• Title/Summary/Keyword: Flame displacement

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Roles of displacement speed of premixed flame embedded in isotropic turbulent decaying flow (직접수치해법을 이용한 난류 예혼합 화염전파속도 연구)

  • Han, In-Suk;Huh, Kang-Yul
    • 한국연소학회:학술대회논문집
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    • 2006.10a
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    • pp.177-186
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    • 2006
  • Flame surface area is a critical parameter determining turbulent flame speed. Three-dimensionaldirect numerical simulations (DNS) were conducted to figure out the evolution process of flame surface area. Fully compressible Navier-Stokes equations are solved to reproduce premixed flame embedded in isotropic decaying turbulent flow. The tangential straining and curvature of propagating surface affect development of flame area. In this study, four different turbulent intensity flows and three different Le number flames are investigated to force changes in straining and curvature effects. Consistent results are obtained for the probability density functions (PDF) of strain and curvature with previous researches. It is revealed that displacement speed, which is a speed of flame surface relative to unburnt flow, controls the balance between sink and source of flame surface area.

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Roles of Displacement Speed of Premixed Flame Embedded in Isotropic Turbulent Decaying Flow (직접수치해법을 이용한 난류 예혼합 화염전파속도 연구)

  • Han, In-Suk;Huh, Kang-Yul
    • Journal of the Korean Society of Combustion
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    • v.12 no.2
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    • pp.10-19
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    • 2007
  • Flame surface area is a critical parameter determining turbulent flame speed. Three-dimensional direct numerical simulations(DNS) were conducted to figure out the evolution process of flame surface area. Fully compressible Navier-Stokes equations are solved to reproduce premixed flame embedded in isotropic decaying turbulent flow. The tangential straining and curvature of propagating surface affect development of flame area. In this study, four different turbulent intensity flows and three different Le number flames are investigated to force changes in straining and curvature effects. Consistent results are obtained for the probability density functions (PDF) of strain and curvature with previous researches. It is revealed that displacement speed, which is a speed of flame surface relative to unburnt flow, controls the balance between sink and source of flame surface area.

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Experimental Studies on the Interactions between Propagating Flames and Different Multiple Obstacles in an Explosion Chamber with a L/D Ratio of 0.57 (0.57의 L/D 비를 가지는 폭발챔버에서 전파하는 화염과 다중 장애물의 상호작용에 관한 실험적 연구)

  • Park, Dal-Jae
    • Journal of the Korean Society of Safety
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    • v.27 no.6
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    • pp.70-77
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    • 2012
  • Experimental investigations were performed to examine the characteristics of propagating flame fronts around multiple bars within a rectangular chamber. The explosion chamber is 400 mm in height, $700{\times}700mm^2$ in cross-section and has a large top-venting area, $A_v$, of $700{\times}210mm^2$. This results in a value of 0.44 for $A_v/V^{2/3}$ and a L/D value of 0.57. The multiple obstacles of length 700 mm with a blockage ratio of 30 % were placed within the chamber. Temporally resolved flame front images were recorded by a high speed video camera to investigate the interaction between the propagating flame and the obstacles. Results showed that the flame propagation speeds before the flame impinges onto the obstacle almost equal to the laminar burning velocity. As the propagating flame impinged on the obstacle, the central region of flame began to become concave, this resulted in the flame deceleration in the region. As the flame interacted with the modified flow filed generated behind the central obstacle, the probability density functions(PDFs) of the local flame displacement speed were extensively distributed toward higher speeds.

Interactions Between a Propagating Flame and Rectangular Wall Obstacles in a Rectangular Confinement (직사각형 폭발 챔버에서 화염전파와 직사각형 장애물의 상관관계)

  • Park, Dal-Jae;Lee, Tae-Sung;Lee, Young-Soon
    • Journal of the Korean Society of Safety
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    • v.23 no.2
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    • pp.81-86
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    • 2008
  • Experimental studies have been performed to examine the influences of wall obstructions in a rectangular confinement. Three wall obstacles with blockage ratios ranging from 10 to 30% were used. Temporally resolved flame front images were recorded by a high-speed video camera to investigate the interaction between a propagating flame and the obstacle. The local flame displacement speed and its probability density functions(PDFs) were obtained for the wall obstructions. During the interaction with the sharp-edges of the wall obstacles, the local propagation speed increased. The increase of local speed became larger as the obstruction ratio increased. However, the averaged flame displacement speeds with different blockage ratios were not significantly different within the chamber as shown in the paper of Park et al. The flame front interaction investigated in this work was less dependent of the obstacle obstructions compared to that published in the literature for large L/D.

Interactions between Propagating Flame Fronts and Obstacles in an Explosion Chamber with a H/L Ratio of 0.86

  • Park, Dal Jae
    • Journal of the Korean Institute of Gas
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    • v.17 no.1
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    • pp.13-18
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    • 2013
  • Experimental studies were carried out to investigate the interactions between the propagating flame fronts and different multiple obstacles within an explosion chamber. The explosion chamber is 600 mm in height, $700{\times}700mm^2$ in cross-section and has a H/L value of 0.86. Three different multiple obstacles with the blockage ratio of 0.43 were replaced within the chamber. The results showed that relatively higher local flame displacement speed was observed with the triangular obstacle while the lower was observed with the circular one. It was found that the local flame displacement speeds behind the obstacle were largely dependent on the obstacle types. It was also found that as the flame interacted with the flow field generated behind the obstacle, the probability density functions(PDFs) of the local flame displacement speed were extensively distributed toward higher speeds.

Characteristics of Propagating Tribrachial Flames in Counterflow

  • Ko, Young-Sung;Chung, Tae-Man;Chung, Suk-Ho
    • Journal of Mechanical Science and Technology
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    • v.16 no.12
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    • pp.1710-1718
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    • 2002
  • The effect of fuel concentration gradient on the propagation characteristics of tribrachial (or triple) flames has been investigated experimentally in both two-dimensional and axisymmetric counterflows. The gradient at the stoichiometric location was controlled by the equivalence ratios at the two nozzles; one of which is maintained rich, while the other lean. Results show that the displacement speed of tribrachial flames in the two-dimensional counterflow decreases with fuel concentration gradient and has much larger speed than the maximum speed predicted previously in two-dimensional mixing layers. From an analogy with premixed flame propagation, this excessively large displacement speed can be attributed to the flame propagation with respect to burnt gas. Corresponding maximum speed in the limit of small mixture fraction gradient was estimated and the curvefit of the experimental data substantiates this limiting speed. As mixture fraction gradient approaches zero, a transition occurs, such that the propagation speed of tribrachial flame approaches stoichiometric laminar burning velocity with respect to burnt gas. Similar results have been obtained for tribrachial flames propagating in axisymmetric counterflow.

A Numerical Study of the Flame Cell Dynamics in Opposed Nonpremixed Tubular Configuration (비예혼합 튜브형상내 화염셀의 거동에 대한 수치 해석적 연구)

  • Park, Hyunsu;Yoo, Chun Sang
    • 한국연소학회:학술대회논문집
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    • 2014.11a
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    • pp.175-178
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    • 2014
  • The flame cell dynamics in 2-D opposed nonpremixed tubular configuration was investigated using high-fidelity numerical simulations. The diffusive-thermal instability occurs as the $Damk{\ddot{o}}hler$ number, Da, approaches the 1-D extinction limit of the tubular flames and several flame cells are generated depending on Da, and flame radius. In general, the number of flame cells are found close to the largest wave number from the linear stability analysis. It was also found from the displacement speed analysis that during the local flame extinction and cell formation, negative edge flame speed is observed due to small gain from reaction compared to large loss from diffusion.

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2-Dimensional Visualization of the Flame Propagation in a Four-Valve Spark-Ignition Engine (가솔린엔진에서의 2차원 화염 가시화)

  • Bae, Choong-Sik
    • Journal of the Korean Society of Combustion
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    • v.1 no.1
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    • pp.65-73
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    • 1996
  • Flame propagation in a four-valve spark-ignition optical engine was visualized under lean-bum conditions with A/F=18 at 2000rpm. The early flame development in a four-valve pentroof-chamber single-cylinder engine was examined with imaging of the laser-induced Mie scattered light using an image-intensified CCD camera. Flame profiles along the line-of-sight were also visualized through a quartz piston window. Two-dimensional flame structures were visualized with a Proxitronic HF-1 fast motion camera system by Mie scattering from titanium dioxide particles along a planar laser sheet generated by a copper vapor laser. The flame propagation images were subsequently analysed with an image processing programme to obtain information about the flame structure under different tumble flow conditions generated by sleeved and non-sleeved intake ports. This allowed enhancement of the flame images and calculation of the enflamed area, and the displacement of its center, as a function of the tumble flow induced by the pentroof-chamber in the vicinity of spark plug. Image processing of the early flame development quantified the correlation between flame and flow characteristics near the spark plug at the time of ignition which has been known to be one of the most important factors in cyclic combustion variations in lean-burn engines. The results were also compared with direct flame images obtained from the natural flame luminosity of the lean mixture.

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Numerical analysis on the rapid fire suppression using a water mist nozzle in a fire compartment with a door opening

  • Lee, Jaiho
    • Nuclear Engineering and Technology
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    • v.51 no.2
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    • pp.410-423
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    • 2019
  • Fire suppression using a water mist nozzle directly above an n-Heptane pool in a fire compartment with a door opening was numerically investigated using the Fire Dynamics Simulator (FDS) for the purpose of application in nuclear power plants. Input parameters for the numerical simulation were determined by experimental measurements. Water mist was activated 10 s after the fire began. The sensitivity analysis was conducted for three input parameters: total number of cubic cells of 6032-2,926,400, droplets per second of 1000-500,000, and extinguishing coefficient of 0-100. In a new simple calibration method of this study, the extinguishing coefficient yielding the fire suppression time closest to that measured by experiments was found for use as the FDS simulation input value. When the water mist jet flow made contact with the developed fire, the heat release rate instantaneously increased, and then rapidly decreased. This phenomenon occurred with a displacement of the flame near the liquid fuel pool. Changing the configuration of the door opening with different aspect ratios and opening ratios had impact on the maximum value of the heat release rate due to the flame displacement.

Experimental Studies on the Interaction Between a Propagating Flame and Multiple Obstacles in a Rectangular Chamber

  • Park, Dal-Jae;Ahn, Jeong-Jin;Lee, Young-Soon
    • Journal of the Korean Institute of Gas
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    • v.12 no.1
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    • pp.54-61
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    • 2008
  • Experimental investigations were performed to assess the influences of different multiple obstacles on flame propagation in a rectangular confinement. Three different multiple obstacles were used: circular, triangular and square cross-sections with blockage ratios of 15% and 30%. The same method described in Park et al. [13] to investigate the interaction between the propagating flame and the obstacle was applied. Before the freely propagating flame impinged on the obstacle, the flame propagation speed remains close to the laminar burning velocity, regardless of the obstacles used. The reported data revealed that the trend in increase of the local flame propagation speed is a result of the interaction between the obstacle and the propagating flame front behind the obstacle. The local speed was found to increase from a circular to a triangular and a square obstacle. The mean flame speed was found to be less dependent on both the obstacle types and the different blockage ratios used.

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