Use of advanced fuel injection strategies for emissions reduction in diesel engines

Emissions reduction in diesel engines can be achieved through a number of advanced combustion strategies, including multiple fuel injections and fuel injection rate shaping techniques. These fuel injection strategies reduce emissions, including soot, NO_x, and unburned hydrocarbons, by manipulating fuel/air mixtures and local equivalence ratios, local temperatures and cylinder pressure, as well as overall combustion phasing. This work seeks to describe the mechanisms by which multiple injection strategies reduce unburned hydrocarbons at low-temperature combustion conditions. The results show that unburned hydrocarbon emissions are reduced when multiple injections are used, and when combustion timing is thermodynamically favorable. Although multiple injection strategies can reduce unburned hydrocarbons at thermodynamically unfavorable timings, when injection occurs during the expansion stroke, the multiple injections are less effective at these conditions. The results indicate that both mixture preparation and thermal conditions have a significant effect on emissions. Future directions of research for internal combustion engines and turbulent reacting flows in general are outlined to address the challenges associated with predicting emissions from highly unsteady reacting flows.