Molecular dynamics simulation of thermal decomposition mechanism for HAN based monopropellant
In order to reveal the decomposition mechanism of hydroxylamine nitrate(HAN)based monopropellant in non catalytic monopropellant liquid rocket engine,molecular dynamic simulation method based on ReaxFF/lg force field was used to study both thethermal decomposition mechanism and the influence of propellant formulation.The calculation results show that there are two stages in the thermal decomposition process of the propellant.The first stage is the endothermic stage,where the hydrogen bonds of hydroxylamine nitrate and hydrazine nitrate in the propellant break and decompose to form hydroxylamine,hydrazine,and nitric acid.The endothermic stage is mainly affected by the number of hydrogen bonds in the monopropellant.The second stage is the propellant decomposition stage,which is triggered by the decomposition of nitric acid and hydroxylamine,generating NH2,NO2,and OH.OH is the main oxidizing substance that reacts with hydrazine and methanol to produce a large amount of water.The decomposition of hydrazine mainly depends on dehydrogenation with OH,and generates N2H3.N2 and H2 are the final products.The propellant formulation only has a significant impact on the reaction with OH.Reducing the proportion of methanol can significantly increase the reaction rate of fuel,while promoting the dehydrogenation of hydrazine molecules and increasing the initial decomposition rate of propellant.Increasing the content of hydroxylamine nitrate can promote the decomposition of methanol.However,due to the low rate constant of the reaction of hydrazine,the reaction rate of the propellant decomposition is reduced.
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