• 한국연소학회:학술대회논문집
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• 1997.06a
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• pp.51-60
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• 1997

축대칭 곡면벽 제트 버너를 제작하여 화염의 안정화 특성을 실험적으로 연구하였다. 축대칭 곡면벽 제트 유동은 난류 강도의 증가와 더불어 버너 선단 부근에 재순환 영역을 형성하여 화염의 안정화를 촉진시킴으로서 기존의 튜브 버너에 비하여 화염의 안정화 특성이 향상되었다. 시간적으로 화염의 위치가 변동하는 난류 화염에서 화염의 안정화 특성과 밀접한 관계가 있는 OH 라디칼과 온도를 PLIF와 CARS를 각각 적용하여 측정하였다. 고유속으로 연소시키는 경우에 버너 선단에 형성된 재순환 영역에 OH 라디칼이 상당량 분포하고 있었으며 통계적으로 고온을 유지하였다. 이는 버너 선단에 형성되는 재순환 영역에 고온의 기연 가스가 점화원 역할을 하여 화학 반응이 활발하게 일어나고 있음을 의미한다. 이러한 결과로부터 고속의 출구유속에서 화염 안정화 특성은 재순환 영역에 의하여 영향을 받고 있음을 확인하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.4
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• pp.104-111
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• 2016

The flame stabilization is one of the topics which have to be solved for the airbreathing propulsion systems, using the entering air which is supersonic velocity as an oxygen sources. Making a recirculation zone with an eddy flow, installed the reducing velocity devices such as the bluff body, is the typical method of the flame stabilization. Recently using a cavity flame stabilization at the wall is an emerging technique as an effective method which extends the stabilization zone, and the related research papers have been published on the flow separation and reattachment, pressures and oscillations including length/depth ratios in the cavities. Even though, still there are lots of topics to study more in the cavity flame stabilization field as the preceding techniques, as well as the research and the development of the airbreathing propulsion system itself.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.4
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• pp.26-34
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• 2011

The present work addresses structural characteristics of natural gas flames in a lean premixed swirl-stabilized combustor with an attention focused on the effect of the formation of recirculation zones on the combustion instability. It is known that the recirculation zone plays an important role in stabilizing a turbulent, premixed natural gas flames by providing a source of heat or radicals to the incoming premixed fuel and air. To improve our understanding of the role of recirculation zones, the flame structure was investigated for various mixture velocities, equivalence ratios and swirl numbers. The optically accessible combustor allowed for the application of laser diagnostics, and Particle Image Velocimetry(PIV) measurements was used to characterize the flame structure under both cold flow conditions and hot flow conditions. Dynamic pressures were also measured to investigate characteristics of combustion at the same time. The results indicates that the formation of recirculation zone is strongly related to the occurrence of thermo-acoustic instabilities.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.04a
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• pp.25-25
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• 1999

안정화 화염으로 수소 확산 화염을 이용한 메탄/공기 난류 예혼합 화염의 미연가스 영역의 난류 특성을 측정하였다. 측정은 동일한 위치에 대해서 화염이 존재할 때와 존재하지 않을 때에 대해 수행되었다. 버너 출구 레이놀즈 수 7000에서 당량비 0.6과 1.0의 경우에 대해 실험이 수행되었다. 난류 유동장은 2색 레이저 유속계에 의해 측정되었다. 21개의 위치에 대해서 반복적으로 측정이 수행되었다.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.4
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• pp.33-42
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• 2014

Flame behaviors and interaction between pilot and main flames in a dual swirl combustor were investigated experimentally and numerically. Under the condition of fixed swirl angle of $45^{\circ}$ for main flame, the swirl angle of pilot flame, total heat release rate and equivalence ratio of main flame were used as major parameters. As a result, detailed flame stability diagram of dual swirl combustor was identified in terms of 5 flame modes with the changes in total heat release rate and equivalence ratio of main flame. It was found that the swirl angle of pilot flame plays the most important role in the changes in flame location and overall flow structure inside the combustor, and thus leads to the significant change in the interaction between pilot and main flame.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.445-452
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• 2011

The present work addresses structural characteristics of natural gas flames in a lean premixed swirl-stabilized combustor with an attention focused on the effect of the formation of recirculation zones on the combustion instability. It is known that the recirculation zone plays an important role in stabilizing a turbulent, premixed natural gas flames by providing a source of heat or radicals to the incoming premixed fuel and air. To improve our understanding of the role of recirculation zones, the flame structure was investigated for various mixture velocities, equivalence ratios and swirl numbers. The optically accessible combustor allowed for the application of laser diagnostics, and Particle Image Velocimetry(PIV) measurements was used to characterize the flame structure under both cold flow conditions and hot flow conditions. Dynamic pressures were also measured to investigate characteristics of combustion at the same time. The results indicates that the formation of recirculation zone is strongly related to the occurrence of thermo-acoustic instabilities.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.395-396
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• 2014

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.4
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• pp.497-508
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• 1985

본 논문에서는 일양한 예혼합 기류중에 놓여진 원주 후류의 고온 순환류에 의 해 보지되는 난류 예혼합 화염을 대상으로 해서 유동의 가시화 및 온도와 이온전류의 변동의 측정에 의해서 화염의 구조를 조사한 결과, 원주 보염기 후류의 재순환 영역부 근에 형성된 전단층에 있어서는 코히렌트(Coherent)구조의 화염이 되고 하류부에서는 불규칙한 3차원 와(渦)에 지배되는 전파성 화염이 형성 되었다. 온도변동에 대한 쌍 봉성의 확율밀도분포와 이온전류변동에 대한 3개의 피이크의 확율밀도분포는 엷은 반 응면을 사이에 두고 미연혼합기괴와 기연가스괴가 서로 접하는 주름 상층류화염 또는 층류화염편의 구조에 대응하며, 코히렌트 와(渦)에 지배되는 화염에 있어서는 거시적 혼합은 코히렌트 와의 거동에 지배되나 그 구조는 주름상층류 화염과 일부 강한 전단 력을 받는 부분에는 분산 반응영역의 구조임이 밝혀졌다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.6
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• pp.639-646
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• 2012

The characteristics of autoignited lifted flames in laminar jets of carbon monoxide/hydrogen fuels have been investigated experimentally in heated coflow air. In result, as the jet velocity increased, the blowoff was directly occurred from the nozzle-attached flame without experiencing a stabilized lifted flame, in the non-autoignited regime. In the autoignited regime, the autoignited lifted flame of carbon monoxide diluted by nitrogen was affected by the water vapor content in the compressed air oxidizer, as evidenced by the variation of the ignition delay time estimated by numerical calculation. In particular, in the autoignition regime at low temperatures with added hydrogen, the liftoff height of the autoignited lifted flames decreased and then increased as the jet velocity increased. Based on the mechanism in which the autoignited laminar lifted flame is stabilized by ignition delay time, the liftoff height can be influenced not only by the heat loss, but also by the preferential diffusion between momentum and mass diffusion in fuel jets during the autoignition process.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.7
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• pp.729-738
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• 2010

The characteristics of lifted butane flames diluted with nitrogen have been investigated experimentally in order to elucidate the mechanism of individual flame oscillation modes. Flame oscillations in laminar free-jet lift-off flames are classified into the following five regimes: a stabilized lift-off regime (I), a heat-loss-induced oscillation (II), a buoyancy-induced oscillation along with a heat-loss-induced oscillation (III), a combined form of an oscillation prior to blow-out and a heat-loss-induced oscillation (IV), and a combination of an oscillation prior to blow-out and a buoyancy-induced oscillation along with a heat-loss-induced oscillation (V). The characterization of the individual flame oscillations modes are presented and discussed using Strouhal numbers and their relevant parameters by the analysis of the power spectrum for temporal variation of the lift-off height.