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An investigation has been carried out to examine the influence of re-entrant combustion chamber geometry on mixture preparation, combustion process and engine performance in a high-speed direct injection (HSDI) four valves 2.0L Ford diesel engine by CFD modeling. The computed cylinder pressure, heat release rate and soot and NOx emissions were firstly compared with experimental data and good agreement between the predicted and experimental values was ensured the accuracy of the numerical predictions collected with the present work. Three ITs (Injection Timing) at 2.65° BTDC, 0.65° BTDC and 1.35° ATDC, all with 30 crank angle pilot separations were also considered to identify the optimum IT for achieving the minimum amount of pollutant emissions.

The mechanism of NOx and soot reduction using different pilot and multiple injection strategies has been computationally studied in a heavy duty DI Diesel engine. A designed set of advanced injection schemes with various variables and exhaust gas recirculation rate (up to 10%) have been analyzed. The CFD model was firstly calibrated against experimental data for a part load operation at 1600 rpm. The computational models used were found to predict the correct trends obtained in the experiment. The study demonstrated the potential and explained the mechanism of the combination of EGR and multiple injection to reduce both soot and NOx emissions together with improved fuel economy.

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.