A reduced quasi—dimensional model to predict the effect of nozzle geometry on diesel engine performance and emissions

Abstract

The predictive capability of the engine cycle simulation previously developed on the basis of a reduced quasi—dimensional combustion model has been enhanced by introducing a new submodel that correlates the discharge coefficient of the injector nozzle with the design variables of the nozzle and injection conditions. This enhancement enables prediction of the effect of microvariations in the injector nozzle hole geometry as well as the variations in the main design parameters on diesel spray evolution and combustion processes. As a result, the engine cycle simulation model can predict changes in engine performance and emissions due to injector nozzle design changes. First, the effect of the chamfer radius of the injector nozzle inlet on the discharge coefficient at various injection pressures was explored by simulating fuel injection in a constant—pressure vessel. The results showed that a larger chamfer radius improves the discharge coefficient and the rounded nozzle inlet can also reduce injector—to—injector variation. A case study of the injector nozzle hole design optimization was also performed for several different objectives to demonstrate the usage of the engine cycle simulation as a simulation tool. The case study showed that an optimized injector hole diameter depends on the objective while a larger chamfer radius, in general, helps to improve both engine performance and emissions.