| The combustion of fossil fuel provides a large amount of world energy demand, esperically for the transportation energy which is closely related to people’s daily life. The combustion of fossil fuel is also the major contributor for the air pollution. Therefore, two main focus for application combustion studies are the enhancement of combustion efficiency and the reduction of pollutant emission. Many efforts have been made to develop new combustion technology and new combustion devices. Computational fluid dynamics (CFD) simulation provides low-cost and convinent ways to investigate the combustion processes in combustion facilities and was commonly used to assist the engines desining as well as develop new types of engines. The simulation of combustion processes in engine is complexed, which coupled chemical reactions and flow properties and chemical reactions play significant roles.Many components were found in real transportation fuels, such as normal alkanes, branched alkanes, cycloalkanes and aroamtics. Thus it is impossible to study the combustion kinetics of transportation fuels by suing real fuels. Surrogate fuels were commonly used for the combustion kinetic studies. Surrogate fuels constitute some typical kinds of fules emerged in the real fuels, and their ratio is adjusted to match the chemical properties and thermophyscial properties of real fuels. To develop the kinetic model of a surrogate fuel, the first step is to develop the kinetic model of the single components constituted. The kinetic mdoel developed from a single laboratory combustion research under specific pressure or temperature conditions is usually less persuasive. A comprehensive kinetic model which is developed by validating different sets of experimental data under different conditions is more plausible. Aromatic hydrocarbons are major components of petroleum-based transportation fuels and are widely used as major components of surrogate fuels for gasoline, diesel oil and kerosene. They are also key precursors of soot which is an important combustion-derived air pollutant known to be harmful to both the environment and human health. Consequently, understanding the combustion chemistry of aromatic hydrocarbons is crucial for the development of kinetic models of surrogate fuels, and increases our knowledge on the gas phase molecular growth process in soot formation mechanism.In this work, the flow reactor pyrolysis and laminar premixed flames of toluene, ethylbenzene, styrene,n-propylbenzene and n-butylbenzene were studied using synchrotron radiation vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). The flow reactor pyrolysis experiments were performed from low to atmospheric pressure and at high temperatures. The low pressure laminar premixed flames were studied at different euquivalence ratios from fuel-lean condition to fuel-rich condition. Many species were detected, including the radicals, isomers and polycyclic aromatic hydrocarbons. Moreover, the jet-stirred reactor (JSR) oxidation of alkylbenzenes at 10 atm and different equivalence ratios were investigated using Fourier transform infrared (FTIR) spectroscopy and gas chromatrography (GC) and GC-MS technique. The GC was combined with flame ionization detector (FID), thermal conductivity detector (TCD) and MS and different columns.Base on the present experimental results and recent theoretical progresses, the combustion model of alkylbenzene was developed and validated against a variety of experimental data. Some major distinguished poins about the model developed include:1) a comprehensive validation work was peformed for C0-C4 small molecules and 1,3-cyclopentadiene, which aimes to ensure the accuracy of the proposed submechamism; 2) in the kinetic model of toluene, new elemental reaction pathways about benzyl radical decomposition were proposed to replace the former global reaction pathways. Besides, the formation mechanism of polycyclic aromatic hydrocarbon species from the decomposition prodcts of benzyl radical was also proposed. The role of methylphenyl radical in the oxidation of toluene was also emphasized. Moreover, the model was widely validated by simulating as many as literature reported experimental data, which aimes to enhace the accuracy of the model when used fot gasoline surrogate model development; 3) in the model of ethylbenzene and styrene, our work proposed the first comprehensive ethylbenzene and styrene mechanism. The role of benzylic C-C bond and double bond in styrene molecule are emphasized. The new pathways for O addition reactions of styrene were proposed based on experimental results; 4) in the model of n-propylbenzen and n-butylbenzene, some newly proposed low temperature oxidation pathways were added in the present model. Moreover, the model was widely validated to ensure its accuracy when using for the combustion simulation of surrogate fuels of diesel fuel sand kerosene fuels.The common used reacting flow simulation codes such as CHEMKIN, OpenSMOKE and LaminarSMOKE were used for the simulation. Mehamism analysis methods such as rate flow analysis, sensitivity analysis, element flow analysis, quassi steady state (QSSA) analysis and uncertainty analysis were used. Modeling analyses were performed to provide insight into the chemistry of fuel decomposition and aromatic growth. In the flow reactor pyrolysis, toluene is mainly consumed by H-atom abstraction and unimolecular decomposition C-H reactions, producing benzyl radical. The subsequent decomposition of benzyl produces C5-C7 products. These products either decompose to smaller products or participate in the formation of PAHs. The important reactions for the formation and consumption of some large mono cycliaromatic hydrocarbons and typical polycyclic aromatic hydrocarbons were also discussed. It is concluded that benzyl, fulvenallenyl and cyclopentadienyl radicals, especially the two C7 radicals, play important roles in the formation of polycyclic aromatic hydrocarbons. In the jet stirred reactor oxidation, toluene is mainly consumed by H-atom abstraction reactions to produce benzyl. In the combustion of styrene, the double bond in the molecule of styrene easily react with O atom to form different products, thus styrene presents higher oxidation reactivity than pyrolysis reactivity. The benzylic C-C bond in the ethylbenzene molecule is the weakest bond, which can be dissociated with low activation energy, thus ethylbenzene presents relative high pyrolysis and oxidation reactivity. For longer alkylbenzenes, n-butylbenzene shows the low temperature reactivity and negative tmepperature coefficient (NTC) zone while n-propylbenzene has no NTC zone, although compared with ethylbenzene and toluene, n-propylbenzene presents higher low-temperature reactivity. In the combustion of n-propylbenzene and b-butylbenzene, phenylalkenes are among the abundantly produced primary products, the step-wise H-loss reactions and ring closure reactions convbert the phenylalkenes to bicyclic aromatic hydrocarbons. These pathways are also the main formation fuel structure specific PAHs formation pathways in the combustion of n-propylbenzene and n-butylbenzene.Moreover, the soot formation kinetics was combined with the model to investigate the formation kinetics of soot from the combustion of alkylbenzene. The PAH-soot model was validated by simulating the ISF standard sooting flames. The PAH-soot formation model was then used to simulate the sooting properties in the combustion of alkylbenzenes. As a conclusion discussion, the present work was further investigate the effect of fuel structure on the combustion properties of alkylbenzene. These properties include both microscopic concentration distributions, soot formation properties and global combustion properties such as ignition delay times, laminar flame propargation speed, extinctions strain rates, etc. as the length of alkyl-chain increases, the reactivity of alkylbenzenes increases, and result in shorter ignition delay times and faster laminar propagation speeds. |
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