A Computational Investigation of Flash-Boiling Multi-hole Injectors with Gasoline-Ethanol Blends

Gasoline-direct injection using multi-hole nozzles is prone to flash-boiling due to the transfer of thermal energy to the fuel combined with the sub-atmospheric pressures present in the cylinder during injection. Flash boiling is governed by a finite rate interphase heat-transfer mechanism and hence a thermal non-equilibrium model was used for simulations. Additionally, the fuel composition plays an important role in flash boiling and hence, any modeling of this phenomena must account for the type of fuel being used. In the current work, in addition to single component fuels, a non-ideal mixing model is used to calculate the properties of gasoline-ethanol blends. The flash boiling of the different single and multi-component fuels is compared and a parametric study is conducted to observe the importance of flash boiling. The purpose of this study is to use CFD calculations to propose dimensionless parameters that can help to understand how multiple time scales interact. In addition, we study the two-phase flow in a six-hole injector nozzle using E60 and E85 fuels. The results show that E60 generates more vapor and produces a wider spray cone angle. A previously unexplored phenomenon of string flash boiling is observed inside the nozzle and is found.