Initial Pyrolysis And Oxidation Pathways Of RP-3 Fuels And Surrogates Revealed By Reaxff MD Simulations

Aeroengines are the core equipment in the fields of national defense and transportation,reflecting the technological and industrial capabilities of a country.The study towards the chemical reaction mechanism of the combustion process is of vital importance to get insight view of combustion.Exploring the combustion mechanism of aviation fuel is one of the key problems to be solved for the numerical simulation of engine combustion and the further promotion of engine design.China No.3 aviation fuel?RP-3?is broadly used in aviation industry.Due to the complex composition of RP-3,the method of constructing a surrogate fuel model is usually used to simplify the complexity of the model.At present,a variety of surrogate models for RP-3have been proposed,but there are some differences in the types and proportions of hydrocarbons in these models,which brings certain difficulties for the selection and application of the model.In this paper,the reaction mechanism of high temperature pyrolysis and oxidation of RP-3 was systematically studied by molecular dynamics simulation method based on reactive force field?ReaxFF?.To evaluate the reactivity of surrogate models and get better understanding of the high-temperature pyrolysis and oxidation mechanism of aviation fuel RP-3,a multi-component?45-component?model was constructed as a baseline model of which the composition is closer to real fuel.Reactive molecular dynamics simulations were performed for the 45-component model and two surrogate models of 3-component and 4-component.Compared with the weight fraction of C₂H₄ in 45-component model,the 4-component surrogate is 15%higher,the 3-component surrogate is 10%higher.The C₂H₄ yield overestimate of the two surrogates is attributed to the much higher normal paraffin of 4-component surrogate?86.5%?and 3-component surrogate?73.0%?over the 45-component model?26.7%?.The overestimate of C₃H₆ production in 3-component model is greatly influenced by the radicals containing methyl side chains generated from ring-opening reactions of cycloparaffins.Therefore,the structure of the fuel molecules and the proportion of each component directly affect the production of ethylene and propylene,which are important pyrolysis products,indicating that the reactivity comparison method based on the reactive molecular dynamics simulation has the potential to provide further optimization for the surrogate fuel model.Based on the results of pyrolysis simulation,high-temperature oxidation simulation was conducted for further exploration of the oxidation characteristics.Focusing on the evolution of the main products in the oxidation process,the oxidation and pyrolysis simulation results under the same simulation conditions were compared.There is still a significant difference in the yield of ethylene between surrogate and the detailed components model during oxidation process.This also leads to a significant difference in reaction network and the combustion products between different models.In conclusion,this paper studies the chemical reaction of the detailed component model and the typical surrogate fuel model under high temperature pyrolysis and oxidation process for RP-3.This work intends to provide insight view of the high-temperature combustion mechanism of aviation fuel and furthermore,the work is also expected to shed light on constructing a more reasonable surrogate model which could provide a more detailed and reasonable reaction mechanism.