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. In order to investigate the effect of combustion chamber, thirteen different types of combustion chamber configurations have been considered based on four categories including piston bowl depth, piston bowl width, and piston bottom surface and lip area. For all the studied cases, compression ratio, squish bowl volume and the amount of injected fuel were kept constant to avoid that the effects of changes in chamber geometry be masked by the effect of other engine parameters. The results confirmed that the combustion chamber geometry has significant effects on the combustion process. It showed that by changing the design of the piston crown, the amount of emission pollutants can be decreased while the other performance parameters of engine remain constant.

Effects of included spray angle with different injection strategies on combustion characteristics, performance and amount of pollutant emission have been computationally investigated in a common rail heavy-duty DI diesel engine. The CFD model was firstly validated with experimental data achieved from a Caterpillar 3401 diesel engine for a conventional part load condition at 1600 rev/min. Three different included spray angles (α = 145°, 105°, 90°) were studied in comparison with the traditional spray injection angle (α = 125°). The results show that spray targeting is very effective for controlling the in-cylinder mixture distributions especially when it accompanied with various injection strategies. It was found that 105° spray cone angle along with an optimized split pre- and post-Top Dead Center (TDC) injection strategy could significantly reduce NOx and soot emissions without much penalty of the fuel consumption, as compared to the wide spray angle. In addition, a narrow injection angle offers more efficient air-mixing process due to better interaction with the combustion chamber and cylinder liner.