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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.

When developing new combustion concepts, CFD simulations is a powerful tool. The modeling of spray formation is a challenging but important part when it comes to CFD modelling of non-premixed combustion. There is a large difference in the accuracy and robustness among different spray models and their implementation in different CFD codes. In the work presented in this paper a spray model, designated as VSB2 has been implemented in OpenFOAM. VSB2 differ from traditional spray models by replacing the Lagrangian parcels with stochastic blobs. The stochastic blobs consists of a droplet size distribution rather than equal sized droplets, as is the case with the traditional parcel. The VSB2 model has previously been thoroughly validated for spray formation and combustion of n-heptane. The aim of this study was to validate the VSB2 spray model for ethanol spray formation and combustion as a step in modelling dual-fuel combustion with alcohol and diesel.

The accuracy and robustness of spray models and their implementation in current commercial CFD codes vary substantially. However, common features are that the resulting spray penetration and levels of spray-generated turbulence - two factors that strongly influence the rate of heat released during combustion - are to a great extent grid size-dependent. In the work presented here a new kind of spray model has been implemented and thoroughly tested, under various ambient conditions, in the open source code OpenFOAM. In addition, since the turbulence model applied in simulations is known to strongly affect spray penetration rates, results obtained using both the standard k-ε and RNG k-ε models have been compared. In the new spray model, designated VSB2, the traditional Lagrangian parcel has been replaced by a so-called stochastic blob containing droplets with a distribution of sizes, rather than a number of uniform-sized droplets.