Biphasic Dispersion Fuels for High-Regression-Rate Hybrid Rockets

Abstract

Biphasic dispersion fuels (BDFs) are multiphase mixtures in which liquid droplets are trapped in a solid binder to form stable hybrid propellant grains. As the flame transfers heat to the fuel grain surface, the internal pressure of the liquid droplets rises, leading to microexplosions that force small droplets and fuel vapors into the flame zone. The combined effects of the liquid fuel being dispersed in the combustion chamber and the craters formed by surface-level microexplosions should lead to high combustion efficiencies and high regression rates. As an initial step in developing BDF, nonionic surfactants and a high shear homogenizing unit were used to emulsify water and ethanol in paraffin wax. The mixtures were cooled and casted into cylindrical fuel grains, and their performance was evaluated with gaseous oxygen in an optically accessible hybrid rocket motor. Results indicate that both BDF formulations exhibited increased regression rates, relative to neat paraffin wax, at all oxidizer mass fluxes tested. The water-based fuels demonstrated up to a 32% increase in regression rate and a 1% increase in average combustion efficiency, relative to neat paraffin fuels. The ethanol-based fuels demonstrated up to a 95% increase in regression rate and a 4% decrease in average combustion efficiency, relative to neat paraffin fuels.