A Numerical Model for Flash Boiling of Gasoline-Ethanol Blends in Fuel Injector Nozzles

Fuels are formulated by a variety of different components characterized by chemical and physical properties spanning a wide range of values. Changing the ratio between the mixture component molar fractions, it is possible to fulfill different requirements. One of the main properties that can be strongly affected by mixture composition is the volatility that represents the fuel tendency to vaporize. For example, changing the mixture ratio between alcohols and hydrocarbons, it is possible to vary the mixture saturation pressure, therefore the fuel vaporization ratio during the injection process. This paper presents a 1D numerical model to simulate the superheated injection process of a gasoline-ethanol mixture through real nozzle geometries. In order to test the influence of the mixture properties on flash atomization and flash evaporation, the simulation is repeated for different mixtures characterized by different gasoline-ethanol ratio. The Homogeneous Relaxation Model (HRM) is used as non-equilibrium two-phase model. As equation of state, the Peng Robinson equation is considered. Non-ideal thermodynamic properties are considered for the gasoline-ethanol blends. About the gasoline, a binary surrogate is used. The thermodynamic saturation properties of the multi-component blends are calculated by using fugacity and standard mixing rules for the cubical equation of state. The proposed 1D model is validated against experimental data available in literature. The simulation results reveal as the azeotropic behavior of the mixtures characterized by a medium-low ethanol concentration affected the mixture superheating degree influencing the flash evaporation and effervescent atomization outside the nozzle exit. These results can be used to improve initial condition for 3D CFD Lagrangian spray simulations especially when the spray targeting plays a fundamental role as for the Gasoline Direct Injection (GDI) engine.