Lewis number effect on extinction characteristics of radiative counterflow CH4-O2-N2-He flames

Kaoru Maruta, Yiguang Ju, Atsutaka Honda, Takashi Niioka

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This work concentrates on general extinction characteristics of low-stretched premixed flames, that is, a change in extinction curve of radiative counterflow premixed flames with the Lewis numbers. To substantiate the occurrence of the change in extinction curves based on the Lewis numbers, flammable boundaries and flame bifurcation were studied by experiment and computation with detailed chemistry. Mixtures of methane and artificial air (O2-N2-He, the O2 mole fraction being fixed at 0.21, and those of N2 and He being varied) having four different Lewis numbers, that is, 0.97, 1.2, 1.4, and 1.8, were used. Experiments were carried out under microgravity of 10 s, and computation employing C1 chemistry was conducted taking radiative heat loss into account. The experimental results and those of detailed computation qualitatively agreed with each other and showed a change of extinction characteristics with the increase of Lewis numbers. We call this change "G-K transition," because the configuration of the extinction curve gradually changed from G-shaped to K-shaped with the increase of Lewis numbers. This transition clearly showed, the following: (1) the relation between counterflow flame and propagating plane flame, (2) the existence of a critical Lewis number where the lower limit of counterflow flame and the conventional 1-D limit coincide, and (3) the existence of a multiple solution region resulting from flame bifurcation. Furthermore, two pieces of supporting evidence for flame bifurcation were obtained by microgravity experiments. One is a discontinuous extinction curve due to separated extinction curves of the K-curve for Lewis number 1.8. The other is flame pulsation due to transient flame motion in the multiple solution region initiated by the diffusive-thermal instability of high Lewis number.

Original languageEnglish (US)
Pages (from-to)2611-2617
Number of pages7
JournalSymposium (International) on Combustion
Issue number2
StatePublished - 1998
Externally publishedYes
Event27th International Symposium on Combustion - Boulder, CO, United States
Duration: Aug 2 1998Aug 7 1998

All Science Journal Classification (ASJC) codes

  • General Chemical Engineering
  • Fuel Technology
  • Energy Engineering and Power Technology
  • Mechanical Engineering
  • Physical and Theoretical Chemistry
  • Fluid Flow and Transfer Processes


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