Ionic liquid-H2O2 propellants and their ignition behavior

Abstract As the primary power source, propellants enable faster and more distant space exploration. While the traditional hydrazine-based bipropellants are gradually replaced due to their extreme volatility and carcinogenicity, ionic liquid-H 2 O 2 has become an important research direction for green propellants because of the environmental friendliness. This review mainly focuses on two aspects of ionic liquid-H 2 O 2 bipropellants: (1) the structures and properties of ionic liquids that spontaneously ignite with H 2 O 2 . These ionic liquids include the BH 3 CN − , BH 4 − , and SCN − -based compounds, which possess strong reduction ability, enabling hypergolicity with high-concentration H 2 O 2 ; (2) the structures and properties of catalysts that enhance the ignition of ionic liquids with H 2 O 2 . These catalysts include pure iodine-based, CuI-based, and metal (Cu, Ni, Mn) complex-based catalysts, which boost N(CN) 2 − -based ionic liquids from non-ignition to ignition, and BH-based ionic liquids from long to short ignition delay times with high-concentration H 2 O 2 . The properties of the mentioned ionic liquids and catalysts, such as decomposition temperature, density, viscosity, enthalpy of formation, and specific impulse, are analyzed. Ignition delay times are measured using drop tests, and imidazolium thiocyanate (IL 8 ) exhibits the shortest ignition delay time of 7.3 ms with 97% H 2 O 2 . Based on the calculations, N -methyl- N -ethylpyrrolidinium thiocyanate (IL 16 ) has the highest propulsion performance with a specific impulse of 320 s. Here, the detailed research of the ionic liquid-H 2 O 2 system is summarized, which is valuable to get the overall understanding and the new development of green propellants for rocket applications.