Detailed Microscopic Reaction Mechanism during the Combustion Process of HAN-Based Propellant

Hydroxylamine nitrate (HAN)-based propellants, renowned for their high energy efficiency and nontoxic properties, are considered candidates for next-generation green propellants. The ab initio molecular dynamics (AIMD) method was used to theoretically study the thermal decomposition reaction process of the HAN aqueous solution and the system mixed by HAN and fuel methanol/ethylammonium nitrate. The principal reaction pathways of HAN-based propellants are delineated by scrutinizing AIMD trajectory results. HAN-based propellants transition from an ionic state to a neutral state during combustion, and the thermal decomposition of HAN begins with the breakdown of HNO₃ itself into ·NO₂ radicals and ·OH radicals. Although the thermal decomposition reaction of HAN is complex and a large number of intermediates are produced, only a few key free radicals and small molecules drive the subsequent reaction forward. The thermal decomposition of the fuel lags behind that of HAN in the combustion process of HAN-based propellants. The oxidants such as ·NO₂ produced by HAN decomposition react with fuel molecules, and the free radicals produced by the decomposition of oxidative products such as HONO further act as oxidants to react with fuel molecules again.