The Development and Application of Homogeneity Factor on DI Diesel Engine Combustion and Emissions

An improved parameter called “Homogeneity Factor (HF) of in-cylinder charge” has been introduced as a measure to quantify the quality of the air-fuel mixing process in diesel engines. For this purpose, a CFD simulation has been performed to evaluate the effects of Homogeneity Factor on different injection strategies and its correlation with pre mixing process in a common rail DI diesel engine. The results showed a higher Homogeneity Factor will result in higher rate of air-fuel mixing and more complete combustion process. However, the careful adjustment must be made for ideal reduction for both NOx and soot emissions. It was also found when the dwell delay between injection pulses becomes longer, it leaves more time for the air-fuel mixing and initial combustion process of first injection pulse and therefore, the increase of Homogeneity Factor takes place at a later stage and it can caused a reduction of NOx formation. In addition, with later injection timings the combustion process might also be shifted into the expansion stroke and thus the temperature level will be lowered.