Multi-Zone Combustion Modelling for the Prediction of Pollutants Emissions and Performance of DI Diesel Engines

In the past years various models have been proposed for the modelling of performance and pollutants emissions from DI diesel engines. These models range from complicated 3D detailed ones up to simple two zone phenomenological ones. The latter ones although simple offer solutions in engine study and are widely used due to their low computational cost and simplicity. In the present work a multi-zone model for direct injection diesel engines is presented together with its application on a direct injection diesel engine located at the authors laboratory. Multi-zone models usually fail to predict adequately both pollutants emissions and performance and thus focus mainly on pollutants emissions. Of course this is not acceptable since the formation of pollutants is strongly related to the combustion mechanism. In the present work an effort has been made to overcome this problem and predict both performance and emissions throughout the engine operating range. To validate the model an extensive experimental investigation has been conducted on a high speed DI diesel engine located at the authors laboratory. By comparing the theoretical results with the experimental ones it is revealed that the model predicts with reasonable accuracy nitric oxides, soot emissions and performance as well. Also information is derived from the model concerning the areas inside the fuel jet where these pollutants are formed, offering thus a better understanding of the mechanisms that lead to their formation. Information is also provided concerning the evolution of the jet and the pollutants concentration in it with respect to time (engine crank angle), revealing the phases where the pollutants are formed. The proposed model requires very low computational time of about 1 min for a complete run. so that it is suitable for the optimisation of existing engines and the development of new ones.