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Experimental Study of Transition to Secondary Acoustic Instability at Downward-Propagating Premixed Flame in a Tube

튜브 내 하향 전파하는 예혼합 화염의 이차 열음향 불안정성 천이에 관한 실험적 연구

  • Park, Juwon (Division of Marine System Engineering, Korea Maritime & Ocean University) ;
  • Kim, Daehae (Clean Energy System R&D Department, Korea Institute of Industrial Technology (KITECH)) ;
  • Park, Dae Geun (Clean Energy System R&D Department, Korea Institute of Industrial Technology (KITECH)) ;
  • Yoon, Sung Hwan (Division of Marine System Engineering, Korea Maritime & Ocean University)
  • 박주원 (한국해양대학교 기관시스템공학부) ;
  • 김대해 (한국생산기술연구원 청정에너지시스템연구부문) ;
  • 박대근 (한국생산기술연구원 청정에너지시스템연구부문) ;
  • 윤성환 (한국해양대학교 기관시스템공학부)
  • Received : 2020.11.02
  • Accepted : 2020.12.28
  • Published : 2020.12.31

Abstract

Thermoacoustic instability caused by air conditioning in a combustion chamber has emerged as a problem that must be solved to establish a stable combustion system. Thermoacoustic instability is largely divided into primary and secondary acoustic instability. In this study, an experimental study of the effects of heat losses was conducted to investigate the mechanism of secondary acoustic instability. To generate the secondary acoustic instability, a quarter-wavelength resonator with one open end and one closed end was used, and the inside of the resonator was filled with premixed gases. Subsequently, secondary acoustic instability with downward-propagating flames could be realized via thermal expansion on the burnt side. To control heat losses qualitatively, an additional co-axial tube was installed in the resonator with air or nitrogen supply. Therefore, additional diffusion flames can be formed at the top of the resonator depending on the injection of the oxidizer into the co-axial tube when rich premixed flames are used. Consequently, secondary acoustic instability could not be achieved by increasing heat losses to the ambient when the additional diffusion flame was not formed, and the opposite result was obtained with the additional diffusion flame.

연소실 내 공조현상으로 인해 발생되는 열음향 불안정성은 안정적인 연소시스템을 구현하기 위해 해결해야 하는 고질적인 문제로 제기되어 왔다. 열음향 불안정성은 크게 1차 2차 열음향 불안정성으로 나뉘며, 본 연구에서는 열음향 불안정성 중 2차 열음향 불안정성의 천이에 관해 열손실이 미치는 영향에 대한 실험적 연구를 진행하였다. 2차 열음향 불안정성을 발생시키기 위해 한쪽 끝이 열린 1/4 파장 공명기를 채택하여 수직으로 설치하였고, 공명기 내부에는 예혼합 가스를 주입하였다. 또한 공명기 상단으로 발생하는 열손실 효과를 비교하기 위해 추가적으로 외부 동축류 관을 설치하였다. 연료 농후조건의 예혼합 가스만을 채택하여 주입하였기 때문에 동축관에 주입되는 기체에 따라 공명기 상부에 추가적인 확산화염이 형성될 수 있다. 그 결과 확산화염이 발생되었을 경우 공명기 상단으로의 열손실이 감소하며 2차 열음향 불안정성이 발현되었으며, 확산화염이 억제되어 공명기 상단으로의 열손실이 증가하였을 경우 2차 열음향 불안정성의 발현이 억제되는 결과를 도출하였다.

Keywords

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