Uniqueness in the low temperature oxidation of cycloalkanes

Journal Article · Wed Dec 15 04:00:00 EST 2010 · Combustion and Flame

DOI:https://doi.org/10.1016/J.COMBUSTFLAME.2010.06.005· OSTI ID:21390739

Yang, Yi; Boehman, Andre L ^[1]; Simmie, John M ^[2]

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1. EMS Energy Institute, The Pennsylvania State University, University Park, PA 16802 (United States)
2. Combustion Chemistry Center, National University of Ireland, Galway (Ireland)

This work examines the inherent features in the low temperature oxidation of cycloalkanes which distinguish cyclic alkanes from open-chain alkanes. The first part of the discussion is based on the recent motored-engine studies of cyclic hydrocarbons, [Yang and Boehman, Proc. Combust. Inst. 32, p. 419; Yang and Boehman, Combust. Flame, 157, p. 495], and focuses on the formation of conjugate olefins in low temperature oxidation. While less reactive than linear alkanes of similar size, cyclic hydrocarbons produced significant amounts of conjugate olefins during low temperature oxidation, which is uncharacteristic of linear alkanes. Conformational analyses in this paper and in a companion paper reveal that the inhibited low temperature chain branching and the promoted olefin formation are due to the steric structures of the cyclic compounds limiting the number of hydrogens available to the (1,5) H-shift but alternatively enhancing the opportunity for the (1,4) H-shift during the isomerization of the fuel peroxy radicals, ROO{sup .}{yields}{sup .}QOOH. The second part of this work focuses on the role of methyl substitution in low temperature oxidation of cycloalkanes, which is drastically different from that of linear alkanes. Ab initio calculations are conducted on cyclohexane and methylcyclohexane to compute the activation energy of the (1,5) and (1,4) H-shift with full consideration of species conformation. The presence of the methyl group is found to enable low activation-energy channels in the (1,5) H-shift. Next, the impact of methyl substitution on the formation of conjugate olefins is discussed for methylcyclohexane and methylcyclopentane. Based on the experimentally determined yields of conjugate olefin isomers, estimations are made of the fraction of each fuel radical that is converted to conjugate olefins. For both compounds, more tertiary radicals are converted to conjugate olefins than secondary radicals, and primary radicals have the least fraction being converted. (author)

• OSTI ID: 21390739
• Journal Information: Combustion and Flame, Journal Name: Combustion and Flame Journal Issue: 12 Vol. 157; ISSN CBFMAO; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ACTIVATION ENERGY
ALKENES
Ab initio calculations
CYCLOALKANES
CYCLOHEXANE
Conjugate olefins
Cycloalkanes
Degenerate chain branching
HYDROGEN
ISOMERIZATION
ISOMERS
Internal hydrogen abstraction
Low temperature oxidation
OXIDATION
PEROXY RADICALS
TEMPERATURE RANGE 0400-1000 K
YIELDS