• Title/Summary/Keyword: Lifted flame

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A Transitional Behavior of a Premixed Flame and a Triple Flame in a Lifted Flame(II) (부상화염에서 예혼합화염과 삼지화염의 천이적 거동(II))

  • Jang Jun Young;Kim Tae Kwon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.3 s.234
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    • pp.376-383
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    • 2005
  • In the paper we investigate characteristics of a transitional behavior from a premixed flame to a triple flame in a lifted flame according to the change of equivalence ratio. In previous study, we showed that the stabilized laminar lifted flame regime is categorized by regimes of premixed flame, triple flame and critical flame. A gas-chromatograph is used to measure concentration field, a smoke-wire system is used to measure streak line, and a PIV system is used to measure velocity field in lifted flame. In the visualization experiment of smoke wire, the flow divergence and redirection reappeared in premixed flame as well as triple flame. Thus we cannot express the flame front of lifted flame has a behavior of triple flame with only flow divergence and redirection. In PIV measurement, flow velocity for those three flames has minimum value at the tip of flame front. To differentiate triple flame and premixed flame, $\Phi$ value of partially premixed fraction is employed. The partially premixed fraction $\Phi$ was constant in premixed flame. In critical flame small gradient appears over the whole regime. In triple flame, typical diffusion flame shape is obtained as parabolic distribution type due to diffusion flame trailing.

A Transitional Behavior of a Premixed Flame and a Triple Flame in a Lifted Flame(I) (부상화염에서 예혼합화염과 삼지화염의 천이적 거동(I))

  • Jang Jun Young;Park Jeong;Kim Tae Kwon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.3 s.234
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    • pp.368-375
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    • 2005
  • We have presented characteristics of a transitional behavior from a premixed flame to a triple flame in a lifted flame according to the change of equivalence ratio. The experimental apparatus consisted of a slot burner and a contraction nozzle for a lifted flame. As concentration difference of the both side of slot burner increases, the shape of flame changed from a premixed flame to a triple flame, and the liftoff height decreased to the minimum value and then increased again. Around this minimum point, it is confirmed a transition regime from premixed flame to triple flame. Consequently, the experimental results of the liftoff height, flame curvature, and luminescence intensity showed that the stabilized laminar lifted flame regime is categorized by regimes of premixed flame, triple flame and critical flame.

Characteristics of Premixed Flames in a Double Concentric Burner (이중 동축류 버너에서의 예혼합화염 특성에 관한 연구)

  • Gwon, Seong-Jun;Cha, Min-Seok;Choe, Man-Su;Jeong, Seok-Ho
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.12
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    • pp.1662-1669
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    • 2000
  • Various flame types are observed in a double concentric burner by varying equivalence ratio and flow rates in each tube. Observed flame types include bunsen-type flame, ring-shaped flame, outer lifted flame, inner lifted flame, and oscillatory lifted flame, The doman of existence of various flames is mapped with equivalence ratio and annular jet velocity. Each flame is investigated through direct photography and OH PLIF. As central air velocity increase, the blowout region is diminished and lifted oscillating flames are observed. Inner lifted flames are observed from bunsen flames or rich shaped flames by increasing central air velocity. For inner lifted flames, annular jet velocity, at flame liftoff decreases with increasing central air jet velocity. Axial velocity profile and temperature fie이 using LDV and CRS, respectively, for a typical inner lifted flame are also measured through which the role of tribrachial flame for stabilization in emphasized.

The Periodic Motion of Lifted Flames in Inverse Coflow Jets (역확산화염에서 부상 상태의 진동현상에 관한 연구)

  • Won, Jang-Hyeok;Seo, Jeong-Il;Bae, Soo-Ho;Shin, Hyun-Dong
    • 한국연소학회:학술대회논문집
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    • 2006.10a
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    • pp.73-78
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    • 2006
  • The lifted oscillating flame has been studied using experiments of inverse diffusion flames that the air jet injected into a methane background. To find out the characteristics of inverse diffusion flames, fundamentally flame stabilized diagram is investigated with various air and fuel jet velocities. It has five regions - flame extinction, stable attached flame, anchored flame, liftoff flame and blow off region. In inverse diffusion flame, lifted flames were observed near the blow off region. As long as flames lift off, flames oscillate by periods. In this oscillating lifted flame region, the frequency of 1 and under were observed in various air and methane jet velocities. Characteristics of lifted flames are also examined by using the ICCD direct image. And intensity of flame chemiluminescence is very different in rising and falling period from photographs. For the present, it is predicted that the changes of flame structure are related with flame oscillation, but more experiments will be needed to make clear the phenomenon.

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Buoyancy Effect on Stable and Oscillating Lifted Flames in Coflow Jets for Highly Diluted Propane (질소희석된 프로판 동축류 버너에서 부상화염에 대한 부력효과)

  • Kim, Jun-Hong;Shin, Moo-Kyung;Chung, Suk-Ho
    • 한국연소학회:학술대회논문집
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    • 2001.06a
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    • pp.9-16
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    • 2001
  • When large size nozzle with low jet velocity is used, the buoyancy effect arises from the density difference among propane, air, and burnt gas. Flame characteristics in such buoyant jets have been investigated numerically to elucidate the effect of buoyancy on lifted flames. It has been demonstrated that the cold jet has circular cone shape since upwardly injected propane jet decelerates and forms stagnation region. In contrast to the cold flow, the reacting flow with a lifted flame has no stagnation region by the buoyancy force induced from the burnt gas. To further illustrate the buoyancy effect on lifted flames, the reacting flow with buoyancy is compared with non-buoyant reacting flow. Non-buoyant flame is stabilized at much lower height than the buoyant flame. At a certain range of fuel jet velocities and fuel dilutions. an oscillating flame is demonstrated numerically showing that the height of flame base and tip vary during one cycle of oscillation. Under the same condition. non-buoyant flame exhibits only steady lifted flames. This confirms the buoyancy effect on the mechanism of lifted flame oscillation.

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Mechanism of Lifted Flames in Coflow Jet with Diluted Methane (질소희석된 메탄 동축류 제트에서 화염 부상 메커니즘에 관한 연구)

  • Hong, Ki-Jung;Won, Sang-Hee;Kim, Jun-Hong;Chung, Suk-Ho
    • 한국연소학회:학술대회논문집
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    • 2003.12a
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    • pp.177-184
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    • 2003
  • Stabilization mechanism of lifted flame in the near field of coflow jets has been investigated experimentally and numerically for methane fuel diluted with nitrogen. Lifted flames were observed only in the near field of coflow jets until blowout occurred in the normal gravity condition. To elucidate the stabilization mechanism for the stationary lifted flames in the near field of coflow jets for the diluted methane having the Schmidt number smaller than unity, the behaviors of the stationary lifted flame in microgravity and unsteady propagation phenomena were investigated numerically at various conditions of jet velocity. It has been founded that the buoyancy plays an important role for flame stabilization of lifted flame in normal gravity and the stabilization mechanism is due to the significant variation of the propagation speed of lifted flame edge compared to the local flow velocity at the edge.

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Study on the Turbulent Edge Propagation Speed of a Lifted Diffusion Flame in Turbulent Mixing Layer (난류 혼합층 확산화염에서 부상선단의 난류전파속도에 대한 연구)

  • Kim, Jun-Hong;Chung, S.H.;Ahn, K.Y.;Kim, J.S.
    • 한국연소학회:학술대회논문집
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    • 2004.11a
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    • pp.55-61
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    • 2004
  • Leading front of a lifted diffusion flame in turbulent mixing layer was investigated in order to find a appropriate definition of the turbulent edge propagation speed. The turbulent lifted diffusion flame was simulated by employing the flame hole dynamics combined with level-set method which yields a temporally evolving turbulent extinction process. By tracing the leading front locations of the temporal flame edges, temporal variations of the liftoff height, local flow velocity, and edge propagation speed at the leading front were investigated and they demonstrated the flame-stabilization condition of the turbulent lifted flame. Finally, a turbulent edge propagation speed was defined and its temporal variation from the simulation was discussed.

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Experimental Study on Laminar Lifted Methane Jet Flame Diluted with Nitrogen and Helium

  • Sapkal, Narayan;Lee, Won June;Park, Jeong;Kwon, Oh Boomg
    • 한국연소학회:학술대회논문집
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    • 2014.11a
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    • pp.387-389
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    • 2014
  • Laminar lifted methane jet flame diluted with nitrogen and helium in co-flow air has been investigated experimentally. This paper examines the role of chemistry, intermediate species responsible for stabilization of lifted flame. To elucidate the stabilization mechanism in lifted methane jet flames with Sc<1, the chemiluminescence intensities of $CH^*$ and $OH^*$ were measured using ICCD camera at various nozzle exit velocities and fuel mole fractions. It has been observed that the $OH^*$ species can play an important role in stabilization of lifted methane jet flame as they are good indicators of heat release rate which can affect on flame speed and increase stability through reduction in ignition delay time.

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Experimental Study on Laminar Lifted Methane Jet Flame Diluted with Nitrogen and Helium

  • Sapkal, Narayan;Lee, Won June;Park, Jeong;Kwon, Oh Boomg
    • 한국연소학회:학술대회논문집
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    • 2014.11a
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    • pp.125-128
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    • 2014
  • Laminar lifted methane jet flame diluted with nitrogen and helium in co-flow air has been investigated experimentally. This paper examines the role of chemistry, intermediate species responsible for stabilization of lifted flame. To elucidate the stabilization mechanism in lifted methane jet flames with Sc<1, the chemiluminescence intensities of $CH^*$ and $OH^*$ were measured using ICCD camera at various nozzle exit velocities and fuel mole fractions. It has been observed that the $OH^*$ species can play an important role in stabilization of lifted methane jet flame as they are good indicators of heat release rate which can affect on flame speed and increase stability through reduction in ignition delay time.

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A Study on the Mixing Capacity of Lifted Flame by the Nozzle Hole-tone of High Frequency in Non-premixed Jet Flames (비예혼합 제트화염에서 고주파수의 노즐 구멍음에 의한 부상화염 혼합성능에 관한 연구)

  • Jo, Joon-Ik;Lee, Kee-Man
    • Journal of the Korean Society of Visualization
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    • v.9 no.4
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    • pp.35-40
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    • 2011
  • An experimental investigation of the characteristic of non-premixed lifted flames with nozzle hole-tone of high-frequency has been performed. Before the fuel was supplied to nozzle, the fuel was supplied through a burner cavity which was located under the nozzle. The fuel passed through the excitation cavity under the influence of the high-frequency affects the lifted flame characteristics. The measurements were performed in flow range that occurs lifted flame and blow out. When the high-frequency is generated from burner cavity, the lifted length became shorter, and noise reduced comparing to unexcitation case. Additionally, operating flow range was increased and diameter of flame base became smaller with high-frequency effect. Through this experiments, it's ascertained that the high-frequency excitation can be adopted with effective method for flame stability and noise reduction.