Decomposition of monopropellant blends of hydroxylammonium nitrate and imidazole-based ionic liquid fuels

Potential dual-mode monopropellant/electrospray-capable mixtures of hydroxylammonium nitrate with ionic liquid fuels [Bmim][NO₃] and [Emim][EtSO₄] are synthesized and tested for catalytic decomposition in a microreactor setup. The setup is benchmarked using a 30% hydrogen peroxide solution decomposed via silver catalyst. Results show similar trends but with variance in the quantitative data obtained in the literature. This was found to be a direct result of the sample-holder geometry. Hydrazine decomposition was conducted on an unsupported iridium catalyst. The same trends in terms of pressure-rise rate during decomposition (̃160 mbar/s) are obtained with unsupported catalyst but at 100 °C instead of room temperature for tests conducted on supported catalysts in the literature. For the [Bmim][NO ₃]/hydroxylammonium nitrate propellant, rhenium catalyst preheated to 160 °C yielded a pressure-rise rate of 26 mbar/s, compared to 14 mbar/s for iridium catalyst and 12 mbar/s for no catalyst at the same temperature. [Emim][EtSO₄]/hydroxylammonium nitrate propellant shows slightly less activity at 160 °C preheat temperature, yielding a pressure-rise rate of 20, 4, and 2.5 mbar/s for injection onto rhenium, iridium, and the thermal plate, respectively. Final results indicate that desirable ignition performance may potentially be obtained by using a supported rhenium catalyst.