Propagation rates of nonpremixed edge flames

Min Suk Cha*, Paul D. Ronney

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

81 Scopus citations

Abstract

The propagation rates (Uedge) of nonpremixed ignition (advancing) fronts and extinction (retreating) edge flames were measured as a function of global strain rate (σ), jet spacing (d), mixture strength, stoichiometric mixture fraction (Zst), and Lewis number (Le) using a counterflow slot-jet burner in which edge flames propagated along its long dimension. Electrical heaters at both ends of the slot "anchored" the flames, allowing conditions resulting in negative values of Uedge to be studied by triggering local extinction of anchored flames with an N2 jet. Results are presented in terms of the effects of a dimensionless flame thickness (ε) related to σ and a dimensionless heat loss (κ) on a scaled Uedge. Propagation rates were markedly enhanced/retarded in mixtures with low/high Le. Propagation rates and extinction conditions were highly asymmetric with respect to Zst = 0.5 despite the symmetry of flame location; mixtures with Zst greater/less than 0.5 behaved like stronger/weaker mixtures, apparently due to the relative locations of the radical production zone and maximum temperature zone for varying Zst. Two extinction limits were identified, corresponding to a high-σ strain-induced limit that was strongly dependent on Le but nearly independent of κ and a low-σ heat-loss-induced limit that was strongly dependent on κ but not Le. Most experimental findings were in good agreement with theoretical predictions; however, unlike predictions, "tailless" triple flames were not observed; instead standard triple flames and "short length" edge flames were found, and only for a very narrow range of experimental conditions. This is proposed to be due to the difference between the volumetric heat loss presumed in the models and the conductive transfer to the jet exits that dominates heat loss in the experiments.

Original languageEnglish (US)
Pages (from-to)312-328
Number of pages17
JournalCombustion and Flame
Volume146
Issue number1-2
DOIs
StatePublished - Jul 1 2006

Keywords

  • Advancing edge
  • Nonpremixed edge flame
  • Retreating edge
  • Short-length flame
  • Triple flame

ASJC Scopus subject areas

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

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