Experimental And Modeling Investigation Of Acetylene And C₉H₁₂ Kerosene Surrogate Fuels Oxidation At Low Temperature

As one major share of liquid transportation fuels,jet fuel is utilized to power both civil and military aircrafts.Developing a detailed kinetic model describing the combustion characteristics of jet fuel is of practical significance to reduce pollutant emissions and enhance combustion efficiency.However,jet fuel consists of hundreds of chemical components from multiple classes,including chain alkanes,branched alkanes,cycloalkanes and aromatics.Due to the complex nature of jet fuel,surrogate fuels with representative components including aromatic species have been widely accepted to emulate the parent fuel and reduce the size of practical fuel model.This dissertation has investigated systematically the low-temperature oxidation characteristic of acetylene,iso-propylbenzene,1,3,5-trimethylbenzene and surrogate in the jet-stirred reactor using GC and GCMS technologies.Based on the experimental data and quantum chemical calculation results,one surrogate kinetic model covering gas fuel,single-component C₉H₁₂ aromatic fuels and two-component surrogate fuel was comprehensively validated to guarantee the universality and applicability of current model in the wide experimental conditions.In chapter 1,acetylene serves as one of key precursor of aromatics,which leads to the formation of polycyclic aromatic hydrocarbons（PAH）and soot during the combustion of many hydrocarbon jet fuels,particularly under fuel-rich conditions.C₉H₁₂ alkylbenzene compounds like iso-propylbenzene and 1,3,5-trimethylbenzene are major representative components of many surrogates for transportation fuels,which could simulate the combustion characteristic of alkanes,aromatics and alkylbenzene.Based on the experimental and modeling investigations of single component aromatic fuels,the best road to study the combustion characteristics of real jet fuel is to develop the detailed kinetic mechanism for surrogate fuel,which contributes to the goal of reducing pollutant emissions and enhancing combustion efficiency.In chapter 2,the low-temperature oxidation apparatus of gas and liquid fuels,the history and design principle of key device jet-stirred reactor（JSR）were briefly introduced.The rationality of current jet-stirred reactor was also validated by fluid mechanical calculations.For the kinetic model section,the quantum chemical calculation was described on the determination of reaction route and rate constants of elementary steps.The history of Chemkin software,the detailed information of inputted reaction mechanism,thermodynamic data and transport data and the common analytic tools were also presented in this chapter.Acetylene,one of precursors of aromatics,low-temperature oxidation was investigated in a JSR for four equivalence ratios（Φ=0.5-3.0）over the temperature range of 600-1100 K at atmospheric pressure in chapter 3.17 intermediates were detected and identified by GC.A detailed kinetic model including 295 species and 1830 reactions was developed that provided a reasonable agreement with measurements.The addition of H-atom and the reaction with O constitute the two major channels for C2H2 consumption.Under the conditions of the present experiments,C5H5CH2 isomers play an important role in the formation of benzene.The formation reaction sequence C2H3→iC4H5→fulvene→C5H5CH2→C6H6 is the main source of benzene ring formation at temperatures below 1000 K.the contribution to the formation of benzene ring from the reaction route C5H5+CH3→CSH5CH3→（fulvene or C5H5CH2 radicals）→C6H6 increases with temperature.Furthermore,the current model shows a satisfactory prediction of ignition delay times for C2H2 reported in literature.A study of the low-temperature oxidation of the iso-propylbenzene（IPB）,one of the representative C₉H₁₂ aromatic fuel among surrogate fuels,has been investigated in a JSR over the temperature range of 700-1100 K at atmospheric pressure from fuel-lean to fuel-rich condition in chapter 4.25 stable intermediates including light hydrocarbons,oxygenated and aromatic compounds were identified by online GC and GC-MS after sampling from the outlet gas.A new model involving 306 species and 1985 reactions for the oxidation of IPB was proposed whose predictions were in satisfactory agreement with the mole fraction profiles obtained in JSR.The primary Hatom abstraction of the side isopropyl chain has significant promoting effect;the H-abstraction from the tertiary position of side isopropyl tends to play an inhibiting effect in both cases.The dominant consumption channel of IPB proceeds via the abstraction of benzylic H atom to produce iso-phenylpropyl radicals for both cases.The simulation and experimental results shows that styrene was the most abundant monocyclic aromatic intermediates for IPB in low temperature oxidation.Aim to understand the kinetics process of 1,3,5-trimethylbenzene（T135MB）,another representative C₉H₁₂ aromatic fuel among surrogate fuels,a detailed kinetic model of T135MB was proposed to simulate the combustion of T135MB in chapter 5,which is based on the previous experimental data and quantum chemistry calculation.The proposed mechanism not only predicts well the formation of stable intermediates especially growth of aromatics,in low-temperature oxidation of T135MB,but also simulates well the experimental data of T135MB oxidation in flow reactor as well as global combustion property ignition delay times.The dominant consumption channel for T135MB oxidation is the H-abstraction reactions to form 3,5-dimethylbenzyl radicals,while other reaction pathways like reaction with O/OH radical to generate 1,3,5-trimethylphenoxyl/1,3,5-trimethylphenyl and ipso-addition to form m-xylene play minor roles.The sensitivity analysis reveals that OH and 3,5-dimethylbenzyl radicals play crucial roles in the consumption of T135MB.This work establishes a foundation for the further investigation of surrogate fuel containing T135MB under wide experimental conditions.On the basis of previous T135MB kinetic investigation,the low temperature oxidation of n-decane/T135MB mixture as a surrogate for JP-8 has been investigated in a JSR over the temperature range of 500-1100 K at atmospheric pressure under fuel-rich condition in chapter 6.Mole fraction profiles of 29 intermediates including light hydrocarbons,oxygenated and aromatic compounds were identified by GC techniques.In general,the concentrations of intermediates exhibit bimodal distributions from 550 K in the oxidation of surrogate.By considering the updated rate constants of T135MB and coupling reactions between T135MB and n-decane,a detailed kinetic mechanism involving 910 species and 5329 reactions was established with a reasonable prediction.The low temperature chemistry of surrogate was analyzed through the NTC behavior below 800 K.T135MB in surrogate is mainly consumed through the H-abstractions by OH radicals in the NTC region,while neat T135MB decay is governed by H-abstractions with H-atoms,OH and CH3 radicals at temperatures higher than 925 K.In addition,the model was also validated against the experimental data on n-decane and JP-8 jet fuel combustion,including species profiles in low temperature jet-stirred reactor oxidation and high temperature flow reactor pyrolysis as well as ignition delay times.It is concluded that the low-temperature oxidation experiments of aromatics precursor acetylene,typical C₉H₁₂ alkylbenzene fuel such as IPB and T135MB and kerosene surrogate fuel in this work enrich the experimental database of basal combustion,particularly in getting the direct evidence of formation of aromatic from acetylene under low-temperature condition.In addition,the developed kinetic model not only simulates well the concentration of pyrolysis and oxidation of acetylene,IPB,T135MB and surrogate,but also predicts well the global combustion parameters such as ignition delaytimes.These extended results presents the better accuracy,universality and applicability of current model,and will benefit for further application of practical jet fuels,particularly for reducing pollutant emissions,enhancing combustion efficiency and low-temperature auto-ignition.