• Title/Summary/Keyword: 대향류 확산화염

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Instability Analysis of Counterflow Diffusion Flames with Radiation Heat Loss (복사 열손실을 받는 대향류 확산화염의 불안정성 해석)

  • Lee, Su-Ryong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.36 no.8
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    • pp.857-864
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    • 2012
  • A linear stability analysis of a diffusion flame with radiation heat loss is performed to identify linearly unstable conditions for the Damk$\ddot{o}$hler number and radiation intensity. We adopt a counterflow diffusion flame with unity Lewis number as a model. Near the kinetic limit extinction regime, the growth rates of disturbances always have real eigenvalues, and a neutral stability condition perfectly falls into the quasi-steady extinction. However, near the radiative limit extinction regime, the eigenvalues are complex, which implies pulsating instability. A stable limit cycle occurs when the temperatures of the pulsating flame exceed the maximum temperature of the steady-state flame with real positive eigenvalues. If the instantaneous temperature of the pulsating flame is below the maximum temperature, the flame cannot recover and goes to extinction. The neutral stability curve of the radiation-induced instability is plotted over a broad range of radiation intensities.

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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    • 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.

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Structure and Suppression of Nonpremixed Counterflow Flames (비예혼합 대향류화염의 구조와 소화)

  • Anthony Hamins;Park, Woe-Chul
    • Fire Science and Engineering
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    • v.17 no.3
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    • pp.20-25
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    • 2003
  • Measurements with filaments and thermocouples and computations with Oppdif and FDS were carried out to investigate the impact of flame strain, agent addition, and buoyancy on the structure and extinction of nonpremixed counterflow flames. Measurements through 2.2 s drop tests in microgravity conditions and experiments in normal gravity conditions were compared with the results of computations. For the global strain rates 7 s$^{-1}$ through 100 s$^{-1}$ , the turning point behavior in the critical nitrogen concentration at O-g was confirmed. The effects of buoyancy, that is, changes in the flame curvature and thickness were also confirmed by the computations with FDS. There was agreement in the peak flame temperature and its position between the computations and the measurements in the near extinction methane/air diffusion flames in microgravity.

Effect of $CO_2$ Addition on Flame Structure and NOx Formation of $CH_4-Air$ Counterflow Diffusion Flames ($CO_2$ 첨가가 $CH_4$-공기 대향류 확산화염의 구조 및 NOx 생성에 미치는 영향)

  • Lee, S.R.;Han, J.W.;Lee, C.E.
    • Journal of the Korean Society of Combustion
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    • v.4 no.2
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    • pp.97-108
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    • 1999
  • This numerical study was to investigate the effect of $CO_2$ addition on the structures and NOx formation characteristics in $CH_4$ counterflow diffusion flame. The importance of radiation effect was identified and $CO_2$ addition effect was investigated in terms of thermal and chemical reaction effect. Also the causes of NOx reduction were clarified by separation method of each formation mechanisms. The results were as follows : The radiation effect was intensified by $CO_2$ addition. Thermal effect mainly contributed to the changes in flame structure and the amount of NO formation but the chemical reaction effect also cannot be neglected. The reduction of thermal NO was dominant with respect to reduction rate, but that of prompt NO was dominant with respect to total amount.

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Numerical Study on Soot Formation in Opposed-flow Nonpremixed Flame by Mixing Toluene (톨루엔 혼합에 따른 대향류 확산화염 내 매연 생성에 대한 수치적 연구)

  • Choi, Jae-Hyuk;Yoon, Seok-Hun;Yoon, Doo-Ho
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.18 no.2
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    • pp.139-144
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    • 2012
  • A numerical simulation has been performed to investigate effects of toluene mixing on soot formation in pure ethylene opposed-flow nonpremixed flame. Mixture ratios of toluene were 3%, 5%, 10%, and 20%. Senkin code for 0-D simulation and oppdif code for 1-D simulation based on CHEMKIN III were utilized. 0-D results by senkin showed that concentrations of methyl radicals and benzene were increased with increasing toluene mixture ratio. This implied that the mixing of toluene in pure ethylene diffusion flame produces more PAHs and soot than those of pure ethylene flame. 1-D result of 10 % toluene reaction by oppdif code showed that production rate for H radical was a crucial factor for benzene formation. These results imply that methyl radical, benzene and H radical play a important role on soot formation in diffusion flames.

Experimental Study on Soot Formation in Opposed-Flow Ethylene Diffusion Flames by Mixing DME as an Alternative Fuel (대체 연료인 DME 혼합에 의한 대향류 에틸렌 확산화염내 매연 생성에 대한 실험적 연구)

  • Yoon, Doo-Ho;Yoon, Seok-Hun;Choi, Jae-Hyuk
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.16 no.3
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    • pp.301-306
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    • 2010
  • DME(Di-Methyl Ehter, $CH_3OCH$) is currently attracting worldwide attention due to its environmentally friendly characteristics. Until now it was researched as a major alternative fuel of diesel automobile because it is a clean fuel producing low soot. Therefore, in this study, in order to investigate the effect of DME mixing on number density and size of soot particle, DME has been mixed in opposed-flow ethylene diffusion flame with the mixture ratios 5%, 14% and 30%. A laser extinction/scattering technique has been adopted to measure the volume fraction, number density, and size of soot particles. The experimental results showed that the soot concentration of mixture flames with the mixture ratios 5% and 14% produces soot more, even though that of 30% was decreased. This means that even though DME has been known to be a clean fuel for soot formation, the mixing of DME in diffusion flame of ethylene, where acetylene maintains high concentration in soot formation regions, could produce enhanced production of soot.

A Study on Transition of Flame Extinction at Low Strain Rate Counterflow Flames (저신장율 대향류화염에서 화염소화에 있어서 천이에 대한 연구)

  • Park, Dae-Geun;Park, Jeong;Kim, Jeong-Soo;Bae, Dae-Suk
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2009.11a
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    • pp.197-201
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    • 2009
  • Experiments were conducted to study the transition of shrinking flame disk to flame hole in counterflow diffusion flames. The studies of transition are well described by varying burner diameters, global strain rate and velocity ratio. It is experimentally verified that radial conduction heat loss is affected at even high strain rate flames for appropriately small burner diameters. It is also shown that flame extinction modes are grouped into three and particularly, hole or stripe is observed in sufficiently high strain rate flames. There exists critical radius according to burner diameter which divide flame extinction modes into three parts.

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A Study on Flame Extinction and Edge Flame Oscillation in Counterflow Diffusion Flame (대향류확산화염에서 화염소화와 에지화염진동에 관한 연구)

  • Park, Dae-Geun;Yun, Jin-Han;Park, Jeong;Keel, Sang-In
    • 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.