Experimental and modeling study of the effects of adding oxygenated fuels to premixed n-heptane flames

Gen Chen, Wu Yu, Jin Fu, Jun Mo, Zuohua Huang*, Jiuzhong Yang, Zhandong Wang, Hanfeng Jin, Fei Qi

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

67 Scopus citations

Abstract

The effects of methanol, dimethoxymethane (DMM), and dimethylcarbonate (DMC) on laminar premixed low pressure (30Torr) n-heptane flames were investigated by using synchrotron photoionization and molecular-beam mass spectrometry (PI-MBMS) techniques. The overall C/O ratio was maintained constant (0.507) and the equivalence ratio was kept around 1.6 for all the tested flames. The composition of unburned mixtures was adjusted such that the post-flame temperatures were nearly equivalent for all the test conditions. Mole fraction profiles of major and intermediate species were derived and compared among the flames. Parallel computations were performed based on a modified model, and the predicted concentrations of flame species agree reasonably well with the measured results. Early production of CO 2 was observed in the DMC-doped flame. Reaction flux analysis suggested that it was caused by the decomposition of CH 3OCO radical, DMC molecule and CH 3OCOO radical. As oxygenated fuels were added, the concentrations of most C 1C 5 hydrocarbon intermediates were reduced while that of benzene (C 6H 6) also decreased apparently, and the extent of benzene reduction showed little difference among the oxygenate-doped flames. Reaction flux analysis indicated that, in all the tested flames, the primary pathway leading from small aliphatics to C 6H 6 was through C 3+C 3 reactions, including the self-recombination reaction of propargyl radical (C 3H 3) and the cross reaction between C 3H 3 and allyl radical (a-C 3H 5). Considering that the temperatures of the tested flames were almost equivalent, the reduction of C 6H 6 concentration when doped with oxygenated fuels should be resulted from the reduced concentrations of its precursors. Furthermore, concentrations of certain oxygenated intermediates were also examined. The concentration of formaldehyde (CH 2O) was found to increase when flames were doped with oxygenated fuels, while those of acetaldehyde (CH 3CHO) and vinyl alcohol (C 2H 3OH) were nearly equivalent for all the flames. Methyl formate (CH 3OCHO) was detected only in the DMM-doped flame, which was attributed to the efficient CH 3OCHO formation pathway through the decomposition of CH 3OCHOCH 3 radical in the flame.

Original languageEnglish (US)
Pages (from-to)2324-2335
Number of pages12
JournalCombustion and Flame
Volume159
Issue number7
DOIs
StatePublished - Jul 1 2012

Keywords

  • Kinetic modeling
  • Molecular-beam sampling-mass spectrometry (MBMS)
  • N-Heptane premixed flame
  • Oxygenated additive
  • Tunable synchrotron photoionization

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Fuel Technology
  • Energy Engineering and Power Technology
  • Physics and Astronomy(all)

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