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The oxidation of styrene, one of the main stable intermediates from the oxidation of large alkylated aromatic hydrocarbons, has been investigated in the present work both experimentally and numerically. Experiments were performed using two complementary techniques, spherical bomb for laminar flame speed studies and shock tube for ignition delay time measurements. In particular, the laminar flame speeds of styrene/air mixtures were measured at three different initial temperatures (342 K, 373 K, and 405 K), over a wide range of equivalence ratios (0.75–1.45), for an initial pressure of 100 kPa. In addition, the autoignition of styrene/O 2 mixtures in argon bath gas ( ϕ = 0.5, 1.0, and 1.5) was investigated over a wide range of temperatures (1390–1990 K), at highly diluted conditions (94.3%–99% argon), and for pressures between 110 and 200 kPa. A detailed chemical kinetic model, based on the toluene chemistry by Metcalfe et al . (2011), was developed and validated against the newly obtained experimental results and the flow reactor data available in the literature (Litzinger et al . , 1986). Sensitivity and rate of production analyses were performed and showed that, at the conditions studied herein for the flame speed investigation, the main fuel consumption pathways include the reaction of the fuel with H atoms to form phenyl radical and ethylene or benzene and vinyl radical, with O to form benzyl radical + HCO, and the H-abstraction reactions on both the vinyl moiety and the ring. On the other hand, the analyses performed at the high-temperature, highly-diluted conditions encountered in the shock tube study highlighted the importance of the fuel thermal decomposition steps for the simulation of the ignition delay time measurements. The model was also tested against the low-pressure flame and jet stirred reactor data by Yuan et al. (2015). The results highlight the need for future modifications in the benzene chemistry by Metcalfe et al . and inclusion of pressure dependent rate parameters in order to improve the prediction capabilities of the model. [ABSTRACT FROM AUTHOR]

A combined experimental and kinetic modeling study is carried out to explore the influences of acetylene and ethylene addition on the species formation from toluene pyrolysis. Experiments are conducted separately with four different argon-diluted binary toluene/C 2 mixtures in a single pulse shock tube at a nominal pressure of 20 bar over a temperature range of 1150−1650 K. All the experimental mixtures contain about 100 ppm toluene and different amounts of C 2 fuels (50, 216, 459 ppm acetylene and 516 ppm ethylene). Species concentrations as a function of the temperature are probed from the post-shock gas mixtures and analyzed through the gas chromatography/gas chromatography-mass spectrometry techniques. A kinetic model is developed, which successfully predicts the absolute species concentration measurements as well as the changes brought by the varied fuel compositions. With the neat fuel decomposition profiles as a reference, both fuel components exhibit increased reactivity in the pyrolysis of all studied binary mixtures, indicating the existence of obvious synergistic effects. In particular, such effects become more remarkable when increasing the initial acetylene concentration. This essentially results from the addition-elimination reaction of a toluene fuel radical and a C 2 fuel molecule leading to a C 9 molecule and a hydrogen atom. Indene is identified as the predominant C 9 product in all studied cases, and its peak concentrations sharply increase with the initial acetylene contents in toluene-acetylene pyrolysis. On the other hand, indane, produced from the addition-elimination reaction between benzyl and ethylene, is only detected at trace levels in toluene/ethylene pyrolysis. This indicates a relatively weaker interaction between benzyl and ethylene, compared to that of benzyl and acetylene. Apart from the increased concentrations of hydrogen atoms and C 9 aromatics, interactions between toluene and C 2 fuels also directly result in a reduced level of C 7 radicals in the reaction system. Overall, PAH species can be divided into two groups according to the way their peak concentrations varying with the initial fuel compositions. For those largely depending on benzyl reactions, such as bibenzyl, biphenylmethane, fluorene and phenanthrene, the peak concentrations decrease with the added C 2 fuels. In contrast, increasing trends are observed in the peak concentrations of the PAHs which rely on indenyl as a precursor, including naphthalene, methyl-indene, benzofulvene and acenaphthalene. [ABSTRACT FROM AUTHOR]

This work presents a comparative study on the pyrolysis of C 8 –C 10 linear alkylbenzenes including ethylbenzene, n -propylbenzene and n -butylbenzene. Experiments were performed with highly diluted mixtures in argon containing respectively the three fuels under nearly identical conditions in a single-pulse shock tube, at a nominal pressure of 20 bar and over a temperature range of 950–1700 K. Post-shock gas mixtures were sampled and analyzed with the gas chromatographic technique so that species concentration evolutions as function of temperature were obtained for the pyrolysis of each fuel. A kinetic model was developed to interpret the similarities and differences regarding the fuel decomposition and species formation behaviors observed in the experiments. The fuel conversion of n -propylbenzene and n -butylbenzene proceeds along a similar curve, which is much faster than that of ethylbenzene. All three fuels are consumed mainly through the bond fission producing benzyl radical. The simultaneously formed C 1 –C 3 alkyl radicals in separate cases significantly impact the fuel reactivity and the formation of small C 1 –C 4 and monocyclic aromatic hydrocarbons. Specifically, in n -propylbenzene pyrolysis, the decomposition of ethyl radicals produces a considerable amount of hydrogen atoms, which enhances the reactivity of the reaction system and meanwhile results in relatively high production of benzene during the fuel consumption. The formation of other monocyclic aromatic hydrocarbon intermediates, such as toluene and styrene, is also influenced by fuel-related pathways. Concerning PAH formation, the kinetic schemes in the pyrolysis of linear C 8 –C 10 alkylbenzenes are very similar, which are dominated by the reactions of benzyl and other resonantly-stabilized radicals produced from benzyl decomposition. The major PAH formation reactions are barely influenced by the fuel chemistry. The only notable fuel-specific pathway is the indene formation from 1-phenyl-2-propenyl in n -propylbenzene and n -butylbenzene pyrolysis at relatively low temperatures. Styrene is an abundant product and its reaction with phenyl is found to be an important channel of phenanthrene formation. [ABSTRACT FROM AUTHOR]

Pyrolysis of phenylacetylene with and without the presence of C 2 hydrocarbons (acetylene or ethylene) was studied in a single-pulse shock tube coupled to gas chromatography/gas chromatography-mass spectrometry equipment for speciation diagnostics. Quantitative speciation profiles were probed from each reaction system over the temperature range of 1100–1700 K at a nominal pressure of 20 bar. A kinetic model was proposed to interpret how phenylacetylene is consumed under high-pressure pyrolytic conditions and how the resulting intermediates react to form polycyclic aromatic hydrocarbons (PAHs), and furthermore, how the extra acetylene or ethylene alter the reaction schemes. It was found that the bimolecular reaction between phenylacetylene and hydrogen atom leading to phenyl and acetylene dominates phenylacetylene decomposition throughout the temperature window. The addition/elimination reactions between phenylacetylene and phenyl not only produce hydrogen atoms to maintain the reactivity of the fuel decay, but also directly lead to the formation of several C 14 H 10 PAH isomers including diphenylacetylene, 9-methylene-fluorene and phenanthrene. Intermediates pools, regarding both species categories and abundance, are changed by the two C 2 fuels introduced into the reaction system. The added acetylene enables the Hydrogen-Abstraction-Acetylene-Addition (HACA) mechanism starting from the phenylacetylene radical to occur at relatively low temperatures. But the yielded naphthyl core does not stabilize in naphthalene due to the lack of hydrogen atoms in the reaction system, and instead, it carries on the HACA route by further combining with another acetylene molecule, ending up in acenaphthylene. Differently, the added ethylene intensifies the HACA routes by contributing to the acetylene formation, and more importantly, provides hydrogen atoms participating in the naphthalene formation from naphthyl radical. [ABSTRACT FROM AUTHOR]

This work reports a kinetic study on the pyrolysis of three xylene isomers based on single-pulse shock tube experiments and detailed kinetic modeling. Speciation measurements for the post-shock gas mixtures are obtained via sampling and gas-chromatography-mass spectrometry over a temperature range of 1150−1650 K at a nominal pressure of 20 bar. A sub-mechanism incorporating consumption reactions of xylene isomers as well as subsequent pathways leading to polycyclic aromatic hydrocarbons (PAHs) is developed and integrated into our on-going PAH formation kinetic model. The model can satisfactorily predict the qualitative measurements and accurately characterize both the similarities and fuel-specific features in the pyrolysis of three xylenes. The three isomers decompose at similar rates, though m-xylene exhibits a slightly weaker reactivity. This arises from the fact that m-xylyl, different from its o- and p- counterparts, cannot undergo hydrogen loss to form m-xylylene diradical. Distinct consumption schemes of the three xylyl radicals also result in the different species pools observed at temperatures below 1400 K. A large amount of styrene results from a stepwise isomerization of o-xylylene following dehydrogenation of o-xylyl. An early formation of anthracene is noted as a unique phenomenon in o-xylene pyrolysis, which is attributed to specific reactions of o-xylyl. Due to a relatively high abundance of m-xylyl, the self-recombination product 3,3′-dimethylbibenzyl is among the major species formed at the initial stage of m-xylene pyrolysis. p-Xylyl predominantly converts to p-xylylene which is largely consumed via polymerization processes. Besides, mutual conversions among the three xylyl radicals are found to play an essential role in the pyrolysis of three xylenes. Toluene is measured of significant concentrations in the pyrolysis of all three isomers, which rationalizes that PAH speciation in the pyrolysis of three xylenes and toluene is highly similar at elevated temperatures. Modeling analyses show that apart from the benzyl/toluene chemistry, reactions involving C 8 species also have important contributions to PAH formation in xylenes pyrolysis. [ABSTRACT FROM AUTHOR]

A combined experimental and kinetic modeling study is carried out to explore the influences of added acetylene, ethylene, propylene, and propyne on the reaction schemes of benzene pyrolysis. Pyrolysis of benzene with and without the presence of the C 2 - or C 3 - unsaturated hydrocarbons (HCs) is conducted in a single pulse shock tube coupled to gas chromatography-mass spectrometry technique. A minimum of 30 species is detected in each reaction system, and their mole fraction profiles are obtained over the temperature range 1030–1800 K at a nominal pressure of 20 bar and a nominal reaction time of 4 ms. With updates based on recent theoretical studies, our ongoing detailed kinetic model with 552 species and 4958 reactions can successfully reproduce the decomposition reactivity of the fuels, formation of decomposition products, and the growth of aromatics in the pyrolysis of different fuel mixtures. Various considerations apply to all studied binary mixtures. The addition of C 2 - and C 3 - HCs to the reaction system leads to C 2 H 2 formation, and consequently promotes the HACA mechanism starting from phenyl radical (C 6 H 5) at relatively low temperatures. The resulted phenylacetylene, formed through C 6 H 5 +C 2 H 2 reaction, promotes the addition-elimination reaction C 6 H 5 C 2 H + C 6 H 5 leading to the enhanced and early formation of all C 14 H 10 PAH isomers including ethynyl biphenyl, methylene-fluorene, diphenylacetylene, phenanthrene, and anthracene. It is also noteworthy that the existence of C 2 H 2 as fuel or its production from C 2 H 4 , C 3 H 6 , and C 3 H 4 -P decomposition results in numerous compounds with ethynyl branches such as ethynyl biphenyl, diethynyl naphthalene, and ethynyl acenaphthylene. Considering the specific features of the different fuel mixtures, the addition of acetylene intensifies the HACA route leading to greater acenaphthylene formation, while naphthalene formation remains similar to the pure benzene case due to the limited H-atoms. Differently, in benzene-C 2 H 4 co-pyrolysis, naphthalene and acenaphthylene are mainly formed through reactions between PAH radicals (phenylacetylene radical and naphthyl radical, respectively) and ethylene. Concerning benzene-C 3 co-pyrolysis, indene is the major C 9 species resulting from the reaction of benzene/phenyl with C 3 fuels. This is an important theoretical pathway to indene which is experimentally probed here for the first time. The high concentration of indene leads to the enhanced formation of naphthalene and acenaphthylene through the reactions of indenyl radical with methyl and propargyl (C 3 H 3) radicals, respectively. Afterwards, the naphthyl radicals participate in the formation of several larger C11–13 PAHs such as methylnaphthalene, ethynylnaphthalene and fluorene through their reactions with CH 3 , C 2 H 2 and C 3 H 4 -P/C 3 H 3 , respectively. [ABSTRACT FROM AUTHOR]

To explore the potential interactions between toluene/benzyl and the common C 3 combustion intermediates, toluene-propylene and toluene-propyne co-pyrolysis is studied in the current work by taking neat toluene pyrolysis as a reference. Experiments are carried out at a nominal pressure of 20 bar over a temperature range of 1050−1700 K, using a single-pulse shock tube facility coupled to the gas chromatography-mass spectrometry speciation diagnostic technique. Temperature-dependent mole fraction profiles are obtained for numerous species ranging from small-molecule products to three-ring polycyclic aromatic hydrocarbons (PAHs). A kinetic model, which has been under development in our serial works, is extended by including the interplays between toluene/benzyl and propylene/propyne chemistry. The updated model can satisfactorily predict the measurements, regarding the absolute mole fractions as well as the variation trends brought by different initial fuel compositions. Increased reactivity is observed in the conversion of toluene with the presence of propylene or propyne, while the consumption rates of the studied C 3 fuels are barely influenced by toluene. Benzene formation is facilitated by the C 3 +C 3 reactions introduced by the C 3 fuels. The pyrolysis of propylene (or propyne) significantly enhances the level of C 1 −C 3 molecules/radicals that further react with aromatic species. For instance, the reactions of benzyl+propyne result in much higher mole fractions and lower speciation temperature windows of indene and naphthalene in toluene-propylene (or propyne) co-pyrolysis. The reactions with small hydrocarbons result in reduced levels of benzyl and other C 7 radicals in the reaction system in toluene- propylene (or propyne) co-pyrolysis. Consequently, for the PAHs which are mainly formed through C 7 +C 7 reactions, such as bibenzyl and phenanthrene, the mole fractions are lowered by the addition of propylene (or propyne). Propyne has more obvious influences on the species pool of toluene pyrolysis than propylene, because the effective C 7 C 3 interactions are mostly through the reactions between toluene/benzyl and propyne/propargyl in both cases of toluene-propylene and toluene-propyne co-pyrolysis. [ABSTRACT FROM AUTHOR]

This work is centered on the speciation from propylene and propyne pyrolysis by means of shock tube experiments and detailed kinetic modeling. A wealth of intermediates and products, covering small acyclic hydrocarbons up to four-ring aromatics, are probed from the C 3 fuels pyrolysis at a nominal pressure of 20 bar over 1050–1650 K. With updates in reactions involving C 3 species, our on-going polycyclic aromatic hydrocarbon (PAH) formation kinetic model can well predict the measurements obtained in the current work as well as relevant literature data. Propyne exhibits a unique two-stage decomposition profile, as the characteristic isomerization to allene dominates in its consumption at moderate temperatures below 1300 K. Overall, propylene pyrolysis results in more diverse small hydrocarbons, but much lower contents of aromatics, in comparison to propyne pyrolysis. In both studied cases, the formation of benzene is dependent upon the propargyl recombination, and since propyne decomposition induces a more rapid and more plentiful propargyl production, benzene mole fractions are much higher in propyne pyrolysis. In both cases, naphthalene is observed as the most abundant PAH species, followed by acenaphthalene. Modeling analyses indicate that similar reaction pathways are responsible for the PAH formation in propylene and propyne pyrolysis. Indene is formed from the interactions between benzene/phenyl and C 3 species, through its non-PAH isomers as intermediates. The subsequent reactions of indenyl radical with methyl and propargyl are essential pathways leading to naphthalene and acenaphthalene, respectively. Naphthyl radical further participates in the formation of different larger PAHs. The methylene-substituted cyclopenta-ring species are deemed as important precursors of their aromatic isomers, as is noted from the fulvene-to-benzene, benzofulvene-to-naphthalene and 9-methylene-fluorene-to-phenanthrene conversions. [ABSTRACT FROM AUTHOR]