Utilizing preferential vaporization to enhance the stability of spray combustion for high water content fuels

Abstract

In a previous study on the stability of spray combustion for mixtures of alcohols (ethanol or 1-propanol) and water, the feasibility of burning fuels heavily diluted with water was demonstrated. In that study it was found that the preferential vaporization of alcohols in water can significantly enhance flame stability. Due to their high volatility and high activity coefficient in aqueous solution, the alcohols quickly evaporate from the droplets and generate a concentrated fuel vapor at the base of the jet. Therefore, a flame can be ignited and stabilize even though the water content of the fuel is quite high (up to 90wt%) (Yi and Axelbaum, 2013). In this study, we develop a procedure for selecting chemical fuels showing strong preferential vaporization in water. t-Butanol was identified as an excellent candidate based on its physical and chemical properties, including activity coefficient, vapor pressure, heat of vaporization and heat of combustion. Flame stability was evaluated for aqueous solutions of both ethanol and t-butanol using a spray burner where the extent of swirl was adjustable. Under both high and low swirl intensity, the flame stability of t-butanol aqueous solutions was better than that of ethanol. The characteristic time for fuel release from a droplet was modeled for both ethanol and t-butanol. The time to release 99% of the fuel from the droplet for t-butanol is over 70% shorter compared to that for ethanol, which supports the improved flame stability observed for t-butanol in the experiments.