Modeling Combustion and Emissions of HSDI Diesel Engines Using Injectors with Different Included Spray Angles

Combustion in an HSDI diesel engine using different injectors to realize low emissions is modeled using detailed chemical kinetics in this study. Emission characteristics of the engine are investigated using injectors that have different included spray angles, ranging from 50 to 130 degrees. The engine was operated under PCCI conditions featuring early injection times, high EGR levels and high intake temperatures. The Representative Interactive Flamelet (RIF) model was used with the KIVA code for combustion and emission modeling. Modeling results show that spray targeting plays an important role in determining the in-cylinder mixture distributions, which in turn affect the resulting pollutant emissions. High soot emissions are observed for injection conditions that result in locally fuel rich regions due to spray impingement normal to the piston surface. Soot emissions can be reduced if the injection angle and timing can be better coordinated with squish flows and/or spray-induced flows to prevent the formation of fuel rich regions. In general, a soot and NOx trade-off is observed with respect to the start-of-injection timing. The unburned hydrocarbon and CO are found to reside in the same regions as high soot concentrations. This indicates that the sources of CO and HC are the incomplete combustion of fuel rich mixture in the present HSDI diesel engine.