Shock tube studies of gas phase reactions preceding the soot formation process

Kern, R. D.; Xie, Kexin

doi:10.1016/0360-1285(91)90010-k

Cited by 79 publications

(46 citation statements)

References 118 publications

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“…The mechanism of soot formation is highly complex and involves a large number of chemical and physical processes (Glassman 1989;Kern and Xie 1991;Mansurov 2005). In a shock tube, the high temperature behind the reflected shock wave initiates the pyrolysis of propane, producing small radicals which react to form acetylene, benzene, naphthalene, and increasingly large PAH.…”

Section: Discussionmentioning

confidence: 99%

“…Because of these advantages, shock tubes have been extensively used to study the reaction chemistry preceding the inception of soot (Kern and Xie 1991), the formation of soot upon combustion of saturated, unsaturated, and aromatic hydrocarbons (Frenklach et al 1983;Kellerer et al 1996;Agafonov et al 2011), and also the effects of various additives, such as oxygenated organics or ceria oxide nanoparticles on the soot yield (Alexiou and Williams 1996;Hong et al 2009;Rotavera et al 2009). Although the laser light extinction and scattering diagnostics can be used to quantify the minute and time-dependent details of the soot generation process, such as the growth of primary soot spherules (Kellerer et al 1996), it is often not possible to observe late processes, such as coagulation and condensation, which may significantly change the chemical composition, mixing state, and morphology of particles when soot in the test section of the shock tube is cooled by the driver gas.…”

Section: Introductionmentioning

confidence: 99%

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Characterization of Soot Aerosol Produced from Combustion of Propane in a Shock Tube

Khalizov¹,

Hogan²,

Qiu³

et al. 2012

Aerosol Science and Technology

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The knowledge of yields and properties of soot from combustion of hydrocarbon fuels is crucial for accurate evaluation of the impacts of primary aerosols on air quality and climate. This study presents measurements of soot generated from combustion of propane in a shock tube, using independently adjustable fuel equivalence ratio (φ), temperature, and pressure. The characterization of soot yields inside the shock tube by in situ laser extinction is complemented with a set of comprehensive measurements of soot transferred into a fluoropolymer chamber, including particle size distributions, elemental carbon (EC) mass fraction, effective density, mass fractal dimension (Dfm), dynamic shape factor (χ ), and optical properties. The properties of soot particles and the soot yield are sensitive to combustion conditions and the duration of the combustion experiment. High-temperature combustion with φ = 2.5 produces small fractal (Dfm = 2) soot particles composed mainly of EC (up to 90%), at a low mass yield. Particles from lower temperature combustion contain a significant fraction of organic material (∼50%). Using rich fuel mixtures (φ = 4.0 and 8.0) significantly increases particle size and soot mass yield. At lower temperatures, compact (Dfm = 3) and nearly spherical (χ = 1.1) aggregates with high organic content are formed, whereas at higher temperatures, the particles are fractal and closely resemble those obtained using φ = 2.5. Single scattering albedo (SSA) varies from 0.15 for fractal particles to 0.75 for compact particles. For soot generated at high equivalence ratios, SSA can be used as a proxy for particle morphology and EC content.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Characterization of Soot Aerosol Produced from Combustion of Propane in a Shock Tube

Khalizov¹,

Hogan²,

Qiu³

et al. 2012

Aerosol Science and Technology

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“…This mechanism applies to a much wider range of reactants and products, but is much slower than six-center isomerization, since it requires formation of a biradical. (The available six-center isomerization Arrhenius parameters [34,36] predict rates in our temperature regime that are roughly 100 times higher than those for carbene isomerizations [25,40,41].) Presumably carbene isomerizations are important for propadiene and 1,3-butadiene because all of their C-C bonds are double or vinylic, so their C-C fission rates are very low.…”

Section: The Role Of Isomerizationmentioning

confidence: 94%

Decomposition and hydrocarbon growth processes for hexadienes in nonpremixed flames

McEnally¹,

Pfefferle²

2008

Combustion and Flame

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Alkadienes are formed during the decomposition of alkanes and play a key role in the formation of aromatics due to their degree of unsaturation. The experiments in this paper examined the decomposition and hydrocarbon growth mechanisms of a wide range of hexadiene isomers in soot-forming nonpremixed flames. Specifically, C3 to C12 hydrocarbon concentrations were measured on the centerlines of atmospheric-pressure methane/air coflowing nonpremixed flames doped with 2000 ppm of 1,3-, 1,4-, 1,5-, and 2,4-hexadiene and 2-methyl-1,3-, 3-methyl-1,3-, 2-methyl-1,4-, 3-methyl-1,4-pentadiene, and 2,3-dimethyl-1,3-butadiene. The hexadiene decomposition rates and hydrocarbon product concentrations showed that the primary decomposition mechanism was unimolecular fission of C-C single bonds, whose fission produced allyl and other resonantly stabilized products. The one isomer that does not contain any of these bonds, 2,4-hexadiene, isomerized by a six-center mechanism to 1,3-hexadiene. These decomposition pathways differ from those that have been observed previously for propadiene and 1,3-butadiene, and these differences affect aromatic hydrocarbon formation. 1,5-Hexadiene and 2,3-dimethyl-1,3-butadiene produced significantly more C 3 H 4 and C 4 H 4 than the other isomers, but less benzene, which suggests that benzene formation pathways other than the conventional C3 + C3 and C4 + C2 pathways were important in most of the hexadiene-doped flames. The most likely additional mechanism is cyclization of highly unsaturated C5 decomposition products, followed by methyl addition to cyclopentadienyl radicals.

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“…The CAH bonds in benzene are weaker than the CAC bond in the ring [61]. Thus, the initiation step in benzene pyrolysis is the release of a hydrogen atom by breaking one of the CAH bonds in the molecule.…”

Section: Shock Tube Experiments Of Benzene Pyrolysismentioning

confidence: 98%