Diesel Emission Characteristics Using High Injection Pressure with Converging Nozzles in a Medium-Duty Engine

Effects of high injection pressure and converging nozzles on combustion and emissions of a multi-cylinder diesel engine were investigated. The engine uses a common-rail injection system that allows a maximum injection pressure of 200 MPa. Various injection pressures were tested to explore the benefits of high injection pressure in achieving low exhaust emissions in diesel engines. Injectors used in this study include conventional straight-hole nozzles and converging nozzles with a K factor of 3. Parametric studies were performed including variations in injection timings, number of injection pulses and EGR levels. It was found that low temperature combustion can be achieved by using high EGR with 1) late single injection or 2) double injection with an early pilot and a late main injection. Investigations revealed that high injection pressures significantly reduced soot emissions with an increase in NOx emissions under conventional injection timing ranges. However, under late injection conditions (i.e., SOI=5 ATDC), an increase in the injection pressure from 150 MPa to 200 MPa did not result in further soot reduction. The use of injectors with converging nozzles allows achieving a higher injection pressure due to better flow coefficients. However, the effect on overall emission reduction was not significant for the converging nozzle used in this study.