A Computational Study of Flashing Flow in Fuel Injector Nozzles

Flash boiling conditions, where the fuel is superheated with respect to cylinder pressure, are often found in gasoline direct injection engines. This phenomenon affects the flowrate of the fuel and can cause choking of the nozzle. In this work we present multi-dimensional simulations of flashing internal injector flow. The modeled fluid quality ( mass fraction of vapor) tends towards the equilibrium quality based on the Homogenous Relaxation Model. The relaxation time is dependent on the local pressure, the vapor pressure, and the void fraction. Simulations of the internal flow are presented and, where possible, validated with experimental data. Both two- and three-dimensional computational results show geometrically-induced phase change, similar to cavitation, near the nozzle entrance. Near the nozzle exit plane the phase change occurs at all radial locations and can be quite sensitive to temperature. Three-dimensional simulations run in an asymmetric injector tip at higher injection pressure show reduced sensitivity to temperature.