Theoretical performance evaluation of hypergolic ionic liquid fuels with storable oxidizers

Abstract

Hypergolic ionic liquids (HILs) have gained significant importance in recent years as green space propellants. It is mainly due to their attractive physicochemical properties, such as high density, negligible vapor pressure and wide liquid range. More importantly, they show low ignition delay with storable oxidizers viz. white fuming nitric acid (WFNA), red fuming nitric acid (RFNA), dinitrogen tetroxide (N₂O₄) and hydrogen peroxide (H₂O₂). Therefore, investigation into the performance parameters of HILs, such as specific impulse (I_sp), density and vacuum-specific impulse (ρI_sp & I_vac), and characteristics velocity (C*), has received enormous attention. In the present study, 14 HILs have been selected for evaluation of their performance parameters using the NASA-CEC-71 program. Amongst them, three HILs have been developed in the laboratory by the authors. The effects of oxidizers, oxidizer to fuel ratio, heat of formation, hydrogen content of the HIL, and the chamber pressure parameters were studied in detail. The performance of HILs was also compared with that of a proven fuel, UDMH. The HILs 1-ethyl-3-methyl imidazolium cyanoborohydride, [EMIM][BH₃CN], and 1,3-diallyl imidazolium cyanoborohydride, [diAIM][BH₃CN], were particularly promising with all the oxidizers. The H₂O₂ seems to be a good potential oxidizer as it exhibited a higher value of ρI_sp for most of the HILs than the UDMH. A propellant based on high-density HIL as a fuel and H₂O₂ as an oxidizer can be classified as a green propellant. Thus, the investigation helps in designing or selecting the best combination of HIL and oxidizer for rocket applications.