Li/SF_(6)燃烧反应路径及机理研究

Reaction Path and Mechanisms of Li/SF_(6)Combustion

揭示Li/SF_(6)燃烧反应机理是构建燃烧动力学模型、高效组织燃烧过程的关键基础,但是现有实验测试以及宏观模拟方法难以揭示Li/SF_(6)燃烧的分步反应机理。文中结合ReaxFF反应分子模拟和第一性原理计算方法研究了Li和SF_(6)的微观反应过程,分析了反应物和产物组分的动态演化特性,获得了主要反应路径及其反应热。研究发现,反应的起始过程为SF_(6)分子S-F键的断裂,LiF是反应初始时刻的主要产物;随着反应的进行,多余的Li形成Li_(2)并与S成键形成Li_(2)S;反应后期,2个LiF分子结合反应形成Li_(2)F_(2)。基于反应物浓度变化获得了Li和SF_(6)的总反应速率,结果表明,总反应速率与反应物浓度、反应物比例呈正相关关系,这是因为反应物浓度或比例的增大均会导致反应物分子之间碰撞概率的增加;初始温度对总反应速率的影响则相对较小。结合第一性原理得到的反应物焓值,计算各个分步反应的放热量,进而得到Li/SF_(6)的反应热为-2216.7 kJ/mol,与理论值及实验值均接近。研究结果为复杂燃烧反应的分步反应机理揭示和反应热计算提供了有效途径。

Revealing the combustion reaction mechanism of Li/SF_(6)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/SF_(6)combustion by existing experimental tests and macroscopic simulation methods.This paper studied the microscopic reaction processes of Li and SF_(6)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 SF_(6)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 Li_(2)and bonds with S to form Li_(2)S.At the later stage of the reaction,two LiF molecules combine with each other to produce Li_(2)F_(2).Based on the variation of reactant concentration,the total reaction rates of Li and SF_(6)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/SF_(6)combustion is−2216.7 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.