Rapid ignition of "green" bipropellants enlisting hypergolic copper (II) promoter-in-fuel.

[Display omitted] • Hypergolic energetic copper complexes are investigated as new promoters. • Low ignition delay of "green" fuels with 70% and 95% hydrogen peroxide. • Promoter lowers the ignition delay of ionic liquids by 1000 times. • Non-hypergolic to hypergolic fuels by using promoter. Ionic liquid-with-promoter fuels and H 2 O 2 oxidizer require optimization and further exploration of inexpensive initiators that can be understood at the molecular level; it is advantageous when exacting structural characterization comparisons can also be made. For the first time, hypergolic energetic copper(II) complexes viz. [CuII(1-H-imidazole) 4 (BH 3 CN)][BH 3 CN] (Cu-P1) and [CuII(1-methyl imidazole) 4 (BH 3 CN) 2 (Cu-P2) were developed as new 'promoters' for "green" space vehicle propulsion. Cu-P1 and Cu-P2 exhibited ignition delay times (IDTs) of 3.75 and 8.5 ms, respectively, with 95% H 2 O 2. The superior solubility of Cu-P1 in ionic and non-ionic fuels helped to promote the hypergolic ignition of green liquid fuels. The ionic liquid, 1-ethyl-3-methyl imidazolium cyanoborohydride ([EMIM][BH 3 CN]), non-ionic tetraglyme, and mixtures thereof (1:1, wt/wt%) were employed. A 13 wt% of Cu-P1 in [EMIM][BH 3 CN] improved the IDT from >1000 ms to 9.50 ms with 95% H 2 O 2 and from >5000 ms to 21.25 ms with 70% H 2 O 2. Hence, the development of a suitable energetic promoter, soluble in ionic liquid, gained significant attention for "green" bipropellant development. Interestingly, tetraglyme is non-hypergolic with H 2 O 2 ; a 13 wt% Cu-P1 induced the hypergolic ignition with an IDT of 9.0 ms (95% H 2 O 2). Moreover, the fuel mixture of [EMIM][BH 3 CN] and tetraglyme (1:1, wt/wt%) with 13 wt% Cu-P1 also revealed the shortest IDT of 7.75 ms (95% H 2 O 2) and 16.5 ms (70% H 2 O 2). The superior ignition performance, reasonable viscosity and density, long-term stability of promoter in the fuel, and comparable theoretical performance of hypergolic propellants are advantages of our approach. [ABSTRACT FROM AUTHOR]