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http://dx.doi.org/10.3795/KSME-B.2012.36.2.181

Effect of Outer Edge Flame on Flame Extinction in Counterflow Diffusion Flames  

Chung, Yong-Ho (Dept. of Mechanical Engineering, Pukyoung Nat'l Univ.)
Park, Dae-Geun (Dept. of Mechanical Engineering, Pukyoung Nat'l Univ.)
Park, Jeong (Dept. of Mechanical Engineering, Pukyoung Nat'l Univ.)
Yun, Jin-Han (Environment & Energy Research Division, Korea Institute of Machinery and Materials)
Kwon, Oh-Boong (Dept. of Mechanical Engineering, Pukyoung Nat'l Univ.)
Keel, Sang-In (Environment & Energy Research Division, Korea Institute of Machinery and Materials)
Publication Information
Transactions of the Korean Society of Mechanical Engineers B / v.36, no.2, 2012 , pp. 181-188 More about this Journal
Abstract
The present study on nitrogen-diluted non-premixed counterflow flames with finite burner diameters experimentally investigates the important role of the outer edge flame in flame extinction. Flame stability diagrams mapping the flame extinction response of nitrogen-diluted non-premixed counterflow flames to varying global strain rates in terms of the burner diameter, burner gap, and velocity ratio are explored. There exists a critical nitrogen mole fraction beyond which the flame cannot be sustained, and also the curves of the critical nitrogen mole fraction versus the global strain rate have C-shapes in terms of burner diameter, burner gap, and velocity ratio. In flames with sufficiently high strain rates, the curves of the critical nitrogen mole fractions versus global strain rate collapse into one curve, and the flames can have the 1-D flame response of typical diffusion flames. Three flame extinction modes are identified: flame extinctions through the shrinkage of the outer edge flame with and without an oscillation of the outer edge flame prior to the extinction and flame extinction through a flame hole at the flame center. The measured flame surface temperature and a numerical evaluation of the fractional contribution of each term in the energy equation show that the radial conductive heat loss at the flame edge destabilizes the outer edge flame, and the conductive and convection heat addition to the outer edge from the trailing diffusion flame stabilizes the outer edge flame. The radial conductive heat loss at the flame edge is the dominant extinction mechanism acting through the shrinkage of the outer edge flame.
Keywords
Extinction; Flame Length; Heat Addition; Heat Loss; Oscillation; Outer Edge Flame;
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