Decomposition and hydrocarbon growth processes for hexadienes in nonpremixed flames

Journal Article · Sat Mar 15 04:00:00 EDT 2008 · Combustion and Flame

DOI:https://doi.org/10.1016/J.COMBUSTFLAME.2007.11.003· OSTI ID:21030264

McEnally, Charles S; Pfefferle, Lisa D ^[1]

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1. Department of Chemical Engineering and Center for Combustion Studies, Yale University, New Haven, CT 06520-8286 (United States)

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{sub 3}H{sub 4} and C{sub 4}H{sub 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. (author)

• OSTI ID: 21030264
• Journal Information: Combustion and Flame, Journal Name: Combustion and Flame Journal Issue: 4 Vol. 152; ISSN CBFMAO; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
AIR
ALLENE
ATMOSPHERIC PRESSURE
BENZENE
BUTADIENE
COMBUSTION
COMBUSTION KINETICS
CYCLIZATION
DECOMPOSITION
DIENES
FLAMES
METHANE
PARTICULATES
RADICALS
SOOT