To enable the practical implementation of electrical ignition systems for spacecraft thrusters using an energetic ionic liquid, understanding the relationship between the composition, propellant performance, and electrochemical properties is important. The objective of this study is to investigate the effect of composition on propellant properties (e.g., theoretical specific impulse, solid precipitation at -35℃) and electrochemical properties (e.g., electrolysis onset potential and specific resistivity) in a binary mixture of ammonium dinitramide and 2-hydroxylethylhydrazinium nitrate (ADN/HEHN). The theoretical specific impulse for ADN/HEHN mixtures increased with increasing ADN content, reaching a maximum of 298 s at an ADN molar ratio of 62%. A freezing test at -35℃ revealed that no solid precipitation occurred at ADN molar ratios of 50% or lower. Linear sweep voltammetry measurements showed that the electrolysis onset potential for the anode was 1.5±0.3 V vs. Ag, whereas the electrolysis onset potential for the cathode was -1.0 V vs. Ag for pure HEHN and -0.4 V vs. Ag for compositions containing ADN. Electrochemical impedance spectroscopy measurements showed that the specific resistivity decreased with increasing ADN molar ratio, reaching approximately one-third of the value for pure HEHN (611 Ω･cm) at an ADN molar ratio of 60% (195 Ω･cm). Among the compositions without solid precipitation at -35℃, the ADN/HEHN

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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.

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