Reaction Path and Mechanisms of Li/SF₆ Combustion

Revealing the combustion reaction mechanism of Li/SF₆ fuel is the key basis for constructing the combustion kinetics model and efficiently organizing the combustion process. However, it is difficult to reveal the stepwise reaction mechanism of Li/SF₆ combustion by existing experimental tests and macroscopic simulation methods. This paper studied the microscopic reaction processes of Li and SF₆ by combining the ReaxFF molecular reaction simulation and first-principles calculation method. The dynamic evolution characteristics of reactants and product components were analyzed, and the main reaction paths and reaction heat were obtained. It is found that the breakage of the S-F bond in SF₆ molecules is the initial stage of the reaction, and LiF is the main product of the initial reaction. As the reaction progresses, the excessive Li forms Li₂ and bonds with S to form Li₂S. At the later stage of the reaction, two LiF molecules combine with each other to produce Li₂F₂. Based on the variation of reactant concentration, the total reaction rates of Li and SF₆ are obtained. The results show that the total reaction rate is positively correlated with the reactant concentration and reactant proportion because the rise of reactant concentration or proportion leads to a larger collision probability between reactant molecules. The impact of initial temperature on the total reaction rate is relatively small. According to the enthalpy value of the reactants obtained from the first-principles, the heat release of each stepwise reaction is calculated. The reaction heat for Li/SF₆ combustion is −2 216.7 kJ/mol, which is close to the theoretical and experimental values. The research results provide an effective way to reveal the stepwise reaction mechanism and calculate the reaction heat of complex combustion reactions.