Effects of Injection Pressure and Nozzle Geometry on D.I. Diesel Emissions and Performance 950604

An emissions and performance study was performed to show the effects of injection pressure, nozzle hole inlet condition (sharp and rounded edge) and nozzle included spray angle on particulate, NOx, and BSFC. The tests were conducted on a fully instrumented single-cylinder version of the Caterpillar 3406 heavy duty engine at 75% and 25% load at 1600 RPM. The fuel system consisted of an electronically controlled, hydraulically actuated, unit injector capable of injection pressures up to 160 MPa. Particulate versus NOx trade-off curves were generated for each case by varying the injection timing. The 75% load results showed the expected decrease in particulate and flattening of the trade-off curve with increased injection pressure. However, in going from 90 to 160 MPa, the timing had to be retarded to maintain the same NOx level, and this resulted in a 1 to 2% increase in BSFC. The rounded edged nozzles were found to have an increased discharge coefficient. By adjusting the injection pressure, it was possible to compare the performance of the rounded and sharp edged nozzles with the same mass rate of injection profiles. Interestingly, the sharp edged nozzle gave significantly lower particulate emissions and lower BSFC at lower injection pressures. However, as the injection pressure was increased the difference in particulate became smaller and the rounded edged nozzles gave lower BSFC. Two nozzle spray angles with included angles of 125 and 140 degrees were studied. The effects of spray angle on particulate and NOx emissions was found to be small at high load, but differences were seen at light load. These results are interesting because the spray in the 125 degree case is directed so as to give significant spray impingement on the piston bowl wall, while the 140 degree nozzle has minimal wall impingement.