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Title: Chemical structures of low-pressure premixed methylcyclohexane flames as benchmarks for the development of a predictive combustion chemistry model

The chemical compositions of three low-pressure premixed flames of methylcyclohexane (MCH) are investigated with the emphasis on the chemistry of MCH decomposition and the formation of aromatic species, including benzene and toluene. The flames are stabilized on a flat-flame (McKenna type) burner at equivalence ratios of φ = 1.0, 1.75, and 1.9 and at low pressures between 15 Torr (= 20 mbar) and 30 Torr (= 40 mbar). The complex chemistry of MCH consumption is illustrated in the experimental identification of several C7H12, C7H10, C6H12, and C6H10 isomers sampled from the flames as a function of distance from the burner. Three initiation steps for MCH consumption are discussed: ring-opening to heptenes and methyl-hexenes (isomerization), methyl radical loss yielding the cyclohexyl radical (dissociation), and H abstraction from MCH. Mole fraction profiles as a function of distance from the burner for the C7 species supplemented by theoretical calculations are presented, indicating that flame structures resulting in steeper temperature gradients and/or greater peak temperatures can lead to a relative increase in MCH consumption through the dissociation and isomerization channels. Trends observed among the stable C6 species as well as 1,3-pentadiene and isoprene also support this conclusion. Relatively large amounts of toluene and benzenemore » are observed in the experiments, illustrating the importance of sequential H-abstraction steps from MCH to toluene and from cyclohexyl to benzene. Furthermore, modeled results using the detailed chemical model of Pitz et al. (Proc. Combust. Inst.2007, 31, 267–275) are also provided to illustrate the use of these data as a benchmark for the improvement or future development of a MCH mechanism.« less
Authors:
 [1] ;  [2] ;  [1] ;  [3] ;  [1]
  1. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  2. Princeton Univ., Princeton, NJ (United States)
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
OSTI Identifier:
1281677
Report Number(s):
LLNL-JRNL--519712
Journal ID: ISSN 0887-0624
Grant/Contract Number:
AC52-07NA27344
Type:
Accepted Manuscript
Journal Name:
Energy and Fuels
Additional Journal Information:
Journal Volume: 25; Journal Issue: 12; Journal ID: ISSN 0887-0624
Publisher:
American Chemical Society (ACS)
Research Org:
Lawrence Livermore National Lab., Livermore, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
30 DIRECT ENERGY CONVERSION; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY cycloalkane; flame-sampling; molecular beam; mass-spectrometry; methylcyclohexane; premixed flames; low-pressure flames; polycyclic aromatic hydrocarbon