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

Abstract

The 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.

Experimental and Theoretical Studies of HAN and HEHN Pyrolysis at Low Pressure

“…11−13 HEHN has been proposed as an additive to unsymmetrical dimethylhydrazine (UDMH) to improve fuel performance. 14 HEHN was also considered a suitable substitute for Otto fuel II monopropellant in propulsion systems. 15 HAN and HEHN propellants are chemically more reactive than hydrazine.…”

“…Among them, HAN is a high-energy ionic liquid. As a new rocket propellant with low toxicity, low boiling point, high density, and high energy pulse, − it is considered one of the most promising alternatives to hydrazine. − HEHN has been proposed as an additive to unsymmetrical dimethylhydrazine (UDMH) to improve fuel performance . HEHN was also considered a suitable substitute for Otto fuel II monopropellant in propulsion systems .…”

Different Ignition Modes and Temperature Evolution of Typical Hypergolic Ionic Liquids

“…and Europe . In recent years, many “green propellant” candidates (mainly fuels) have been reported, including ammonium dinitramide and hydroxylammonium nitrates (as monopropellant), hydrogen peroxide (H 2 O 2 ) , and nitrous oxide (N 2 O) (as oxidizer), blends of hydrocarbon fuel and ignition source (like NaBH 4 ), , and ionic liquid. − …”

Structural Properties of HEHN- and HAN-Based Ionic Liquid Mixtures: A Polarizable Molecular Dynamics Study

“…Previously studied EIL monopropellant formulations involve mixtures of common ionic oxidizers [e.g., hydrazinium nitrate (HN), − ammonium nitrate (AN), ammonium dinitramide (ADN), − hydroxylammonium nitrate (HAN), − etc.] with ionic fuels [e.g., ammonium azide (AA), 2-hydroxyethylhydrazinium nitrate (HEHN), etc. ], molecular fuels (e.g., methanol, ethanol, glycerol, etc.…”