Transactions of the Korean Society of Mechanical Engineers B (대한기계학회논문집B)

The Korean Society of Mechanical Engineers (대한기계학회)
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Effect of Outer Edge Flame on Flame Extinction in Counterflow Diffusion Flames

대향류 확산화염에서 에지화염이 화염소화에 미치는 영향

  • 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)
  • 정용호 (부경대학교 기계공학과) ;
  • 박대근 (부경대학교 기계공학과) ;
  • 박정 (부경대학교 기계공학과) ;
  • 윤진한 (한국 기계연구원 그린환경에너지기계본부) ;
  • 권오붕 (부경대학교 기계공학과) ;
  • 길상인 (한국 기계연구원 그린환경에너지기계본부)
  • Received : 2011.08.09
  • Accepted : 2011.10.20
  • Published : 2012.02.01
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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.

대향류확산화염의 화염소화에 있어서 에지화염 역할에 관한 실험적 연구가 진행되었다. 속도비, 버너직경, 그리고 버너간격을 변화시키며 수행된 실험에서 전체신장률에 따른 화염소화 임계질소몰분율의 그래프는 c-커브 형태로 나타났다. 고신장률화염에서는 화염소화 임계질소몰분율의 그래프가 하나의 곡선으로 일치하였으며, 화염이 일차원의 응답특성을 갖는 것을 확인하였다. 화염 소화는 바깥 에지화염이 반경방향으로의 진동 후에 화염 중심으로 수축하며 소화하는 영역, 진동 없이 화염중심으로 수축하며 소화하는 영역, 그리고 바깥 에지부분의 수축과 진동 없이 화염중심에 화염 구멍이 생기며 소화하는 영역으로 세 가지 모드로 나타났다. 화염 표면온도 측정과 에너지 방정식의 각항을 수치해석 한 결과를 토대로 에지화염부분에서의 반경방향 전도 열손실이 에지화염의 불안정을 야기한다는 것과 전도를 통한 열 공급뿐만 아니라 대류를 통한 열 공급도 바깥 에지화염의 안정화에 기여한다는 것을 보였다. 그리고 반경방향의 전도열손실이 수축하며 소화하는 메커니즘의 지배적인 역할을 함을 보였다.

Keywords

References

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