Thermal and Electrolytic Decomposition and Ignition of HAN–Water Solutions

Abstract

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 13 M HAN–water solution. The effects of electric current (0–2.5 A), propellant volume (0.1–0.3 cc), initial temperature (300–450 K), and HAN concentration (9–13 M) on the ignition behaviors are investigated systematically. The ignition delay decreases with increasing electric current as a power-law function: , where A = 3.95 and n = 0.95 for a 0.1 cc 13 M HAN–water solution at an initial condition of 300 K and 1 atm. 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.

Keywords:

• Electrolytic ignition
• Green propellants
• HAN
• Ignition
• Liquid monopropellants

Notes

¹ LD₅₀, a standard measure for expressing and comparing the toxicity of chemicals, is defined as the dose that kills half (50%) of the animals, e.g., rats or mice, tested. Common units are milligram of chemical per kilogram of the test animal (mg/kg).

Additional information

Funding

This work was sponsored in part by Air Force Office of Scientific Research, Grant Number FA9550-04-1-0291, and in part by the William R. T. Oakes endowment of the Georgia Institute of Technology.