| The clean and efficient utilization of fossil fuels is an important issue in the modern society.With the rapid development of the world aviation industry,the consumption of aviation fuel has increased rapidly in the 21st century.When the fuel is burned insufficiency,it will affect the efficiency of the engine and produce a large amount of soot which could pollute the environment.Therefore,it is of great significance to improve the combustion efficiency of aviation fuel and reduce the pollutant emissions in the combustion process for the realization of energy conservation and emission reduction of fossil fuel.Aviation fuel originated in the mid-20th century.After decades of development,many types of aviation fuel have been used in military and civil aircraft.The research on chemical reaction kinetic of aviation fuel is helpful to understand the combustion process of aviation fuel,analyze the formation mechanism of pollutants in the combustion process and optimize the combustion chamber design of engine.Due to the complexity of the components in aviation fuel,it is difficult to directly establish a detailed mechanism.In order to study the combustion chemistry mechanism of aviation fuels,surrogate fuels have been widely used for mechanism establishment in the past decades.Moreover,acetylene,as an important precursor of soot,has attracted more and more attention.Based on the aviation surrogate fuel reaction kinetic and the mechanism of soot formation,the consumption and formation process of aromatic components were mainly studied through experiments and kinetic mechanism research in this paper.Firstly,the hazards brought by the utilization of fossil fuels,the development process and main types of aviation fuels,the development trend of aviation fuel of China in recent years and the importance of developing reaction kinetic mechanism research related to aviation surrogate fuel has been introduced.Besides,this paper briefly summarized the research status and shortcomings related to soot generation,acetylene,iso-propylbenzene and aviation surrogate fuels in recent years,and introduced the experimental devices used in the study of reaction kinetic,such as flow tube reactor,laminar premixed flame experimental device,rapid compressor machine and so on.Finally,according to the above discussion,the research contents and purposes of this paper was presented.Secondly,the experimental devices and simulation methods involved in this paper were introduced in detail.The experimental devices used in this paper are the flow tube pyrolysis reactor and the high pressure jet stirred reactor.In Chapter 2,the structure and usage of these two devices were introduced in detail,and the temperature distribution in these two devices was measured.The reliability of the device was verified by repeating acetylene oxidation experiment at lean condition.The development process of CHEMKIN software and its three core modules,namely chemical kinetic mechanism,thermodynamic data,and transport data profiles were introduced.In addition,the definition and significance of sensitivity and reaction pathways analysis were also briefly described.Then,in order to study the oxidation characteristics of acetylene under high pressure,oxidation experiment of acetylene has been investigated in a newly designed high pressure jet stirred reactor with equivalence ratios Φ=0.5-3.0 in the temperature range of 650-900 K at 12 atm.18 products and intermediates were detected in the experiment process.The initial consumption temperature of acetylene was not obviously affected by Φ.However,with Φ increasing,the productions of intermediates increase significantly.Moreover,benzene,toluene and styrene were only detected at Φ=3.0.Meanwhile,detailed kinetic mechanism which consists of 299 species and 2041 reactions has been developed with reasonable predictions against the present data.Based on the developed mechanism,the reaction pathways and sensitivity analysis in the acetylene high pressure oxidation process were carried out.The analysis showed that H and OH radicals played an important role in the consumption of acetylene.Besides,the formation pathways of aromatics was analyzed.The results of high pressure oxidation experiment were compared with those of atmospheric pressure oxidation experiment.The results show that the increase of pressure can promote the fuel consumption and aromatics generation.The mechanism was used to simulate the atmospheric pressure experiment,and the differences of acetylene consumption pathways and aromatics generation pathways under different pressures were compared.Next,in order to study the pyrolysis characteristics of iso-propylbenzene at variable pressure,pyrolysis study of iso-propylbenzene at 0.04 and 1.00 atm was carried out by using synchrotron photoionization and molecular beam mass spectrometry techniques.Iso-propylbenzene was diluted to 0.5%concentration by helium and heated to 798-1148 K in the flow tube reactor.A large number of intermediates were detected during pyrolysis,including light hydrocarbons,mono aromatics and poly aromatics.A detail mechanism involving 306 species and 1990 reactions was developed by updating IPSO-addition and unimolecular dissociation reactions of iso-propylbenzene as well as reactions related indene and naphthalene.The mechanism could reproduce the pyrolysis progress of iso-propylbenzene and intermediate mole fraction profiles reasonably.The reaction pathways and sensitivity of iso-propylbenzene pyrolysis process were analyzed through the developed mechanism.In addition,the oxidation characteristics of iso-propylbenzene under high pressure were studied in the high pressure jet stirred reactor.The oxidation pressure of iso-propylbenzene was 12 atm,the Φ were 0.4 and 2.0,and the experimental temperature range was 625-950 K.More than 30 kinds of products and intermediates were observed,including inorganic compounds,small molecular hydrocarbons,oxygenates,mono aromatics and poly aromatics.A large amount of methane,α-methylstyrene,phenol and formaldehyde were produced during the experiment.Indene,naphthalene,biphenyl and stilbene were also detected.Combined with the existing research results,the oxidation process of iso-propylbenzene was analyzed,and the necessity of high pressure oxidation kinetic research of iso-propylbenzene was pointed out.Finally,a detailed chemical reaction kinetic mechanism involving 1181 species and 6964 reactions was developed for the surrogate fuels of JP-8 and RP-3.The low temperature oxidation characteristics of the two surrogate fuels were compared regarding the aspects of components difference,negative temperature coefficient(NTC),intermediates and products formation.The reaction pathways and sensitivity of these two surrogates were analyzed through the developed mechanism.According to reaction pathways analysis,1,3,5-trimethylbenzene is consumed mainly by methyl ion reactions.However,consumption of n-propylbenzene is dominated by decompositions on the propyl group.Sensitivity analysis indicates that the reactions H2O2(+M)<=>OH+OH(+M)and HO2+HO2<=>H2O2+O2 are the most promoting and inhibiting reactions on 1,3,5-trimethylbenzene and n-propylbenzene consumption,respectively.Moreover,the present mechanism could reproduce the ignition delay times of JP-8 aviation and RP-3 surrogate fuels.As the developed mechanism could simulate the macro and micro characteristics of fuel and surrogate fuel reasonably,it will be helpful to deepen the understanding of combustion process of aviation fuels.In conclusion,the reaction kinetics of acetylene and iso-propylbenzene were studied in a high pressure jet stirred reactor and a flow tube pyrolysis device.The kinetic mechanisms relating to acetylene high pressure oxidation and iso-propylbenzene pyrolysis were developed,and the initial formation process of soot was studied.In addition,based on the low temperature oxidation experimental data of JP-8 and RP-3 surrogate fuels,a comprehensive reaction kinetic mechanism of these two surrogate fuels was established,and the differences of oxidation characteristics of these two surrogate fuels were compared and analyzed.The experimental and simulation results in this paper will help to further understand the soot formation process in the combustion process of aviation fuel,and provide experimental and theoretical support for the clean and efficient utilization of aviation fuel. |
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