Investigation of Combustion Performance of Hypergolic Ionic Liquid Fuels Through Injector Design

Hypergolic ionic liquid fuels are promising alternatives to the toxic hydrazine-based propellants. The present study investigates the combustion performance of a fuel composed of 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) and copper(I) thiocyanate (CuSCN) with 95 wt% hydrogen peroxide (H2O2) in a 50 N thruster. Two injectors, DM1 (low pressure drop) and DM2 (high pressure drop), were tested at chamber pressures of 10 and 15 bar. The DM1 injector at 15 bar chamber pressure showed high combustion efficiency but suffered from strong pressure oscillations (>10% instability). Switching to the DM2 injector reduced instability (<5%) by increasing the pressure drop. Combustion stability was also improved as the fuel injector orifice diameter/fuel jet velocity (D/V) decreased. FFT analysis showed an instability frequency of 253 Hz with DM1/15 bar, which was higher than the DM1/10 bar test results. In conclusion, the test results revealed the injector or chamber design and pressure drop are the key factors in improving combustion stability for hypergolic propulsion systems.