Modeling the Effects of EGR and Injection Pressure on Emissions in a High-Speed Direct-Injection Diesel Engine

Experimental data is used in conjunction with multi-dimensional modeling in a modified version of the KIVA-3V code to characterize the emissions behavior of a high-speed, direct-injection diesel engine. Injection pressure and EGR are varied across a range of typical small-bore diesel operating conditions and the resulting soot-NO_x tradeoff is analyzed. Good agreement is obtained between experimental and modeling trends; the HSDI engine shows increasing soot and decreasing NO_x with higher EGR and lower injection pressure. The model also indicates that most of the NO_x is formed in the region where the bulk of the initial heat release first takes place, both for zero and high EGR cases. The mechanism of NO_x reduction with high EGR is shown to be primarily through a decrease in thermal NO_x formation rate.