• Title/Summary/Keyword: turbulent burning velocity

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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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Structure of Turbulent Premixed Opposed Impinging Jet Flame with Simultaneous PIV/OH PLIF Measurements (PIV/OH PLIF 동시측정을 이용한 난류 대향 분출 예혼합화염 구조 연구)

  • Cho, Yong-Jin;Kim, Ji-Ho;Cho, Tae-Young;Yoon, Young-Bin
    • Journal of the Korean Society of Combustion
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    • v.8 no.1
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    • pp.36-45
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    • 2003
  • The subject of turbulent premixed flames has been focused by many researchers for a number of decades. Especially, Borghi suggested a magnificent diagram classifying turbulent combustion areas and Lipatnikov and Chomiak modified this diagram. Recently, experimental techniques have been developed so that we can use PIV for measuring 2D velocity field and apply OH PLIF techniques for obtaining flame locations. In present study, a new diagram is proposed using strain rates and OH signal intensity. Thus, simultaneous PIV and OH PLIF measurements are used for shear strain rates and flame locations, respectively. It is believed that the shear strain rates represent flow characteristics such as turbulence intensity and the OH intensity indicates the flame characteristics such as burning velocities.

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A Discussion of Combustion Regime Based on Laser Tomography and Flame Structure Diagram (레이저 토모그래피와 화염구조선도에 의한 연소영역의 검토)

  • Kim, J.H.
    • Journal of Power System Engineering
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    • v.2 no.1
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    • pp.17-24
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    • 1998
  • The combustion regime was discussed using a laser tomography and flame structure diagram. It was shown first how to represent the turbulent burning velocity and flame structural parameters in the dimensionless plane referred to as the flame structure diagram. And then, turbulent flame structure from the obtained images by laser tomography was compared with combustion regime in the Re-Da plane, one of the diagrams, specified by different researchers. As the result, the $u'/S_{L0}$ ratio at the boundary between the wrinkled laminar flame regime and reactant islands flame regime was found to be about 1.5.

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Effect of Oxygen Enriched Air on the Combustion Characteristics in a Coaxial Non-Premixed Jet ( I ) - Lift-off and Flame Stability - (산소부화공기가 동축 비예혼합 제트의 연소특성에 미치는 영향 (I) - 화염의 부상과 안정성)

  • Kwark, Ji-Hyun;Jeon, Chung-Hwan;Chang, Young-June
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.2
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    • pp.160-166
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    • 2004
  • Combustion using oxygen enriched air is known as a technology which can increase flame stability as well as thermal efficiency due to improving the burning rate. Lift-off, blowout limit and flame length were examined as a function of jet velocity, coflow velocity and OEC(Oxygen Enriched Concentration). Blowout limit of the flame below OEC 25% decreased with increase of coflow velocity, but the limit above OEC 25% increased inversely. Lift-off height decreased with increase of OEC. In particular, lift-off hardly occurred in the condition above OEC 40%. Flame length of the flames above OEC 40% was increased until the blowout occurred. Great flame stability was obtained since lift-off and blowout limit significantly increased with increase of OEC.

Lift-off and Flame Stability of a Coaxial Non-Premixed Jet Using Oxygen Enriched Air (산소부화공기를 이용한 동축 제트화염의 부상과 연소 안정성)

  • Kwark, Ji-Hyun;Jeon, Chung-Hwan;Chang, Young-June
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.326-331
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    • 2003
  • Combustion using oxygen enriched air is known as a technology which can increase flame stability as well as thermal efficiency due to improvement of the burning rate. Lift-off, blowout limit and flame length were examined as a function of jet velocity, coflow velocity and OEC(Oxygen Enriched Concentration). Blowout limit of the flame below OEC 25% decreased with coflow velocity, but the limit above OEC 25% increased inversely. Lift-off height decreased with increase of OEC. Especially lift-off hardly occurred in the condition above OEC 40%. Flame length of the flames above OEC 40% was increased until the blowout occurred. Flame stability became improved since lift-off and blowout limit increased much with increase of OEC.

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An Experimental Study on Structure of Twin-Fluid Spray with Air Entrainment (공기 유입을 고려한 2유체 분무의 구조에 관한 실험적 연구)

  • Chae, Hyo-Cheol;Kim, Dong-Il;Oh, Sang-Heun
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.925-930
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    • 2000
  • This paper is investigated the entrainment of air into sprays which has significant effects on the combustion efficiency, stability of flame using the air-assisted twin-fluid nozzle in non-burning. The factors which may be expected to affect the entrainment of air by a liquid spray are: Relative velocity of droplet and ambient gas; Drop size and size distribution; Density and other property of the liquid. Here, axial, radial velocity and turbulent kinetic energy of spray droplet was measured with the PIV(Particle Image Velocimetry). Spray characteristics were also visualized using CCD camera. The results indicate that the entrainment rate increases more or less non-linearly with the downstream region.

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The effect of Volume Expansion on the Propagation of Wrinkled Laminar Premixed Flame

  • Chung, E.H.;Kwon, Se-Jin
    • 한국연소학회:학술대회논문집
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    • 1998.10a
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    • pp.139-154
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    • 1998
  • Under certain circumstance, premixed turbulent flame can be treated as wrinkled thin laminar flame and its motion in a hydrodynamic flow field has been investigated by employing G-equation. Past studies on G-equation successfully described certain aspects of laminar flame propagation such as effects of stretch on flame speed. In those studies, flames were regarded as a passive interface that does not influence the flow field. The experimental evidences, however, indicate that flow field can be significantly modified by the propagation of flames through the volume expansion of burned gas. In the present study, a new method to be used with G -equation is described to include the effect of volume expansion in the flame dynamics. The effect of volume expansion on the flow field is approximated by Biot-Savart law. The newly developed model is validated by comparison with existing analytical solutions of G -equation to predict flames propagating in hydrodynamic flow field without volume expansion. To further investigate the influence of volume expansion, present method was applied to initially wrinkled or planar flame propagating in an imposed velocity field and the average flame speed was evaluated from the ratio of flame surface area and projected area of unburned stream channel. It was observed that the initial wrinkling of flame cannot sustain itself without velocity disturbance and wrinkled structure decays into planar flame as the flame propagates. The rate of decay of the structure increased with volume expansion. The asymptotic change in the average burning speed occurs only with disturbed velocity field. Because volume expansion acts directly on the velocity field, the average burning speed is affected at all time when its effect is included. With relatively small temperature ratio of 3, the average flame speed increased 10%. The combined effect of volume expansion and flame stretch is also considered and the result implied that the effect of stretch is independent of volume release.

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A study on the heat transfer of the turbocharged gasoline engine (터보과급 가솔린기관의 열전달에 관한 연구)

  • 최영돈;홍진관
    • Journal of the korean Society of Automotive Engineers
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    • v.10 no.5
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    • pp.69-82
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    • 1988
  • Heat transfer experiment is carried out during the performance test of the 4-cylinder 4-stroke cycle turbo-charged gasoline engine. Cycle simulation employing the measured pressure in cylinder, the cooling water temperature and flow rate and others is carried out in order to calculate the gas temperature in cylinder. In this simulation combustion process was simulated by Annand's two zone model and suction, compression, and other processes are calculated completely. From this simulation, we can obtain not only the heat transfer coefficient but also the flame speed, turbulent burning velocity, flame factor and the boiling condition of cooling passage. The results are investigated with engine speed, equivalence ratio and spark advance.

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A Study for the Advanced Design of Rotary Kiln Incinerator III : 3-Dimensional CC1$_4$/CH$_4$Gas-phase Turbulent Reaction Model (로타리 킬른 소각로 고도 설계를 위한 연구 III : 3차원 CC1$_4$/CH$_4$기상난류 반응 모델)

  • 엄태인;장동순;채재우
    • Journal of Energy Engineering
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    • v.2 no.1
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    • pp.54-67
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    • 1993
  • Two turbulent reaction models of the premixed CC1$_4$/CH$_4$/air mixture are successfully incorporated in a 3-dimensional computer program and is applied for Dow Chemical incinerator equipped with two main off-center burners. The first reaction model is fast chemistry model(model 1), in which chemical reaction is governed by the turbulent mixing itself. And the second one is nonequilibrium model(model 2), where the effect of the chemical kinetics due to the presence of CC1$_4$is considered by the incorporation of the burning velocity data of CC1$_4$. The second model not only shows the flame inhibition trend due to the presence CC1$_4$compound, but also predicts qualitatively the vortical stratification of the CC1$_4$concentration appeared experimentally at the kiln exit. Other comparisions of two models are made in detail.

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Effect of Diluents and Oxygen-Enrichness on the Stability of Nonpremixed Flame (산소부화와 희석제에 따른 비예혼합 화염의 안정성)

  • 배정락;이병준
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.10
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    • pp.1458-1464
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    • 2002
  • $CO_2$ is well known greenhouse gas which is the major source of global warming. Reducing $CO_2$ emission in combustion process can be achieved by increasing combustion efficiency, oxygen enriched combustion and recirculation of the emitted $CO_2$ gas. Stability of non-premixed flame in oxygen enriched environment will be affected by the amount of oxygen, kind of diluents and fuel exit velocity. The effects of these parameters on flame liftoff and blowout are studied experimentally oxidizer coflowing burner. Experiments were divided into three cases according as where $CO_2$gas was supplied. - 1) to coflowing air, 2) to fuel with 0$_2$-$N_2$ coflow, 3) to coflowing oxygen. Flame in air coflowing case was lifted in turbulent region. Flame lift and blowout in laminar region with the increase in $CO_2$ volume fraction in $CO_2$-Air mixture makes flame lift and blowout in laminar region. Increase in oxygen volume fraction makes flame stable-i.e. flame liftoff and blowout occur at higher fuel flowrates. Liftoff height was non-linear function of nozzle exit velocity and affected by the $O_2$ volume fraction. It was found that the flame in $O_2$-$N_2$ coflow case was more stable than $O_2$-$CO_2$ case, Liftoff heights vs (nozzle exit velocity/laminar burning velocity)$^{3.8}$ has a good correlation in $O_2$-$CO_2$ oxidizer case.