A computational investigation of hydrotreated vegetable oil sprays using RANS and a modified version of the RNG k - ε model in openFOAM

Hydrotreated vegetable oil (HVO) is a high-cetane number alternative fuel with the potential of drastic emissions reductions in high-pressure diesel engines. In this study the behavior of HVO sprays is investigated computationally and compared with conventional diesel fuel sprays. The simulations are performed with a modified version of the C++ open source code OpenFOAM using Reynolds-averaged conservation equations for mass, species, momentum and energy. The turbulence has been modeled with a modified version of the RNG k-ε model. In particular, the turbulence interaction between the droplets and the gas has been accounted for by introducing appropriate source terms in the turbulence model equations. The spray simulations reflect the setup of the constant-volume combustion cell from which the experimental data were obtained. Simulations of non-evaporating and evaporating sprays have been performed for four different fuels, namely the diesel fuel DF2, n-heptane, the European-normed EN 590 fuel and the HVO fuel. These fuels have been compared with appropriate experimental data. The evaluation criteria include the liquid and vapor penetrations, the drop Sauter mean diameter (SMD) and the fuel vapor/air mixing. The agreement between the simulations and the experiments is generally acceptable in all cases, and it can be concluded that the spray models are sufficiently universal to make correct predictions for the alternative fuel HVO without any special adjustments.