• Title/Summary/Keyword: Flame Structure

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A Study on the Structure of Premixed Turbulent Propagating Flames Using a Microprobe Method (정전탐침법에 의한 예혼합 난류전파화염의 구조에 관한 연구)

  • Kim, J.H.;Ahn, S.K.
    • Transactions of the Korean Society of Automotive Engineers
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    • v.3 no.6
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    • pp.78-86
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    • 1995
  • The structure of premixed turbulent flames in a constant-volume vessel was investigated using a microprobe method. The flame potential signal having one to eight peaks was detected in the case of turbulent flames, each of them being regarded as a flamelet existing in the flame zone. Based on this consideration, the flame propagation speed, the thickness of the flame zone, the number of flamelets and the separation distance between adjacent flamelets in the flame zone were measured. The experimental resuits of this work suggest the existence of "reactant islands" behind the flame front when the turbulence was intensified to some extent. The critical(lowest) ratio of turbulence intensity to the laminar burning velocity being found to be about 0.7 for the formation of reactant islands in this experiment.

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A Numerical Study on the Lean-Rich Interaction of Methane/Air Flames (희박-과농 메탄 화염의 상호작용에 관한 수치해석적 연구)

  • Lee, Seung-Dong;Jeong, Seok-Ho
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.1
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    • pp.377-383
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    • 1996
  • Interaction of flames in a lean-rich concentration field is studied numerically adopting a counterflow as a model problem. Detailed kinetic mechanism is adopted in analyzing the structure of various type of flames which can be found in lean-rich interaction. Flow field is simplified to quasi one-dimensional by using boundary layer approximation and similarity formulation. Triple flames are identified and its structure shows that a diffusion flame is located in the middle of two premixed flames. Such a diffusion flame is formed by $H_2$ and CO generated from the rich premixed flame and $O_2$ leaked from the lean premixed flame. The flame position can be identified either from the hydrogen production rate or the heat release rate. Transition from single diffusion flame to triple flame is observed as degree of premixing is increased.

Structure of Edge Flame in a Methane-Oxygen Mixing Layer (메탄/순산소 혼합층에서 edge flame의 구조)

  • Choi, S.K.;Kim, J.;Chung, S.H.;Kim, J.S.
    • 한국연소학회:학술대회논문집
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    • 2006.04a
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    • pp.149-156
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    • 2006
  • Structure of edge flame established in a mixing layer, formed between two uniformly flowing pure $CH_4$ and pure $O_2$ streams, is numerically investigated by employing a detailed methane-oxidation mechanism. The numerical results exhibited the most outstanding distinction of using pure oxygen in the fuel-rich premixed-flame front, through which the carbon-containing compound is found to leak mainly in the form of CO instead of HC compounds, contrary to the rich $CH_4-air$ premixed flames in which $CH_4$ as well as $C_2H_m$ leakage can occur. Moreover, while passing through the rich premixed flame, a major route for CO production, in addition to the direct $CH_4$ decomposition, is found to be $C_2H_m$ compound formation followed by their decomposition into CO. Beyond the rich premixed flame front, CO is further oxidized into $CO_2$ in a broad diffusion-flame-like reaction zone located around moderately fuel-rich side of the stoichiometric mixture by the OH radical from the fuel-lean premixed-flame front. Since the secondary CO production through $C_2H_m$ decomposition has a relatively strong reaction intensity, an additional heat-release branch appears and the resulting heat-release profile can no longer be seen as a tribrachial structure.

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Structure of Edge Flame in a Methane-Oxygen Mixing Layer (메탄/순산소 혼합층에서 Edge Flame의 구조)

  • Choi, S.K.;Kim, J.;Chung, S.H.;Kim, J.S.
    • Journal of the Korean Society of Combustion
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    • v.11 no.1
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    • pp.19-26
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    • 2006
  • Structure of edge flame established in a mixing layer, formed between two uniformly flowing pure $CH_4$ and pure $O_2$ streams, is numerically investigated by employing a detailed methane-oxidation mechanism. The numerical results exhibited the most outstanding distinction of using pure oxygen in the fuel-rich premixed-flame front, through which the carbon-containing compound is found to leak mainly in the form of CO instead of HC compounds, contrary to the rich $CH_4-air$ premixed flames in which $CH_4$ as well as $C_2H_m$ leakage can occur. Moreover, while passing through the rich premixed flame, a major route for CO production, in addition to the direct $CH_4$ decomposition, is found to be $C_2H_m$ compound formation followed by their decomposition into CO. Beyond the rich premixed flame front, CO is further oxidized into $CO_2$ in a broad diffusion-flame-like reaction zone located around moderately fuel-rich side of the stoichiometric mixture by the OH radical from the fuel-lean premixed-flame front. Since the secondary CO production through $C_2H_m$ decomposition has a relatively strong reaction intensity, an additional heat-release branch appears and the resulting heat-release profile can no longer be seen as a tribrachial structure.

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Radiation Effects on the Flame Structure and Extinction Limit of Counterflow Partially Premixed Methane Flames Diluted with Water Vapor in the Air Stream (공기류측에 수증기가 첨가된 대향류 메탄 부분예혼합화염의 화염구조 및 소화한계에 미치는 복사효과)

  • Park, Ji-Woong;Oh, Chang Bo;Kim, Ook Joong
    • 한국연소학회:학술대회논문집
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    • 2012.11a
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    • pp.325-328
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    • 2012
  • Radiation effects on the partially premixed methane flames diluted with water vapor in the air stream were numerically investigated. OPPDIF code and GRI-v3.0 were used in the numerical simulation. Adiabatic condition was compared with two different radiation models, optically-thin and WSGGM models. It was found that the radiation effect on the flame structure for the equivalence ratio (${\Phi}$) of 2.5 was less than ${\Phi}=1.5$. Extinction limit was not affected significantly, however, local flame structure was markedly influenced by the radiation models as increasing the water vapor concentration.

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Behavior of the Coherent Structure on the Attached Forced Flame (가진된 부착화염에서 거대와동의 거동)

  • Kim, Dae-Won;Lee, Kee-Man
    • Journal of Advanced Marine Engineering and Technology
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    • v.33 no.2
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    • pp.259-266
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    • 2009
  • An experimental study was conducted to investigate the effects of forcing amplitude on the flow structure near the nozzle exit of forced jet diffusion flames. The jet was excited up to the blowout occurrence by a considerable large amplitude with a periodic velocity fluctuation at the tube resonating frequency. In the attached flame regime, we disclosed the very interesting result newly that adding of a moderate forcing amplitude caused the jet flame to become longer in spite of being forced. Particular attention is focused on the turnabout mechanism of vortex roll-up around the elongated flame, which has not been reported previously, and on the inner coherent structure of the forced jet in the attached flame regime. From the velocity and flow visualization results, it was ascertained that the surrounding air due to the occurrence of negative velocity parts was suck into the fuel nozzle. To aid in understanding the rotating phenomenon of coherent structure, we present a schematic diagram of the turnabout mechanism of vortex roll-up. The mechanism of vortex turnabout phenomenon can be easily understood by considering the positive and negative velocity amplitudes about the instantaneous velocity of the forcing flow, as shown in this diagram.

PSR-Based Microstructural Modeling for Turbulent Combustion Processes and Pollutant Formation in Double Swirler Combustors

  • Kim, Yong-Mo;Kim, Seong-Ku;Kang, Sung-Mo;Sohn, Jeong-Lak
    • Journal of Mechanical Science and Technology
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    • v.15 no.1
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    • pp.88-97
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    • 2001
  • The present study numerically investigates the fuel-air mixing characteristics, flame structure, and pollutant emission inside a double-swirler combustor. A PSR(Perfectly Stirred Reactor) based microstructural model is employed to account for the effects of finite rate chemistry on the flame structure and NO formation. The turbulent combustion model is extended to nonadiabatic flame condition with radiation by introducing an enthalpy variable, and the radiative heat loss is calculated by a local, geometry-independent model. The effects of turbulent fluctuation are taken into account by the joint assumed PDFs. Numerical model is based on the non-orthogonal body-fitted coordinate system and the pressure/velocity coupling is handled by PISO algorithm in context with the finite volume formulation. The present PSR-based turbulent combustion model has been applied to analyze the highly intense turbulent nonpremixed flame field in the double swirler combustor. The detailed discussions were made for the flow structure, combustion effects on flow structure, flame structure, and emission characteristics in the highly intense turbulent swirling flame of the double swirler burner.

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Numerical Study on Flame Structure and NO Formation Characteristics in Oxidizer-Controlled Diffusion Flames (산화제 제어 확산화염의 화염구조 및 NO 생성 특성에 관한 수치해석적 연구)

  • Lee, Chang-Eon;Han, Ji-Ung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.5
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    • pp.742-749
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    • 2002
  • Numerical Study with detailed chemistry has been conducted to investigate the flame structure and NOx formation characteristics in oxygen -enhanced(CH$_4$/O$_2$-$N_2$) and oxygen-enhanced-EGR(CH$_4$/O$_2$-$CO_2$) counter diffusion flame with various strain rates. A small amount of $N_2$is included in oxygen-enhanced-EGR combustion, in order to consider the inevitable $N_2$contamination by $O_2$production process or air infiltration. The results are as follows : In CH$_4$/O$_2$-$CO_2$flame it is very important to adopt a radiation effect precisely because the effect of radiation changes flame structure significantly. In CH$_4$/O$_2$-$N_2$flame special strategy to minimize NO emission is needed because it is very sensitive to a small amount of $N_2$. Special attention is needed on CO emission by flame quenching, because of increased CO concentration. Spatial NO production rate of oxygen-enhanced combustion is different from that of air and oxygen-enhanced-EGR combustion in that thermal mechanism plays a role of destruction as well as production. In case CH$_4$/O$_2$-$CO_2$flame contains more than 40% $CO_2$it is possible to maintain the same EINO as that of CH$_4$/Air flame with accomplishing higher temperature than that of CH$_4$/Air flame. EINO decreases with increasing strain rate, and those effects are augmented in CH$_4$/O$_2$flame.

Flame Structure of a Liftoff Non-Premixed Turbulent Hydrogen Jet with Coaxial Air (부상된 수소 난류확산화염의 화염구조)

  • Oh, Jeong-Seog;Yoon, Young-Bin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.33 no.9
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    • pp.699-708
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    • 2009
  • To understand hydrogen jet liftoff height, the stabilization mechanism of turbulent lifted jet flames under non-premixed conditions was studied. The objectives were to determine flame stability mechanisms, to analyze coexistence of two different flame structure, and to characterize the lifted jet at the flame stabilization point. Hydrogen flow velocity varied from 100 to 300 m/s. Coaxial air velocity was changed from 12 to 20 m/s. Simultaneous velocity field and reaction zone measurements used, PIV/OH PLIF techniques with Nd:YAG lasers and CCD/ICCD cameras. Liftoff height decreased with the increase of fuel velocity. The flame stabilized in a lower velocity region next to the faster fuel jet due to the mixing effects of the coaxial air flow. The flame stabilization was related to turbulent intensity and strain rate assuming that combustion occurs where local flow velocity and turbulent flame propagation velocity are balanced. At the flame base, two different flame structures were found that was the partial premixed flames and premixed flame.

A Study on the Lifted Flame Structure with Strain Rates in Premixed Impinging Jet Flames of Syngas (H2/CO) (합성가스(H2/CO) 예혼합 충돌 제트화염에서 신장률에 따른 부상된 화염 구조에 관한 연구)

  • SIM, KEUNSEON;JANG, BYOUNGLOK;LEE, KEEMAN
    • Transactions of the Korean hydrogen and new energy society
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    • v.26 no.4
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    • pp.347-356
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    • 2015
  • A study has been conducted numerically to investigate the lifted flat syngas flame structure of impinging jet flame configuration with the global strain rates in 10% hydrogen content. In this study, the effects of strain rate were major parameters on chemistry kinetics and flame structure at stagnation point. The numerical results were calculated by SPIN application of the CHEMKIN package. The strain rates were adjusted with Reynolds numbers of premixed syngas-air mixture. Different flame shapes were observed with different strain rates. As strain rate has increased, the flame temperature and axial velocity have been decreased due to the flame heat loss increment, and the OH radical reaction zones become narrower but each mole fractions are still constant. Also, the reversion of $H_2O$ product near stagnation point has been found out when strain rate has increased. This phenomenon is attributed to the rapid production of oxidizing radical reaction such as the R12 ($H+O_2(+M)=HO_2(+M)$), which makes the R18 ($HO_2+OH=O_2+H_2O$) reaction increment.