-injection common-rail direct-injection diesel engines. In this model, the instantaneous combustion space is divided into two regions, namely the spray zones and the surrounding air. The model predictions for combustion and emissions for split injections and multiple injections are validated with the measured results on a wide range of injection schedules available in the literature. The comparisons reveal the good predictive ability of the model with reasonable accuracy and demonstrate the applicability of the multi-zone model to multiple-injection common-rail direct-injection engines. Hence, the model is used for parametric investigations to analyse the effect of split injections and multiple injections on the combustion and emission characteristics of common-rail direct-injection diesel engines. The parametric investigations show that an increase in the pilot fuel quantity increases the nitrogen oxide emissions and reduces the soot emissions while the dwell period has to be optimized for simultaneous reductions in the nitrogen oxide emissions and the soot emissions. Therefore the present model can be used to achieve an optimal injection schedule for given engine operating conditions.