Characterizing Hypergolic Propellants Using Impinging Jets and Droplets in Acoustic Levitation

This study presents an experimental investigation into the hypergolic ignition process of nontoxic propellants. Multispectral high-speed imaging was employed to capture the dynamic combustion process and temperature history across three distinct ignition setups. Six fuel samples containing different proportions of [Formula: see text]-tetramethylethylenediamine (TMEDA) and [Formula: see text]-methyldiethanolamine (MDEA), catalyzed with 1–2 wt% copper nitrate trihydrate (referred to as PAHyp 1), paired with rocket-grade hydrogen peroxide (RGHP) as the oxidizer, were selected. Formulations with higher concentrations of TMEDA containing 2 wt% catalyst paired with 95 wt% RGHP yielded ultrafast ignition delays as short as 7.6 ms in drop tests. Additionally, as binary droplet collision is a common occurrence in spray combustion, an acoustic levitator was proposed to study the ignition behaviors of droplet–droplet collision. The collision of binary droplets in the levitator, conducted at lower impact velocities, resulted in a minimum ignition delay time of about 17 ms. It was observed that depending on the size of the droplets and collision angle, ignition may not occur. This new approach to studying the dynamics of hypergolic ignition without “wall effects” has shown promise due to its ease of implementation. Finally, two fuel samples were selected to conduct ignition tests under flow conditions with an impinging jet apparatus. Remarkably, it was demonstrated that the addition of only 1 wt% is sufficient to achieve fast ignition with 90% hydrogen peroxide. Results from this new recipe indicate that samples containing at least 50% MDEA remain chemically stable for over 1 year and demonstrate competitive ignition and thermodynamic performance compared to conventional hydrazine-based fuels.