| The combustion of fossil fuels provides most of the energy used worldwide.However, combustion processes also produce environmental pollutants. Therefore,effectively improving the combustion efficiency of fossil fuels and minimizing the environmental problems are the goals that people have been pursuing. A comprehensive understanding of the chemical kinetics in the combustion process is very crucial in order to improve combustion efficiency and reduce emissions from combustion.Transportation fuels are typical fossil fuels, such as gasoline, kerosene and diesel. They have very complex components, which are made up of hundreds of hydrocarbons, e.g.n-alkanes, cycloalkanes, branched alkanes and aromatics.N-alkane is an important constituent in real transport fuels and the carbon chain length of n-alkanes in gasoline, kerosene and diesel are quite different. For example,the average carbon chain length of n-alkanes in diesel is much longer than that in gasoline. Therefore, present work studied three different carbon chain length n-alkanes,i.e. n-decane, n-dodecane and n-tetradecane. First, present work studied the combustion process of these three fuels based on present experiments and kinetic models in order to study the fuel decomposition pathways, the formation and decomposition pathways of representative intermediates and products. Second, the comparative studies of three n-alkanes with different carbon chain lengths is applied to study the effects of carbon chain length of on combustion process of n-alkanes. Cycloalkanes have the completely different structures from n-alkanes. Present work studied the combustion chemistry of decalin experimentally and numerically. Decalin has two six-membered rings, and has the same carbon number with n-decane. Because of the existence of two six-membered rings, decalin has two unsaturation numbers. Thus, the hydrogen atom numbers of these two fuels are different. The different structures of decalin and n-decane indicate the different thermodynamic and kinetic characters during the combustion process. The branched alkane is another main constituent of real transportation fuels. Compared with n-alkanes, branched alkanes have more carbon types than n-alkanes. That is, n-alkanes have only primary and secondary carbons, while the branched alkanes may contain primary, secondary, tertiary and quaternary carbons. In this work, iso-octane, namely 2,2,4-trimethylpentane, has been selected as the target branched alkane to study. Iso-octane has four carbon types, and is often used as the representative branched alkane in the surrogate fuels of gasoline and kerosene. In addition, more and more studies were focused on the combustion chemistry of mixed fuels. Researchers thought that mixing two or more different fuels to develop the mixed fuels can regulate the combustion chemistry of the mixed fuels, such as improving combustion efficiency and reducing pollutants. Based on this concept, present work studied the combustion chemistry of iso-octane and its mixture with dimethyl ether and diethyl ether mixture fuel experimentally and numerically.In this work, the flow reactor pyrolysis experiments of n-decane, n-dodecane, n-tetradecane and decalin were performed under atmospheric and lower pressures. The laminar premixed flames of n-decane and decalin were studied under low pressures.Both using synchrotron vacuum ultraviolet photoionization mass spectrometry as diagnostic method. In the flow reactor pyrolysis experiments, the pyrolysis intermediates and products were identified by using the photoionization efficiency spectra, including the active radicals and isomers. Mole fractions of pyrolysis species were obtained by changing the temperature of pyrolysis furnace. In the laminar premixed flame experiments, in addition to the identification of species with photoionization efficiency spectra, the signal of species at different position above the axial direction of burner surface were recorded, which was evaluated to the mole fractions of species as a function of distance from the burner surface. Besides, the laminar premixed flames of iso-octane, and iso-octane/ether mixture fuels were studied in this work using electron ionization molecular-beam mass spectrometer. Mole fractions of species in these premixed flame was obtained as functions of distance above the burner surface. Experimental results of species, including active radicals, provide evidences and basis for the construction and validation of kinetic models.Based on present experimental results, detailed kinetic models of n-decane, n-dodecane and n-tetradecane were developed in this work. Simulations was carried out with Chemkin-Pro software. Rate of production analysis and sensitivity analysis were performed in order to reveal the comprehensive chemical reaction pathways in the combustion of n-alkanes. Compared to the reference n-alkane kinetic models, the main innovation of present n-alkane models is that the pressure-dependent rate constants for crucial reactions were used, such as unimolecular dissociation reactions of n-alkanes,unimolecular dissociation reactions of alkenes, isomerization reactions, unimolecular dissociation reactions of alkyls and so on. Thus, compared with simulation results using the previous n-alkane models, present n-alkane models are more predictive for present flow reactor pyrolysis experiments of n-alkanes under atmospheric and lower pressures,such as the fuel comsumption and and intermediates formation. Moreover, present n-alkane models also include low temperature reactions, thus the models can be also used to predict the low temperature oxidation experiments of n-alkanes. In order to extend the predictability of present n-alkane models to a wider temperature, pressure, and equivalent ratio conditions, present n-alkane models were also validated against literature reported n-alkane experimental data. These include the high pressure shock tube oxidation data, the jet stirred reactor oxidation data, the counter-flow flame data,ignition delay times, laminar flame speeds and so on. Rate of production analysis shows that n-decane, n-dodecane and n-tetradecane are mainly consumed by unimolecular dissociation reactions and H-abstraction reactions in the flow reactor pyrolysis experiments. Sensitivity analysis shows that unimolecular dissociation reactions of n-alkanes have very high sensitivities in the flow reactor pyrolysis experiments. In the laminar premixed flames of n-alkanes, the contribution of unimolecular dissociation reactions of n-alkanes to the fuel consumption is very small, instead, n-alkane is mainly consumed by the H-abstraction reactions.This paper developed the first detailed kinetic model of decalin to solve the problem of the lack of a detailed kinetic model of decalin in the world. Present decalin model can well predict the decomposition of decalin and formations of intermediates and products in the flow reactor pyrolysis experiments and these in the laminar premixed flames experiments. Rate of production analysis and sensitivity analysis were performed to reveal the consumption pathways of decalin, formation and consumption pathways of products. In the flow reactor pyrolysis of decalin, decalin is mainly consumed by the unimolecualr C-C dissociation reactions to produce diradical intermediates. These diradicals will further produce stable monocyclic C10H18 alkene isomers via the hydrogen transfer reactions. Decalin can be also consumed via the H-ion reactions to produce three decalyl radicals. The subsequent consumption of these three decalyl radicals will produce a series of monocyclic aromatic hydrocarbons,such as benzene, toluene, and styrene, which reveals that there are formation pathways of aromatics from the consumption of decalin. In the laminar premixed flames experiments of decalin, decalin is mainly consumed via the H-abstraction reactions.Moreover, besides the hydrocarbon aromatics, several oxygenated aromatics were also detected in the laminar premixed flames. The present decalin model was further validated against literature reported experimental data of decalin, such as shock tube pyrolysis data, jet stirred reactor oxidation data and ignition delay time.Present new laminar iso-octane premixed flame experiment was used to test several representative iso-octane models. Among these literature reported iso-octane models, the one from Pitsch group has a better performance against present iso-octane flame experiments than other models. Besides, reference experiments of iso-octane were also used to test the Pitsch model. Based on these validations, a kinetic model for iso-octane, dimethyl ether and diethyl ether was developed by adding the fuel submechanism of dimethyl ether and diethyl ether to the iso-octane model, which is called as present fuel mixtures model. Present fuel mixtures model can well predict present seven laminar premixed flames, namely iso-octane flame, two iso-octane/dimethyl ether mixtures flames, two iso-octane/diethyl ether mixtures flames,dimethyl ether flame and diethyl ether flame. Present fuel mixtures model was also validated against literature reported iso-octane experimental data, dimethyl ether experimental data and diethyl ether experimental data. At last, the effects of dimethyl ether or diethyl ether addition to iso-octane flames was studied. It was found that ether addition to the iso-octane flame has little impact on the consumption pathways of the iso-octane. However, the ether addition will affect the formations of aldehydes, alkenes and aromatics in the iso-octane flame. |
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