Ignition Delays of Mixtures of the Non‐Hypergolic Energetic Ionic Liquid Hydroxyethylhydrazinium Nitrate Blended with Unsymmetrical Dimethylhydrazine

Abstract

AbstractThe study deals with the investigation of energetic ionic liquids capable of serving as both monopropellants and bipropellants on a single mission. Various blends of the monopropellant hydroxyethylhydrazinium nitrate (HEHN), which was found to be non‐hypergolic with red fuming nitric acid (RFNA) and white fuming nitric acid (WFNA) under ambient conditions, were formulated with known hypergols to impart hypergolicity and to reduce the viscosity and surface tension of pure HEHN. Considering the miscibility and the ignition delays of the chosen hypergols, unsymmetrical dimethylhydrazine (UDMH) was chosen as the candidate for combustion characterization through measurement of ignition delays. UDMH‐HEHN blends containing a minimum of 30 % and 40 % UDMH by weight were found to be hypergolic with RFNA and WFNA, respectively. Meticulous experiments were conducted to measure the ignition delays in a drop test setup, equipped sequentially with a high‐speed camera, which was primarily utilized to observe the physico‐chemical events governing ignition, as well as an optoelectronic diagnostic setup, which was utilized to segregate the physical and chemical ignition delays. Standard hypergolic propellants were chosen to compare the veracity of the data from the optoelectronic diagnostics setup with those obtained using a high‐speed camera. The hypergolic blend containing 60 % UDMH was found to be the best candidate, owing to its low ignition delay of 5.8 ms with RFNA, 80 % lower vapor pressure compared to UDMH, and 30 g‐s/cm3 higher predicted vacuum density specific impulse than UDMH with IRFNA.