Study On The Ignition Characteristics And Combustion Chemical Kinetics Mechanism Of 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene And N-propylbenzen

The combustion chemistry of engine combustion chambers and fuels is a common key scientific problem for aero engines,where the combustion chemistry is the basis for combustion chamber design.Aviation paraffin is a common fuel for aero engines,and it is difficult to accurately determine all of its components due to the complexity of the actual components of aviation paraffin.The concept of fuel substitution models is commonly used in practical engineering applications and scientific research,whereby a mixture of three to five single component hydrocarbon fuels of a defined molecular formula in a certain proportion is used instead of the true composition of the actual aviation kerosene.There are many different types of aviation paraffin,but the alternative model components generally include the four main categories of straight-chain alkanes,branched alkanes,cyclic alkanes and aromatic hydrocarbons.The three C₉H₁₂ fuels 1,2,4-trimethylbenzene（124TMB）,1,3,5-trimethylbenzene（135TMB）and n-propylbenzene（NPBENZ）are common representatives of the aromatic hydrocarbon substances used in aviation paraffin alternative fuel model compositions and one of them is often used as an aromatic component in different aviation paraffins.Due to the differences in the molecular structure of the three C₉H₁₂ fuels,their ignition and combustion characteristics and their combustion chemical kinetic mechanisms must also be quite different,and an in-depth study of the ignition and combustion characteristics of the three C₉H₁₂ fuels is urgently needed to investigate the differences between them.The results of this study will not only provide a theoretical basis for the selection of the optimum fuel component for the aviation paraffin replacement model,but will also provide basic data for the design of the combustion chamber of an aircraft engine using the relevant fuel components.Based on this,a detailed study of the ignition characteristics of each of the three C₉H₁₂ fuels was carried out using a high pressure surge tube experimental system.Based on this,a combustion chemical kinetic mechanism covering the three fuels mentioned above was developed,and a systematic numerical simulation of the ignition process of the three fuels was carried out using this mechanism.The main research elements and conclusions of the thesis are as follows:（1）The ignition delay times of 124TMB,135TMB and NPBENZ at different pressures（2.0 bar,5.0 bar and 10.0 bar）and equivalent ratios（0.5,1.0 and 2.0）in the medium to high temperature（1090-1600 K）range were measured using a radical tube experimental system,and the detailed investigation of the effects of pressure,temperature and equivalent ratio on the ignition characteristics of the three fuels respectively was carried out.On this basis,the experimental results were fitted in Arrhenius form to obtain the dependence of the ignition delay time on the initial ignition pressure,temperature,equivalence ratio and fuel and oxygen concentrations for each of the three fuels.The experimental results show that the reactivity of the three C₉H₁₂ fuels increases with increasing ignition pressure for a given equivalence ratio,as evidenced by the decrease in ignition delay time with increasing pressure;at constant pressure,the increase in equivalence ratio leads to an increase in ignition delay time for124TMB,while the variation of ignition delay time with equivalence ratio for 135TMB and NPBENZ shows the opposite pattern to that of In addition,comparing the ignition delay times of the three fuels under the same ignition conditions showed that the overall reactivity of the three C₉H₁₂ fuels was NPBENZ>124TMB>135TMB,and the reactivity of 124TMB and135TMB was similar when the equivalence ratio was increased to 2.0.（2）A general mechanism was developed using the NUIG Mech 1.1 Skeleton mechanism as the base mechanism,which included 1105 species and 6219 radical reactions.Detailed chemical kinetic numerical simulations of the ignition processes of three C₉H₁₂ fuels under different initial conditions were carried out using Chemkin Pro software,and the simulation results showed that the mechanism could accurately predict the ignition characteristics of the three fuels.（3）Detailed chemical reaction kinetic analyses were carried out for the ignition and combustion processes of the three fuels.Among the results,sensitivity analysis shows that most of the reactions of 124TMB and 135TMB in the early stage of ignition are related to dehydrogenation reactions and fuel radical depletion reactions,while the reactions that play a key role in NPBENZ are initial dehydrogenation reactions,decomposition reactions and reactions involving important C₀-C₄ small molecules.Analysis of the reaction pathways shows that the initial reaction pathways in NPBENZ are dominated by dehydrogenation and decomposition reactions,followed by fuel radical depletion mainly throughβ-cracking reactions,while the initial reaction pathways in 124TMB and 135TMB are completely dominated by dehydrogenation reactions,with subsequent fuel radical recombination reactions playing an important role in ignition.