Early Liquid and Gas Phase Hypergolic Reactions between Monomethylhydrazine and Nitrogen Tetroxide or Red Fuming Nitric Acid

Monomethylhydrazine (MMH) fuel and nitrogen tetroxide (NTO)-based oxidizers embody the state of the art for hypergolic propellants. Despite their wide use, a detailed understanding of the full reaction chemistry between MMH and NTO, from early liquid phase reactions to ignition in the gas phase, is lacking. The gas phase reactions are relatively well understood with several spectroscopic techniques well suited to probe gaseous reaction zones and numerous computational chemistry studies supporting the experimental data. The present paper focuses on the early liquid phase reactions with a method devoted to the determination of Arrhenius preexponential factors and activation energies for global, single-step liquid phase chemical reaction models for MMH-NTO and MMH-red fuming nitric acid (RFNA) systems. Using a temperature and atmosphere controlled droplet contact chamber, the liquid phase induction delay times of MMH-RFNA and MMH-NTO were examined by capturing drop on drop tests at frame rates from 100,000 to 500,000 fps. Results indicate induction delays on the order of 30-100 microseconds and 10-40 microseconds for MMH-RFNA and MMH-NTO, respectively, and distinct reaction rate parameters for both pairs of propellants.