Abstract
Hybrid rocket engines are rarely used in practice because they have low regression rates. Therefore, attempts to increase regression rates have included augmentation of solid fuels with additives having high heat of combustion. This
study specifically evaluated the performance of solid fuels with additives and assessed the combustion completeness of those additives: specifically boron, Al, and Mg powders. Boron powder has high combustion heat but its particles have an
oxide shell that requires large amounts of heat to ignite. Actually, Al has the second highest heat of combustion after boron, but it also has an oxide shell and presents inherent ignition difficulties. Therefore, we introduced of magnalium
(Mg-Al), which has higher ignitability than that of Al alone. By virtue of this characteristic, Mg-Al powder was expected to be effective at increasing boron powder ignitability.
Two-dimensional (2D) visualization experiments demonstrated that the additives increased the regression rate, but the metal powder addition to the fuel beyond a certain percentage decreased the regression rate.
Combustion experiments using a hybrid rocket engine verified Mg and Al composition effects on the boron combustion completeness. Experimentally obtained results demonstrated that the characteristic velocity increased and that the fuel
regression rate decreased under conditions with boron and Al only. Because Al was a finer powder than the Mg powder used for this experiment, the liquefied fuel viscosity was expected to be greatest when it contained boron and Al only.
