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A combined experimental and kinetic modeling study is presented to improve the understanding of the formation of polycyclic aromatic hydrocarbons (PAHs) from neat cyclopentene and cyclopentene/acetylene mixtures. High-pressure experiments are conducted for the first time over a temperature range covering 930–1650 K using a single-pulse shock tube coupled to gas chromatography/gas chromatography-mass spectrometry (GC/GC–MS) techniques. Several updates and inclusions, mainly regarding the reactions involving C 5 molecules and radicals, are made in our on-going PAH kinetic model, which shows satisfactory predictive performances for the speciation measurements obtained in the current work and in the literature. On the basis of the experimental observations and modeling analyses, the reaction pathways active during the pyrolysis of cyclopentene are illustrated and the effects of acetylene addition as co-reactant on the PAH chemistry are assessed. In all of the cases investigated, it is noted that the cyclopentadienyl radical largely participate in the formation of mono-aromatic hydrocarbons (benzene and styrene) and PAHs (indene, naphthalene and phenanthrene). [ABSTRACT FROM AUTHOR]

Benzene and toluene were pyrolyzed under highly argon-diluted conditions at a nominal pressure of 20 bar in a single-pulse shock tube coupled to gas chromatography/gas chromatography–mass spectrometry (GC/GC–MS) diagnostics. Concentration evolutions of polycyclic aromatic hydrocarbon (PAH) intermediates were measured in a temperature range of 1100–1800 K by analyzing the post-shock gas mixtures. Different PAH speciation behaviors, regarding types, concentrations and formation temperature windows, were observed in the two reaction systems. A kinetic model was proposed to predict and interpret the measurements. Through a combination of experimental and modeling efforts, PAH formation patterns from species pools of benzene and toluene pyrolysis were illustrated. In both cases, channels leading to PAHs basically originate from the respective fuel radicals, phenyl and benzyl. Due to the higher thermal stability of benzene, the production of phenyl, and thus most PAH species, occur in higher temperature windows, in comparison to the case of toluene. In benzene pyrolysis, benzyne participates in the formation of crucial PAH species such as naphthalene and acenaphthylene. Phenyl self-recombination takes considerable carbon flux into biphenyl, which serves as an important intermediate leading to acenaphthylene through hydrogen loss and ring closure. The resonantly-stabilized benzyl is abundant in toluene pyrolysis, and its decomposition further produces other resonantly-stabilized radicals such as fulvenallenyl and propargyl. Barrierless addition reactions among these radicals are found to be important sources of PAHs. Fuel-specific pathways have pronounced effects on PAH speciation behaviors, particularly at lower temperatures where fuel depletion is not completed within the reaction time of 4.0 ms. Contributions from the commonly existing Hydrogen-Abstraction-Carbon-Addition (HACA) routes increase with the temperature in both cases. [ABSTRACT FROM AUTHOR]

Styrene is an important compound for polymer production and a key intermediate in gas-phase kinetics of polycyclic aromatic hydrocarbons (PAHs). For the first time, the pyrolysis of styrene with and without the presence of acetylene is investigated in a single-pulse shock tube coupled to gas chromatography and mass spectrometry. For each reaction system, quantitative speciation profiles are probed within the temperature range of 1100–1730 K, nominal pressure of 20 bar, and reaction duration of ∼ 4 ms. A kinetic model is built to simulate the results. The model explains how styrene is consumed under high-pressure pyrolytic conditions, how the secondary chemistry of intermediate products affect subsequent PAH formation, and how acetylene addition alters the reaction pathways. Throughout the temperature range, styrene breakdown is dominated by the bimolecular interaction between styrene and hydrogen atom, which produces benzene+vinyl or phenyl and ethylene through the stabilization of 2-phenylethyl and its subsequent dissociation. As a result, large amounts of phenyl accumulate, which react with styrene to form C 14 H 12 species while simultaneously releasing H atoms through addition/elimination reactions. The reactivity of fuel consumption is preserved by the regeneration of H atoms as chain carriers. Several C 14 H 10 compounds are formed as a result of the following breakdown of the C 14 H 12 isomers, particularly stilbene, 1,1-diphenyl ethylene, and 9-methyl-9H-fluorene. The presence of acetylene as a co-reactant with styrene allows the Hydrogen-Abstraction-Acetylene-Addition (HACA) pathway to proceed from phenyl radical to enhance the production of phenylacetylene at very low temperatures and acenaphthylene. This hinders the formation of C 14 H 12 isomers, exclusive products from pure styrene dissociation by competing with the styrene+phenyl routes. [ABSTRACT FROM AUTHOR]

Abstract: High pressure iso-octane shock tube experiments were conducted to assist in the development of a Jet A surrogate kinetic model. Jet A is a kerosene based jet fuel composed of hundreds of hydrocarbons consisting of paraffins, olefins, aromatics and naphthenes. In the formulation of the surrogate mixture, iso-octane represents the branched paraffin class of hydrocarbons present in aviation fuels like Jet A. The experimental work on iso-octane was performed in a heated high pressure single pulse shock tube. The mole fractions of the stable species were determined using gas chromatography and mass spectroscopy. Experimental data on iso-octane oxidation and pyrolysis were obtained for temperatures from 835 to 1757K, pressures from 21 to 65atm, reactions times from 1.11 to 3.66ms, and equivalence ratios from 0.52 to 1.68, and ∞. Iso-octane oxidation showed that the fuel decays through thermally driven oxygen free decomposition at conditions studied. This observation prompted an experimental and modeling study of iso-octane pyrolysis using an iso-octane sub-model taken from a recently published n-decane/iso-octane/toluene surrogate model. The revised iso-octane sub-model showed improvements in predicting intermediate species profiles from pyrolytic experiments and oxidation experiments. The modifications to the iso-octane sub-model also contributed to better agreement in predicting the formation of carbon monoxide and carbon dioxide when compared to the recently published 1st Generation Surrogate model and a recently published iso-octane oxidation model. Model improvements were also seen in predicting species profiles from flow reactor oxidation experiments and ignition delay times at temperatures above 1000K at both 10 and 50atm. [Copyright &y& Elsevier]