Experimental Validation of a Droplet Vaporization Model for Ethanol-Blended Fuels and its Application to Spray Simulation

Ethanol is a promising alternative to fossil fuels because it can be made from biomass resources that are renewable. In the most cases, however, ethanol is blended with conventional fuels because of the limited amount of production. Ethanol-fuel blends are typically azeotropic and have a unique characteristic in vapor pressure and phase equilibrium, which is different from that of blends composed of simple aliphatic hydrocarbons. The current studies by the authors have developed a numerical vaporization model for ethanol-gasoline blends, which takes into account vapor-liquid equilibrium of azeotrope and high latent heat of vaporization of ethanol, in order to update the authors' multicomponent fuel spray model and to investigate effects of blending ethanol on droplet vaporization processes. In this paper, the developed vaporization model was validated through a comparison with experimentally-observed vaporization rate for single droplets of ethanol-n-heptane blends. The predicted results were in a good agreement with experimental data. The results also showed that the latent heat of vaporization of ethanol plays an important role in a droplet vaporization rate while the increase of the vapor pressure due to mixing ethanol has less effect and that consideration of the phase equilibrium composition is required to correctly predict the temporal change of the composition in a vaporizing droplet. Finally, the developed vaporization model was incorporated into authors' multicomponent fuel spray model. The effects of liquid-vapor equilibrium of ethanol-n-heptane blends and the latent heat of vaporization of ethanol were evaluated for vaporizing fuel spray.