Parametric Study Based on a Phenomenological Model to Investigate the Effect of Post Fuel Injection on HDDI Diesel Engine Performance and Emissions-Model Validation Using Experimental Data

A major challenge for researchers and engineers in the field of diesel engine development is the simultaneous reduction of both NOx and soot emissions from diesel engines to comply with strict future emission legislation. One of the promising internal measures that focus on the reduction of soot emissions is post fuel injection which does not have a serious effect on NOx emissions. The main parameters involved when using this technique are post fuel quantity and dwell angle between the main and the post fuel injection events. In the present work a detailed computational investigation has been conducted to determine the effect of post fuel injection on engine performance and pollutant emissions (NOx and soot). To this scope, a phenomenological multi-zone combustion model has been used, properly modified to take into account the interaction of post and main injected fuel amounts. Using the proposed model a parametric study has been conducted varying both post fuel injection quantity and dwell angle and maintaining model's constants the same when switching from normal to post injection. From this analysis it is revealed that post fuel injection enhances soot oxidation due to the increase of in-cylinder temperature at the late phase of combustion cycle, and mainly due to the improved air-fuel mixing as a result of the post injection mechanism. To validate the model various performance parameters and exhaust tailpipe values are compared with experimental data obtained from measurements performed on a heavy duty turbocharged DI Diesel engine, equipped with a common rail fuel injection system with and without post injection. As observed the model manages in general to capture the effect of both post injection parameters examined on engine performance and emissions despite differences observed in absolute values for some cases. Furthermore, information is provided for soot formation and oxidation rates and the actual effect of post injection upon them.