Fundamental Research on Decomposition and Ignition of Monopropellants

Thermal and electrolytic decomposition and ignition of water solutions of hydroxylammonium nitrate (HAN, [NH3OH]+[NO3]-) are investigated. Experiments are conducted to demonstrate the feasibility of electrolytic ignition for HAN-based ionic liquid propellants. As a consequence of electrolysis, the propellant decomposes to NH2OH, HNO3, HONO, HNO, N2O, N2, NO, NO2, H2O, H2(g), and O2(g). These species then initiate a series of gas phase reactions, governed by the H-O-N kinetics scheme, and lead to ignition. Electrochemical mechanisms are established and incorporated into an existing chemical kinetics scheme for thermal decomposition of HAN-water solutions. The analysis treats the liquid and gas phases separately, and matches their respective processes at the interfacial boundary to determine the overall decomposition and ignition characteristics. Results are benchmarked against experimental data for the species evolution in the condensed phase, as well as laser-induced ignition delay of 13M HAN-water solution. The effects of electric current (0-2.5A), propellant volume (0.1-0.3cc), initial temperature (300-450K), and HAN concentration (9-13M) on the ignition behaviors are investigated systematically. The ignition delay decreases with increasing electric current as a power-law function: τ_ign = AI^-n, where A = 3.95 and n = 0.95 for a 0.1cc 13M HAN-water solution at an initial condition of 300K and 1atm. The exponent n and coefficient A are decreasing functions of the initial temperature. For a given power, decreasing the initial volume of HAN-water solution increases the current density available for electrolysis, and expedites the ignition process. The work represents the first theoretical study of its kind on this topic.

1. P. Khare, V. Yang, H. Meng, G.A. Risha, R.A.Yetter, (2015) "Thermal and Electrolytic Decomposition and Ignition of HAN-water Solutions",
   Combustion Science & Technology 187(7), 1065-1078.
2. H. Meng, P. Khare, G.A. Risha, R.A. Yetter, V. Yang, "Decomposition and ignition of HAN-based monopropellants by electrolysis",
   47th AIAA Aerospace Sciences Meeting and Exhibit, January 2009, Orlando, Florida.
3. Prashant Khare, Master of Science Thesis,
   Department of Mechanical Engineering, Pennsylvania State University, University Park, May 2009.