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

Hydroxylamine nitrate (HAN)-based\npropellants, renowned for their\nhigh energy efficiency and nontoxic properties, are considered candidates\nfor next-generation green propellants. The <i>ab initio</i> molecular dynamics (AIMD) method was used to theoretically study\nthe thermal decomposition reaction process of the HAN aqueous solution\nand the system mixed by HAN and fuel methanol/ethylammonium nitrate.\nThe principal reaction pathways of HAN-based propellants are delineated\nby scrutinizing AIMD trajectory results. HAN-based propellants transition\nfrom an ionic state to a neutral state during combustion, and the\nthermal decomposition of HAN begins with the breakdown of HNO<sub>3</sub> itself into ·NO<sub>2</sub> radicals and ·OH radicals.\nAlthough the thermal decomposition reaction of HAN is complex and\na large number of intermediates are produced, only a few key free\nradicals and small molecules drive the subsequent reaction forward.\nThe thermal decomposition of the fuel lags behind that of HAN in the\ncombustion process of HAN-based propellants. The oxidants such as\n·NO<sub>2</sub> produced by HAN decomposition react with fuel\nmolecules, and the free radicals produced by the decomposition of\noxidative products such as HONO further act as oxidants to react with\nfuel molecules again.