Cfd Analysis On Performance And Emissions In Di Diesel Engine With High Pressure Injections
Keywords: NOX , particulate matter ,computational fluid dynamics .start of injection, duration of injections
ABSTRACT: 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 Simulations were conducted on a fully instrumented single-cylinder version of the Caterpillar 3406 heavy duty engine at 75% and 25% load at 1600 RPM. Commercial validation tool FLUENT was used for numerical simulation. This tool solves the basic governing equations of fluid flow that is continuity, momentum, species transport and energy equation. Using finite volume method Turbulence was modeled by using standard k-έ model. Injection was modeled using LaGrangian approach. The reaction was modeled using non –premixed combustion which considers the effects of turbulence and detailed chemical mechanism into account to model the reaction rates. The specific heats for all the species was approximated by using piecewise polynomials. The fuel system consisted of an electronically controlled, common rail injection system with an injection pressure of 160 M Pa. 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 M Pa, 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 were 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.
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