CFD investigation into diesel fuel injection schemes with aid of Homogeneity Factor

A modified parameter named " Homogeneity Factor (HF) of in-cylinder charge" has been introduced as a new measure for supporting the understanding of the air-fuel mixing and combustion process in diesel engines. The effects of this parameter on engine performance and pollutant emissions have been studied using various EGR and split injection schemes on a DI diesel engine. In this study, twelve different injection strategies for which two injection pulses with different fuel amount for each pulse (up to 30% for the second pulse) and different separation between two pulses (up to 30° CA) were evaluated using CFD modeling. Results show the higher Homogeneity Factor will result in higher rate of air-fuel mixing and more complete combustion process. It was found when the dwell delay between injection pulses becomes longer, as it leaves more time for the air-fuel mixing during the late compression stroke, the maximum amount of Homogeneity Factor will be obtained at a later stage of combustion process and it can caused a reduction of NOx formation. This suggests, by optimizing split injection configurations accompanied with appropriate EGR rate, pollutant emissions can be decreased and controlled more accurately.