吸热型碳氢燃料正辛烷的热分解机理

Mechanism of Thermal Decomposition of Endothermic Hydrocarbon Fuel n-Octane

利用反应分子动力学方法,对正辛烷在不同温度条件下的热解特性进行研究,并用密度泛函理论(DFT)对结果进行验证比较。结果表明:正辛烷初始反应为八种热解均裂反应,分别为四种碳碳键断裂和四种碳氢键断裂,且碳碳键比碳氢键更容易发生断裂,分子端部的化学键断裂比较困难。讨论了温度对热解产物的影响,热解的主要产物是H_2、CH_4、CH_2=CH_2,其他产物为CH_3-CH_3。H_2有两种形成机理,分别是自由基攻击反应和自由基间结合反应。CH_4有两种形成机理,与H_2的相似。CH_2=CH_2的形成机理为大分子自由基β键断裂反应。本工作从分子尺度研究了正辛烷的热解机理,为其他吸热型碳氢燃料的热裂解特性研究提供了参考。

The pyrolytic feature of n-octane was investigated by utilizing ReaxFF molecular dynamics(RMD)simulations under the condition of different temperatures and the result was compared with density functional theory(DFT)simulations.The result indicates that there are eight main pathways in the initial reaction path of n-octane,which are divided into C-C bond rupture and C-H bond rupture.C-C bond rupture is easier than C-H bond rupture and it is difficult to break the bonds at the end of the molecular.The effect of temperature on the pyrolytic product was discussed and the main products of the pyrolysis are H2,CH4,CH2=CH2,and CH3-CH3 molecule is also observed in the pyrolysis process.The formation of H2 has two mechanisms,the reaction of the free radical attacking and the reaction of the combination of the free radicals.The formation mechanism of CH4 is same as that of H2.The formation mechanism of CH2=CH2 isβbond break reaction of macromolecular radical.Our work presents the mechanism of n-octane thermal decomposition from a molecule level and provides a reference for studying the thermal decomposition of endothermic hydrocarbon fuel.