High Temperature Reactions of CH<sub>3</sub> 2. H‐Abstraction from Alkanes

Möller, W.; Mozzhukhin, E. V.; Wagner, H. Gg.

doi:10.1002/bbpc.19870910615

Cited by 20 publications

(35 citation statements)

References 42 publications

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“…At high temperatures, the only inconsistent data are the rate constants of Møller et al 72 for CH 3 + ethane, obtained using optical absorption techniques for methyl radicals. These appear to be too large and are in poor agreement with the other data.…”

Section: Articlementioning

confidence: 93%

Evaluated Kinetics of the Reactions of H and CH₃ with n-Alkanes: Experiments with n-Butane and a Combustion Model Reaction Network Analysis

2015

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Presented is a combined experimental and modeling study of the kinetics of the reactions of H and CH3 with n-butane, a representative aliphatic fuel. Abstraction of H from n-alkane fuels creates alkyl radicals that rapidly decompose at high temperatures to alkenes and daughter radicals. In combustion and pyrolysis, the branching ratio for attack on primary and secondary hydrogens is a key determinant of the initial olefin and radical pool, and results propagate through the chemistry of ignition, combustion, and byproduct formation. Experiments to determine relative and absolute rate constants for attack of H and CH3 have been carried out in a shock tube between 859 and 1136 K for methyl radicals and 890 to 1146 K for H atoms. Pressures ranged from 140 to 410 kPa. Appropriate precursors are used to thermally generate H and CH3 in separate experiments under dilute and well-defined conditions. A mathematical design algorithm has been applied to select the optimum experimental conditions. In conjunction with postshock product analyses, a network analysis based on the detailed chemical kinetic combustion model JetSurf 2 has been applied. Polynomial chaos expansion techniques and Monte Carlo methods are used to analyze the data and assess uncertainties. The present results provide the first experimental measurements of the branching ratios for attack of H and CH3 on primary and secondary hydrogens at temperatures near 1000 K. Results from the literature are reviewed and combined with the present data to generate evaluated rate expressions for attack on n-butane covering 300 to 2000 K for H atoms and 400 to 2000 K for methyl radicals. Values for generic n-alkanes and related hydrocarbons are also recommended. The present experiments and network analysis further demonstrate that the C-H bond scission channels in butyl radicals are an order of magnitude less important than currently indicated by JetSurf 2. Updated rate expressions for butyl radical fragmentation reactions are provided.

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Section: Articlementioning

confidence: 93%

Evaluated Kinetics of the Reactions of H and CH₃ with n-Alkanes: Experiments with n-Butane and a Combustion Model Reaction Network Analysis

2015

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“…The following reaction steps are dominated by oxygen addition, to form oxygenated species like alcohols, aldehydes, ethers etc., and further decomposition steps like abstraction of H atoms or hydrocarbons. H-abstraction reactions of different hydrocarbons were the focus of several theoretical [5][6][7][8][9][10] and experimental studies [11][12][13][14][15][16][17][18]. Khaled et al have investigated the reactions of linear alkenes [11] and i-butene [12] with OH radicals in shock tubes and showed that the reaction rate coefficients are dependent on the chain length and the position of the double bond, that is, the constitutional isomer.…”

Section: Introductionmentioning

confidence: 99%

“…Manion et al [16] investigated H-abstraction reactions of n-alkanes by H and CH 3 radicals and showed a strong temperature dependence of the ratio between primary and secondary H-abstractions. The Habstraction by CH 3 radicals from ethane was the target of the investigations by Möller et al [17], while the decomposition of butane isomers by H radicals was investigated by Peukert et al [18] in a shock tube study.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen abstraction ratios: A systematic iPEPICO spectroscopic investigation in laminar flames

Krüger

Oßwald

Köhler

et al. 2018

Combustion and Flame

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The radicals produced by hydrogen abstraction in the initial fuel decomposition step are essential in combustion kinetics, but their experimental detection is very challenging. Imaging photoelectron photoion coincidence spectroscopy enables the detection and identification of even these isomeric radicals. Laminar low-pressure (40 mbar) hydrogen flames doped with different alkanes and alkenes are investigated systematically with the goal to identify the formation pathways and the fate of fuel radicals formed in hydrogen abstraction reactions. The abstraction reactions of primary, secondary, tertiary, and vinylic H atoms were never target of a systematic, direct semiquantitative investigation in a flame environment and this paper describes such a study for the first time. Performing the measurements at the vacuum ultraviolet beamline located at the Swiss Light Source enables isomer-selective detection of reactive radical species by imaging photoelectron photoion coincidence spectroscopy. For unambiguous identification of several isomeric radicals, threshold photoelectron spectra were compared with reference photoelectron spectra. H-abstraction ratios of isomeric radicals were determined and compared to literature reaction barriers and rate coefficients. In addition to the quantitative information, the peak positions of the profiles of radicals formed by hydrogen abstraction or addition to the fuel molecules as function of distance from the burner show faster H-abstraction for unbranched alkanes and alkenes than for branched fuels and faster H-addition than H-abstraction, respectively. 1

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“…5) together with the rate constants of the reactions mentioned (5, 15,45). The data for the reaction CH3 + CH4 have been calculated from preliminary measurements of CH3 + CD4 [13].…”

Section: Several Experimental Studies Have Been Devoted To the Kinetimentioning

confidence: 99%

An investigation of the reaction between CH₃ radicals and methanol at high temperatures

Dombrowsky

Wagner

1989

Ber Bunsenges Phys Chem

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Chemical Kinetics J Elementary Reactions J Radicals J Shock WavesThe reaction of methyl radicals with methanol was investigated behind incident shock waves at temperatures between 1200 and 1400 K.The kinetic data were obtained from time resolved absorption measurements of CH3 at the wavelength A = 216.5 nm. The results suggest a curved Arrhenius plot, which can be extrapolated to real flame conditions. A comparison with other methyl radical reactions shows coherence in the temperature dependence of the rate coefficients.

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High Temperature Reactions of CH₃ 2. H‐Abstraction from Alkanes

Abstract: Thc rate coefficients of the reactions CH, + C& -+ CH4 + C2Hs (1) and CH3 + CD4 .--t CD4 -+ CH3D + CD3 (2) were determined at high temperatures behind incident shock waves by time-resolved measurements of the absorption of the methyl radical at 216.5 nm. The resulting Arrhenius expressions

Cited by 20 publications

References 42 publications

Evaluated Kinetics of the Reactions of H and CH₃ with n-Alkanes: Experiments with n-Butane and a Combustion Model Reaction Network Analysis

Evaluated Kinetics of the Reactions of H and CH₃ with n-Alkanes: Experiments with n-Butane and a Combustion Model Reaction Network Analysis

Hydrogen abstraction ratios: A systematic iPEPICO spectroscopic investigation in laminar flames

An investigation of the reaction between CH₃ radicals and methanol at high temperatures

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High Temperature Reactions of CH3 2. H‐Abstraction from Alkanes

Cited by 20 publications

References 42 publications

Evaluated Kinetics of the Reactions of H and CH3 with n-Alkanes: Experiments with n-Butane and a Combustion Model Reaction Network Analysis

Evaluated Kinetics of the Reactions of H and CH3 with n-Alkanes: Experiments with n-Butane and a Combustion Model Reaction Network Analysis

Hydrogen abstraction ratios: A systematic iPEPICO spectroscopic investigation in laminar flames

An investigation of the reaction between CH3 radicals and methanol at high temperatures

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High Temperature Reactions of CH₃ 2. H‐Abstraction from Alkanes

Evaluated Kinetics of the Reactions of H and CH₃ with n-Alkanes: Experiments with n-Butane and a Combustion Model Reaction Network Analysis

Evaluated Kinetics of the Reactions of H and CH₃ with n-Alkanes: Experiments with n-Butane and a Combustion Model Reaction Network Analysis

An investigation of the reaction between CH₃ radicals and methanol at high temperatures