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

The Korean Society of Mechanical Engineers (대한기계학회)
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The Effects of Velocity and Concentration in the Oxidizer of Heptane Pool Fires on the Flame Stability

헵탄 풀화재 화염안정성에 관한 산화제 유속 및 농도 효과

  • Jeong, Tae-Hee (Dept. of Safety Engineering, Pukyoung Nat'l Univ.) ;
  • Lee, Eui-Ju (Dept. of Safety Engineering, Pukyoung Nat'l Univ.)
  • 정태희 (부경대학교 안전공학과) ;
  • 이의주 (부경대학교 안전공학과)
  • Received : 2011.10.11
  • Accepted : 2011.12.02
  • Published : 2012.03.01
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Abstract

Flame flickering occurs mainly because of the buoyancy force for pool fires under ambient air. The cup-burner flame was used for experimental investigation of the effect of the oxidizer velocity on the gravitational instability. The results showed that the flickering frequency decreased with increasing oxidizer velocity. The frequency-buoyancy relation with nondimensional variables coincided with that of the buoyant flume and pool fires when the characteristic velocity was defined as the difference between the fuel and oxidizer velocities, which implies that the origin of the gravitational instability is the Kelvin-Helmholtz instability in the shear layer. The effect of the oxidizer composition on the instability was also examined through nitrogen dilution in the oxidizer stream. As the concentration of inert gas increased, the length of the blue flame increased and lift-off behavior was observed. The oscillation frequency was independent of the dilution ratio, but was related to the local flame structure.

풀화재에서 화염진동은 주위공기와의 밀도차에 의한 부력효과에 기인하여 주로 발생한다. 본 연구에서는 부력이 지배적인 풀화재의 불안전성에 대하여 산화제유속의 효과를 검토하기 위해 컵버너 실험을 수행하였다. 실험결과는 진동주파수가 산화제의 유속이 증가함에 따라 감소함을 보인다. 무차원 변수로 표현되는 주파수와 부력의 관계로 도시하였을 때 다양한 속도스케일을 사용할 수 있었지만, 연료와 산화제의 유속차로 정의되는 특성속도인 경우에 정지되어 있는 공기중에서의 풀화재 진동과 일치하는 관계식을 얻을 수 있었다. 이러한 사실은 부력이 지배적인 화염에서 불안전성의 원인은 전단면에서의 Kelvin-Helmholtz 불안전성이 주된 기구라는 것을 증명해준다. 산화제의 농도를 변화시켰을 경우에는 산화제의 불활성기체의 농도가 증가할수록 청염의 길이가 길어지고 컵버너 끝단으로부터 부상되는 것이 관찰된다. 또한 진동주파수는 희석율과는 특정한 관계를 보이지 않는데 이는 국부적 화염구조와 연관성을 가지기 때문으로 판단된다.

Keywords

References

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  1. Flame Instability in Heptane Pool Fires Near Extinction vol.36, pp.12, 2012, https://doi.org/10.3795/KSME-B.2012.36.12.1193