Characterization of a novel ionic liquid monopropellant for multi-mode propulsion

A deep eutectic 1:2 molar ratio mixture of choline-nitrate and glycerol [Cho][NO₃] - glycerol is investigated as a fuel component in a binary mixture propellant for multi-mode micropropulsion. Specifically, binary mixtures of the novel ionic liquid fuel with hydroxyl-ammonium nitrate (HAN) and ammonium nitrate (AN) are considered and compared against our previously investigated propellant [Emim][EtSO₄]-HAN. Chemical rocket performance simulations predict this new propellant to have higher performance (280 vs. 250 sec specific impulse) at lower combustion temperature (1300 vs. 1900K), relaxing catalyst melting temperature requirements and making it a promising alternative. Qualitative experimental investigation of synthesized propellants on a hot plate in atmosphere indicate the AN mixtures are significantly less reactive, and are therefore not investigated further. Quantitative reactivity studies using a microreactor indicate that both 65:35% and 80:20% by mass [Cho][NO₃] - glycerol to HAN propellants have a decomposition temperature 26-88% higher than [Emim][EtSO₄]-HAN, depending on the catalyst material. Additionally, the decomposition rate (or self-heating rate) was 2 to 17 times slower for [Cho][NO₃] - glycerol - HAN on titanium and platinum catalysts, but the 65:35% propellant decomposition rate was approximately 10 °C/s (37%) faster on rhenium. It was also observed that propellants with the novel ionic liquid fuel contain endothermic reaction steps, and therefore higher input heat flux was required to maintain a temperature rise. Overall the results indicate [Emim][EtSO₄]-HAN with platinum catalyst is still most promising as a multi-mode micropropulsion propellant.