Electronically Driven Combustion of Energetic Ionic Liquids in a Microcell Reactor

This study presents a microcell reactor platform designed to investigate the electronically driven combustion of energetic ionic liquids through nanosecond pulsed plasma discharges. A fuel mixture of 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIM]-[EtSO₄]) and hydroxylammonium nitrate (HAN) with this system enables controlled ignition and characterization of intermediate species formed during plasma-assisted decomposition. The high throughput testing provided by the microcell reactor also enables rapid testing of variations of fuels to investigate combustion enhancements from dopants such as carbon nanotubes. The approach also enables us to differentiate between the thermally driven and plasma-driven processes involved in the combustion of [EMIM]-[EtSO₄] and HAN through optical emission spectroscopy and Raman shift thermometry. This analysis allows for in situ diagnostics of reactive species and temperature evolution. Optical emission spectra reveal distinct reaction intermediates, including CN, C₂, N₂, and atomic H and N, and the mixture also exhibits broad spectral features indicative of exothermic combustion (i.e., continuum thermal radiation). Raman thermometry using a commercially available micro-Raman spectrometer, provides quantitative temperature measurements, enabling differentiation between thermally- and plasma-driven processes. The HAN+[EMIM]-[EtSO₄] solution exhibits a higher temperature-induced shift, due to the nanosecond high voltage pulse excitation, than what was observed during the measurement of the individual ionic liquids. The microcell's compact and reconfigurable design allows rapid assembly and testing of various oxidizer-fuel combinations. This offers a high-throughput approach for advancing green monopropellant research and understanding plasma-assisted reaction mechanisms.