Performance improvement of triglyme-based fuels using an ionic liquid with hydrogen peroxide

Low-toxicity hypergolic propellants have been a demanding research area in recent years for space propulsion, with the aim of replacing conventional toxic propellants. Therefore, the current research was focused on the development of low-toxicity hypergolic propellants for safe, cost-effective, and sustainable space exploration. In this study, triglyme was selected as a fuel component for the low-toxicity hypergolic propellant. Hypergolic performance of various concentrations (3 to 13 wt%) of monocyanotrihydroborate tetrakis(imidazole) copper(II) cyanotrihydroborate additive (Cu-P1) in triglyme fuel was experimentally investigated with 70, 90 and 95 wt% hydrogen peroxide (H₂O₂). The new fuels, 13Cu-TriG and 13Cu-TriGIL, containing 13 wt% of Cu-P1 in triglyme and triglyme:1-ethyl-3-methyl imidazolium cyanoborohydride ([EMIM][BH₃CN]) blend, respectively, were investigated. The hypergolic performance and properties of triglyme were improved by using [EMIM][BH₃CN]. For example, 13Cu-TriG was not ignited with 70 wt% H₂O₂; however, 13Cu-TriGIL exhibited an IDT of 16.5 ms. Furthermore, 13Cu-TriG and 13Cu-TriGIL revealed an IDT of 18.7 and 8.0 ms, respectively, with 95 wt% H₂O₂. The physicochemical properties, such as density, viscosity, decomposition temperature, and freezing/melting temperature, of 13Cu-TriG and 13Cu-TriGIL, were also measured. 13Cu-TriGIL showed a density of 1.017 g/cm³ and a viscosity of 26.42 mPa·s. Additionally, 13Cu-TriG exhibited a freezing point of −45 °C. However, with the addition of [EMIM][BH₃CN] in the fuel, the freezing temperature drops below −80 °C (13Cu-TriGIL). Furthermore, 13Cu-TriGIL with 95 wt% H₂O₂ demonstrated theoretical specific impulse and density specific impulse of 2.1 % lower and 9.7 % higher than MMH/NTO, respectively. Overall, the use of ionic liquid to improve the hypergolic performance and physicochemical properties of triglyme-based fuels was the advantage of our research.