• 한국연소학회:학술대회논문집
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• 2006.10a
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.9 s.252
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.10 s.253
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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

• 한국연소학회:학술대회논문집
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• 2007.05a
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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.

• 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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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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.

• Journal of the Korean Society of Combustion
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• v.13 no.4
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• pp.26-36
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• 2008

Experimental study is conducted to identify the existence of a shrinking flame disk and to clarify its flame characteristics through the inspection of critical mole fraction at flame extinction and edge flame oscillation at low strain rate flames. Experiments are made as varying global strain rate, velocity ratio, and burner distance. The transition from a shrinking flame disk to a flame hole is verified through gradient measurements of maximum flame temperature. The evidence of edge flame oscillation in flame disk is also provided through numerical simulation in microgravity. It is found at low strain rate flame disks in normal gravity that buoyancy effects are importantly contributing to lateral heat loss to burner rim, and is proven through critical mole fraction at flame extinction, edge flame oscillation, and measurements of flame temperature gradient along flame disk surface.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.81-84
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• 2014

A Experimental study on flame extinction behavior was investigated using He curtain flow with counter triple co-flow burner. Buoyancy force was suppressed up to a microgravity level of $10^{-2}-10^{-3}g$ by using He curtain flow. The stability maps were provided with a functional dependency of diluent mole fraction and global strain rate to clarify the differences in flame extinction behavior. The flame extinction curves had C-shapes at various global strain rates. The oscillation and extinction modes were different each other in terms of the global strain rate, and the flames extinction modes could be classified into five modes such as (I) and (II): an extinction through the shrinkage of the outmost edge flame forward the flame center after self-excitation and without self-excitation, respectively, (III): an extinction through rapid advancement of a flame hole while the outmost edge flame is stationary, (IV): self-excitation occurs in the outermost edge flame and the center edge flame and then a donut shaped flame is formed and/or the flame is entirely extinguished, (V): shrinkage of the outermost edge flame without self-excitation followed by shrinkage or survival of the center flame. These oscillation and extinction modes could be identified well to the behavior of edge flame. The result also showed that the edge flame was influenced significantly by the conductive heat losses to the flame center or ambient He curtain flow.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.2
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• pp.64-76
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• 2009

Experimental and numerical studies are conducted on the characteristics of flame extinction and edge flame oscillation in counterflow diffusion flames. The characteristics of flame extinction and edge flame oscillation are well described varying burner diameter, separation distance between two burners, global strain rate, and velocity ratio. It is verified numerically and experimentally that radial conduction heat loss significantly contributes to flame extinction and edge flame oscillation at low strain rate flames in zero- and micro-gravity. It is also shown that for appropriately small burner diameters flame extinction modes are grouped into four and these are significantly attributed to excessive radial conduction heat loss. The edge flame oscillation can be characterized well by one curve with Strouhal number and Peclet number.