Reactive Molecular Dynamics Simulation On Thermal Decomposition Mechanism Of Endothermic Hydrocarbon Fuels Initiated By Nitroethane

Normal alkanes,cycloalkanes and branched hydrocarbons are important components of endothermic hydrocarbon fuels.The present work conducts the reactive molecular dynamics?RMD?simulations based on reactive force field to compare the thermal cracking of iso-octane,n-heptane and methylcyclohexane?MCH?with the same carbon atom number initiated by nitroethane,focusing on initial decomposition temperature,intermediates and product distribution,and the related kinetics.From the RMD simulations,we find nitroethane can accelerate endothermic hydrocarbon fuels decompositions,since the C–NO₂ bond rupture of nitroethane can proceed at relatively lower temperatures to produce the reactive radicals compared to the C–C bond cleavage of n-heptane,MCH and iso-octane to start the free radical chain reactions,but the promoting effect becomes weaker after it reaches a certain level with temperature.Reasonable Arrhenius parameters estimated from RMD simulations based on first-order kinetic analysis compare well with experimental results.The observed difference of pyrolysis behaviors and kinetic parameters between n-heptane and MCH can be ascribed to their molecular structure,coinciding with experimental observations.In the presence of nitroethane,reductions of initial temperature and activation energy for n-heptane decomposition are larger than those for MCH decomposition.More alkenes are observed in n-heptane decomposition compared to MCH decomposition.In addition,through the reaction molecular dynamics simulation of the high temperature cracking of iso-octane,the reaction pathway diagrams of iso-octane pyrolysis in the initial stages was constructed.Due to the endothermic capacities of fuel being sensitive to the yields of unsaturated hydrocarbons,in this work,the reaction paths of ethylene,acetylene and propylene in iso-octane pyrolysis products were analyzed in detail.These results indicate that RMD simulations can provide important insights at the atomistic level on the thermal cracking of endothermic hydrocarbon fuels initiated by nitroethane under supercritical conditions.