Development and Validation of a Multicomponent Fuel Spray Model (VSB2 Model)

Owing to increased interest in blended fuels for automotive applications, a great deal of understanding is sought for the behavior of multicomponent fuel sprays. This sets a new requirement on spray model since the volatility of the fuel components in a blend can vary substantially. It calls for careful solution to implement the differential evaporation process concerning thermodynamic equilibrium while maintaining a robust solution. This work presents the Volvo Stochastic Blob and Bubble (VSB2) spray model for multicomponent fuels. A direct numerical method is used to calculate the evaporation of multicomponent fuel droplets. The multicomponent fuel model is implemented into OpenFoam CFD code and the case simulated is a constant volume combustion vessel. The CFD code is used to calculate liquid penetration length for surrogate diesel (n-dodecane)-gasoline (iso-octane) blend and the result is compared with experimental data. The liquid penetration length predictions follow the trend of the experiment. There is a decrease in the liquid penetration with increase in proportion of iso-octane (surrogate gasoline) as observed in the experiments. The CFD code is also applied to calculate vapor fraction of individual components in the fuel. A shift in peak of vapor fraction is observed for the two components with respect to the distance from injector. The more volatile component has an earlier peak in vapor fraction. Temperature dependence of differential evaporation is studied with respect to the influence on liquid penetration. It is seen that at higher temperatures, the differential evaporation effect is reduced. The evaporation rate of single component surrogate fuel spray is calculated and compared with that of multicomponent fuel spray. The model captures the difference in evaporation rates.