Numerical Investigation of Droplet Evaporation in High-Pressure Dual-Fuel Conditions Using a Tabulated Real-Fluid Mode

Abstract : The substitution of diesel by cleaner renewable fuels such as short-chain alcohols in dual-fuel internal combustion engines is considered an attractive solution to reduce the pollutant emissions from internal combustion engines. In this context, two-phase flow models for multi-component mixtures considering the real-fluid thermodynamics are required for further understanding the evaporation and mixing processes in transcritical conditions. The present study proposes an efficient real-fluid model (RFM) based on a two-phase, fully compressible four-equation model under mechanical and thermal equilibrium assumptions with a diffused interface and closed by a thermodynamic equilibrium tabulation approach. Compared to previous research limited to binary mixtures tabulation, the proposed pre-tabulation approach can further handle ternary mixtures using a thermodynamic table that has been coupled to the CONVERGE CFD solver. The newly developed RFM model has been applied to investigate the evaporation of an n-dodecane droplet in a mixed ambient (methanol and nitrogen) relevant to dual-fuel configuration compared to pure nitrogen ambient. The four equation model is closed by a tabulated Cubic Plus Association (CPA) and Peng–Robinson (PR) equations of state for the droplet evaporation in a mixed and single component ambient, respectively. Numerical predictions show that the n-dodecane droplet lifetime decreases monotonically with increasing the methanol ambient concentration under the considered transcritical conditions. The performed thermodynamic analysis demonstrates that the droplet follows a different thermodynamic path as a function of the methanol ambient concentration. The different mechanisms contributing to the droplet lifetime behavior under varying ambient conditions are discussed.