Modeling ethanol–blended gasoline droplet evaporation using COSMO-RS theory and computation fluid dynamics

Abstract

A new single droplet evaporation model for ethanol–blended gasoline is presented. The real liquid mixture model based on the quantum chemical ab initio description of non-ideality of liquid phase without need of any adjustable parameters. The multi-scale model applies the COSMO-RS theory (micro level) for the estimation of vapor–liquid equilibrium of non-ideal solutions and the Maxwell–Stefan diffusion and convection theory for the calculation of gas phase transport (macro level) characteristics of the components. Solvation mixture thermodynamics and computational fluid dynamics (CFD) simulation were used to perform the calculations for the quasi-equilibrium evaporation of compounds from curved liquid surface. Physical–chemical properties, which are difficult to measure experimentally the activity coefficients of the components, the liquid and vapor phase compositions, the cumulative and components evaporation fluxes among others were computed during the evaporation process. A new approach for calculating the temperature-depression of evaporating droplets is also reported. The model was validated against experimental evaporation data of multi-component alcohol–alkane mixtures. The validated model was used to predict the impact of ethanol on volatilities of droplets of ethanol–blended model gasoline. The estimated non-linear trend in vapor pressures of ethanol–blended model gasoline is consistent with the experimentally observed effects of ethanol addition on dry vapor pressure equivalent values of gasoline base stock samples.