On the disruptive burning of free droplets of alcohol/n-paraffin solutions and emulsions

Abstract

A systematic experimental study of the low Reynolds number, atmospheric pressure combustion of free droplets of binary n-propanol/n-paraffin solutions and ethanol/n-paraffin solutions and emulsions was performed. Special attention was given to characterizing the disruptive burning phenomena for these fuel systems. The onset of disruptive burning was shown to be a function of both the difference between the normal boiling points and relative concentration of the solution components. Disruptive burning was found to be the result of homogeneous bubble nucleation within the interior of the droplet followed by the expansion and bursting of the gaseous nucleus. All ethanol/n-paraffin emulsions studied exhibited disruptive combustion behavior typical of solutions. This was attributed to dissolution of the dispersed phase during the transient heating period. In addition, similar disruptive behavior was demonstrated for solutions of ethanol in diesel fuel within the concentration range typical of that considered in fuel substitution applications. A simplified theory is proposed to predict the minimum concentration of alcohol required to produce the disruptive burning.