Modelling of evaporative losses in n-alcohol/diesel fuel blends

Alcohol/diesel fuel blends allow reducing the formation of soot in diesel engines. However, its use in a large scale framework still faces the challenge of high evaporative losses under storage conditions which is hindered by the high volatility of the alcohols. Since the design of the most adequate fuelling system for each blend requires detailed knowledge about the evaporation losses from the liquid phase, in this work a method for calculating the evaporation of pure n-alcohols (from C1 to C5 carbon atoms) and blends of these alcohols with ultra-low sulphur diesel (ULSD) was proposed. Alcohols vapour pressure was determined with the Antoine equation, while the diffusion coefficient of alcohols in air was calculated as a function of carbon number and temperature. The coefficients of activity were obtained by the combination of continuous thermodynamic (gamma distribution function) and a modified UNIFAC-Dortmund-Continuous method. The evaporation losses model is based on Fick's law and exhibited good agreement with experimental data for all alcohols and blends at 20% content of all alcohols and at 20-60% contents of n-butanol with diesel fuel. The evaporation was found to decrease approximately with an inversely proportional rate with respect to the increase in the carbon chain length of the alcohol. The paradox of faster evaporative losses from blends with lower alcohol content is explained.