Trialkylsulfonium Thiocyanate Ionic Liquids: Investigation on Temperature-Dependent Ignition Behavior of Green Hypergolic Propellants

Abstract

Three trialkylsulfonium thiocyanate ionic liquids (ILs) are presented as fuel candidates for novel green hypergolic propellants. The physical and chemical properties such as density, viscosity, melting point and decomposition temperature as well as the enthalpy of formation of the ILs were determined. Further, the research focused on the potential of the ILs as fuel components for hypergolic propellants with highly concentrated hydrogen peroxide as oxidizer. For this, the theoretical maximum specific impulses of the propellants were calculated with NASA CEA. To evaluate the ignition delay times of the hypergolic propellants, drop tests were carried out. These were conducted not only at ambient conditions but also at lower levels of fuel temperature. It was found that all three propellant combinations still ignited reliably at temperature levels down to -25 °C, however, the average ignition delay increased at lower temperatures. Overall, not only three promising hypergolic fuels were identified, but also important insights into the temperature-dependent ignition behavior of hypergolic ionic liquid-based propellants with thiocyanate anions were obtained.