he issue of energy and pollutant emissions has become more prominent over the past few years. Increasingly, power sources with high efficiency and low emissions are in demand. The application of oxygen-enriched air in diesel engines has been proven to be an effective in-cylinder strategy for soot reduction and to improve combustion effectiveness. This however results in an increase in the NOx level. A simulation study using a three-dimensional computational fluid dynamics (CFD) model has been conducted to investigate the effects of oxygen-enriched air on a DI diesel engine operating in order to reduce soot emissions with minimal changes in NOx emissions. A parametric study has been initially performed to examine the impact of intake air oxygen content from 21% to 35% v/v under constant fueling rate. Then sixteen different strategies have been proposed to consider the effects of intake air oxygen fraction from 21% to 25% under four different fueling rates. In this study, 24% O2 were found to achieve the best-operating conditions for engine performance and reduced NOx emissions.