Droplet evaporation of alcohol-biodiesel blends

Abstract

Despite recent research on blends of biodiesel with higher alcohols in Diesel engines, no information on their behaviour as single droplets is available. This work presents experimental data on the droplet evaporation of blends of biodiesel with 1-propanol and 1-pentanol and compares them to the results of numerical models of droplet evaporation. The phase equilibrium of the non-ideal mixture of alcohol with biodiesel was modelled using activity coefficients calculated from the UNIFAC method, which was shown to accurately reproduce experimental VLE data from the literature. Droplet evaporation experiments were performed for 1-propanol/biodiesel and 1-pentanol/biodiesel blends at temperatures of 450 °C and 700 °C. The numerical modelling compared two different liquid phase models: well-mixed and diffusion-limited. The diffusion-limited model was found to best represent the droplet evaporation process, particularly early in the droplet lifetime. Internal boiling and bubble formation were observed for all mixtures, driven by the large difference in boiling point between the alcohol and biodiesel components (around 200˚C). The diffusion-limited model was also able to roughly predict the conditions under which bubble formation could occur.