Additive-promoted hypergolic ignition of ionic liquid with hydrogen peroxide

Abstract

The exploration of environmentally friendly hypergolic combinations of ionic liquid fuels and hydrogen peroxide as an oxidizer offers opportunities to replace commonly used conventional toxic, corrosive and carcinogenic hydrazine-based liquid hypergolic combinations. Various research opportunities await regarding the detailed investigations of green hypergolic ionic liquids (HILs) with rocket grade hydrogen peroxide (RGHP, >85% H2O2). In this work, the combustion of HILs 1-ethyl-3-methyl imidazolium cyanoborohydride ([EMIM][BH3CN]) and 1-allyl-3-ethyl imidazolium cyanoborohydride ([AEIM][BH3CN]), and HIL-additive mixtures with 95% H2O2 has been investigated. A new additive, 1,3-dimethyl imidazolium copper iodide ([diMIM]n[Cu2I3]n) was synthesized successfully; a structural investigation was performed through the use of single-crystal x-ray diffraction analysis through which a crystal density of 3.22 g/cm3 was revealed. The physicochemical properties (density, viscosity, and decomposition temperature) as well as performance parameters (ignition delay and specific impulse) of 2 to 15 wt% of [diMIM]n[Cu2I3]n in [EMIM][BH3CN] were determined. A 15 wt% of [diMIM]n[Cu2I3]n exhibited ignition delay time (IDT) values of 13 and 29 ms under fuel-rich and oxidizer-rich conditions, respectively; these IDT values are 100 times lower than those for [EMIM][BH3CN]. Interestingly, [diMIM]n[Cu2I3]n-[EMIM][BH3CN] combinations revealed high density (>0.98 g/cm3), good thermal (>200 °C) and chemical stability, and 5.6–6.0% higher density specific impulse than those found for unsymmetrical dimethyl hydrazine. The additive-promoted hypergolic combustion of HIL with RGHP opens a new avenue to the replacement of conventional toxic hypergolic combinations.