• Title, Summary, Keyword: Flame oscillation

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Dynamic Behaviors of Oscillating Edge-Flame in Low Strain Rate Counterflow Diffusion Flames (저신장율 대향류확산화염에서 진동불안정성을 갖는 에지화염의 동적거동)

  • Park, June-Sung;Kim, Hyun-Pyo;Park, Jeong;Kim, Jeong-Soo;Keel, Sang-In
    • 한국연소학회:학술대회논문집
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    • pp.65-72
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    • 2006
  • Experiments in methane-air low strain rate counterflow diffusion flames diluted with nitrogen have been conducted to study the behavior of flame extinction and edge flame oscillation in which flame length is less than the burner diameter and thus lateral conduction heat loss in addition to radiative heat loss could be remarkable at low global strain rates. Critical mole fraction at flame extinction is examined with velocity ratio and global strain rate. Onset conditions of edge flame oscillation and flame oscillation modes are also provided with global strain rate and added nitrogen mole fraction to fuel stream (fuel Lewis number). It is seen that flame length is closely relevant to lateral heat loss, and this affects flame extinction and edge flame oscillation considerably. Edge flame oscillations in low strain rate flames are experimentally described well and are categorized into three: a growing oscillation mode, a decaying oscillation mode, and a harmonic oscillation mode. The regime of flame oscillation is also provided at low strain rate flames. Important contribution of lateral heat loss even to edge flame oscillation is clarified.

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An experimental study on instability and control of co-flow diffusion flames (동축류 확산화염의 불안정성과 제어에 관한 실험적 연구)

  • Lee, Hyeon-Ho;Hwang, Jun-Yeong;Jeong, Seok-Ho;Lee, Won-Nam
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.1
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    • pp.153-164
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    • 1997
  • Flame oscillation phenomena in a co-flow diffusion flame was experimentally studied with periodic fuel supply using a solenoid valve. The degree of excitation was controlled by changing the volume flux of fuel passing through the valve. Flame oscillation frequencies were measured utilizing a photodiode, a spectrum analyzer, video and high speed movies. Laser planar visualization was employed to study the correlation between the flame oscillation and the toroidal vortices. Observed are three regimes of flame oscillation, where the oscillation frequencies are for the multiples of excitation, the excitation itself and the flame natural oscillation. Both periods of natural oscillation and of excitation induced oscillation exist over one cycle of the excitation in the frequency multiplied regime. It is considered as an effect of balancing the influence of buoyancy driven vortex with that of excitation induced vortex near the excitation rate of 0.2. Flame shapes are become monotonous as increasing the excitation frequency to the range of over two fold of the natural oscillation. The flame oscillation can be modulated to the frequency of either multiples of excitation or excitation itself under certain conditions. This implies that the flame oscillation could be modulated to avoid the resonance frequency of the combustor, and shows the possibility of active control of the flame oscillation.

Edge Flame Instability of CH4-Air Diffusion Flame Diluted with CO2 (이산화탄소로 희석된 메탄-공기 확산화염의 에지화염 불안정성)

  • Hwang, Dong-Jin;Kim, Jeong-Soo;Keel, Sang-In;Kim, Tae-Kwon;Park, Jeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.9
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    • pp.905-912
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    • 2006
  • Experiments in low strain rate methane-air counterflow diffusion flames diluted with $CO_2$ have been conducted to investigate the flame extinction behavior and edge flame oscillation in which flame length is less than the burner diameter and thus lateral conductive heat loss in addition to radiative loss could be remarkable at low global strain rates. The critical mole fraction at flame extinction is examined in terms of velocity ratio and global strain rate. It is seen that flame length is closely relevant to lateral heat loss, and this sheets flame extinction and edge flame oscillation considerably. Lateral heat loss causes flame oscillation even at fuel Lewis number less than unity. Edge flame oscillations are categorized into three: a growing-, a harmonic- and a decaying-oscillation mode. Onset conditions of the edge flame oscillation and the relevant modes are examined with global strain rate and $CO_2$ mole fraction in fuel stream. A flame stability map based on the flame oscillation modes is also provided at low strain rate flames.

Effects of Heat Losses on Edge-flame Instabilities in Low Strain Rate Counterflow Diffusion Flames (저신장율 대향류확산화염에서 에지화염 불안정성에 관한 열손실 효과)

  • Park June-Sung;Hwang Dong-Jin;Kim Jeong-Soo;Keel Sang-In;Kim Tae-Kwon;Park Jeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.10
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    • pp.996-1002
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    • 2006
  • Experiments in methane-air low strain rate counterflow diffusion flames diluted with nitrogen have been conducted to study the behavior of flame extinction and edge flame oscillation in which flame length is less than the burner diameter and thus lateral conduction heat loss in addition to radiative heat loss could be remarkable at low global strain rates. Critical mole fraction at flame extinction is examined with velocity ratio and global strain rate. Onset conditions of edge flame oscillation and flame oscillation modes are also provided with global strain rate and added nitrogen mole fraction to fuel stream (fuel Lewis number). It is seen that flame length is closely relevant to lateral heat loss, and this affects flame extinction and edge flame oscillation considerably. Edge flame oscillations in low strain rate flames are experimentally described well and are categorized into three: a growing oscillation mode, a decaying oscillation mode, and a harmonic oscillation mode. The regime of flame oscillation is also provided at low strain rate flames. Important contribution of lateral heat loss even to edge flame oscillation is clarified

Observation of flame oscillation with changing combustor pressure (연소실 압력변동에 따른 화염 진동현상의 관찰)

  • Kim, Jong-Ryul;Choi, Gyung-Min;Kim, Duck-Jool
    • 한국연소학회:학술대회논문집
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    • pp.275-280
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    • 2005
  • At previous study, nitrogen oxide emission was decreased with decreasing pressure index. This tendency was explained by the flame oscillation with changing combustor pressure. In this study, the characteristics of flame oscillation with changing combustor pressure were investigated. It can be found that flame length is extended and flame width is narrowed by decreasing combustor pressure. It can be observed that pilot flame and the surrounding air converge on the inner flame in the $P^{\ast}{\geqq}1$ conditions and that surrounding air and flow pattern was widely dispersed in the $P^{\ast}<1$ conditions. In the respect of average flame length, low fluctuation was shown in the $P^{\ast}<1$ conditions. On the other hands, large fluctuation was shown in the $P^{\ast}<1$ conditions. Flame oscillation are observed from $P^{\ast}=$ 0.98 in the condition of $P^{\ast}<1$ and the amplitude of flame oscillation becomes larger when $P^{\ast}$ is lowered. These results demonstrate that low NOx phenomenon was caused by flame oscillation with changing combustor pressure.

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Edge-flame Instability in A Low Strain-rate Counterflow Diffusion Flame (저신장율 대향류확산화염에서 에지화염 진동불안정성)

  • Park, June-Sung;Kim, Hyun-Pyo;Park, Jeong;Kim, Song-Cho;Kim, Jeong-Soo
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.295-298
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    • 2006
  • Experiments in methane-air low strain rate counterflow diffusion flames diluted with nitrogen have been conducted to study the behavior of flame extinction and edge flame oscillation in which lateral conduction heat loss in addition to radiative heat loss could be remarkable at low global strain rates. Onset conditions of edge flame oscillation and flame oscillation modes are also provided with global strain rate. It is seen that flame length is closely relevant to lateral heat loss, and this affects flame extinction and edge flame oscillation. Edge flame oscillations in low strain rate flames are categorized into three: a growing oscillation mode, a decaying oscillation mode, and a harmonic oscillation mode. The regime of flame oscillation is also provided at low strain rate flames.

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Acceleration in Diffusive-thermal Instability by Heat Losses (열손실에 의한 확산-열 불안정성의 가속화)

  • Park, June-Sung;Park, Jeong;Lee, Kee-Man;Kim, Jeong-Soo;Kim, Sung-Cho
    • 한국연소학회:학술대회논문집
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    • pp.145-152
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    • 2007
  • The dynamic behaviors of counterflow non-premixed flame have been investigated experimentally to study effects of heat losses on edge flame oscillation, which result from the advancing and retreating edge flame motion of outer flame edge at low strain rate flame. For low strain rate flame, lateral conduction heat loss in addition to radiation heat loss could be more remarkable than the others. Oscillatory instabilities appear at fuel Lewis number greater than unity. But excessive lateral conduction heat loss causes edge flame instability even at fuel Lewis number less than unity. The dramatic change of burner diameters in which flame length is an indicator of lateral conduction heat loss was applied to examine the onset condition of edge flame oscillation and flame oscillation modes. Especially, extinction behaviors quite different from the previous study were observed.

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A Study on Effects of Flame Curvature in Oscillatory Laminar Lifted-flames (진동하는 층류부상화염에서 화염곡률 효과에 관한 연구)

  • Yoon, Sung-Hwan;Park, Jeong;Kwon, Oh-Boong;Yun, Jin-Han;Keel, Sang-In
    • Journal of the Korean Society of Combustion
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    • v.14 no.1
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    • pp.1-8
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    • 2009
  • Experiment is conducted to grasp effects of flame curvature on flame behavior in laminar lifted-jet flames. Nozzle diameters of 0.1 and 1.0mm are used to vary flame curvature of edge flame. There exist three types of edge flame oscillation. These edge flame oscillations may be caused by radial heat loss at all flame conditions, by fuel Lewis numbers near or larger than unity with the help of appreciable radial conduction heat loss, and by buoyancy effects. These are confirmed by the analysis of oscillation frequencies. It is however seen that the change of lift-off height through edge-flame oscillation is mainly due to radial heat loss irrespective of Lewis number and buoyancy.

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A study of Instability on Oscillating Laminar Premixed Flames (진동하는 층류예혼합화염의 불안정성에 관한 연구)

  • Lee, Won-Nam
    • Journal of the Korean Society of Combustion
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    • v.13 no.4
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    • pp.8-15
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    • 2008
  • When a circular cylinder is placed at the center of a slot burner nozzle, once stable Woflhard-Parker type laminar lean premixed flame is changed to an oscillating flame with self-induced noise. The wrinkled flame surface showed the same pattern and frequency of the Karman vortex street at the downstream of a circular cylinder. The interaction of flame with Karman vortex street is observed to be responsible for flame oscillation. The measured flame oscillation frequency is very similar to the estimated Karman vortex shedding frequency based on the St-Re relationship of the flow past circular cylinder, which could be considered as a strong evidence for the interaction between laminar pre-mixed flame and a Karman vortex street. As Reynolds number increases oscillation frequency decreases and the self-induced noise level increases as well as the flame front is more severly wrinkled. This result suggests that the flame/vortex interaction becomes more active at higher Re.

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Experimental Study on Edge Flame Instabilities in Solid Rocket Combustion (고체로켓연소에서 에지화염 불안정성에 대한 실험적 연구)

  • Hwang Dong-Jin;Park Jeong;Kim Jeong-Soo;Kim Sung-Cho;Kim Tae-Kwon
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.279-282
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    • 2006
  • Experiments in low strain rate methane-air counterflow diffusion flames diluted with $CO_2$ have been conducted to investigate the flame extinction behavior and edge flame oscillation The critical mole fraction at flame extinction is examined in terms of velocity ratio and global strain rate. Onset conditions of the edge flame oscillation and the relevant modes are also provided with global strain rate. It is observed that flame length is intimately relevant to lateral heat loss, and this affects flame extinction and edge flame oscillation considerably. Edge flame oscillations are categorized into three: a growing-, a decaying-, and a harmonic-oscillation mode.

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