Spray Entrainment Coefficient Modeling for High Injection Pressure Based on Entrainment Velocity and Force Analysis

Abstract

The entrainment coefficient reflects the air–fuel mixing quality, which is one of the foremost concerns for the development of cleaner and higher power-density internal combustion engines. Previous prediction models constructed by the change of axial mass flow rate have lower accuracy under high injection pressure conditions. During modeling in the work, a new construction method based on local entrainment velocity and local entrainment area is developed, and the influences of dilution effect and forces such as flow resistance, lateral pressure, etc. on the local entrainment velocity are considered. With the modified model, its prediction accuracy can be effectively extended to high injection pressure and detailed information about entrainment can be provided for analysis. It is found that, with the increase of injection pressure, the entrainment coefficient rises in the whole flow field. When increasing to high injection pressure, the entrainment coefficient constantly decreases with distance in the far-field, which is consistent with the experiments, but not a constant value predicted by previous models. Besides, the decreased rate of entrainment coefficient rises with the increase of injection pressure. Meanwhile, the increase of ambient pressure also makes the entrainment coefficient rise, but barely influences the decreased rate in the far-field. The large decrease of local entrainment velocity in the far-field caused by strong shear stress and flow resistance can explain the decrease of entrainment coefficient with distance. Overall, the modified model is able to rapidly predict the spray mixing quality over a wider range of operational conditions and provide more detailed entrainment information for analysis.