• Journal of the Korean Society of Safety
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• v.20 no.2 s.70
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• pp.44-49
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• 2005

Real-scale experimental study was performed to characterize the surface flame propagating velocity along the OF cable in the underground utility fire. Temperatures of oil filled OF cable and dried OF cable with the diameter of 90mn were measured using thermocouple and data log system. The hexane and alkyl-benzene oil were used as a fire source using the ignition device. As a result while the surface flame propagating velocity of the three cables was $0.06\~0.09cm/s$, the surface flame propagating velocity of the one cable was $0.028\~0.032cm/s$. Therefore, it was found that the surface propagating flame velocity of the three OF cables is $2.1\~2.8times$ faster than that of one OF cable case. The results show that the surface propagating flame velocity became larger as increase of the number of cable, the volume of alkyl-benzene oil in the cable. The characteristics of surface propagating flame velocity in the OF cable can be helpful to fire suppression system in utility.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.8
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• pp.1061-1070
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• 2003

A triple flame in a mixing layer was studied experimentally with concentration gradient and mean velocity by using a multi-slot burner, which can stabilize the lift-off flame. Flame stabilization condition, lift-off heights, and some other characteristics were examined for methane and propane flame within a range of very low concentration gradient. Pitot-tube and LDV(Laser Doppler Velocimetry) were used for velocity. Mass spectroscopy and Rayleigh scattering signal were used for concentration gradients. Thermo-couples and SiC TFP(Thin Filament Pyrometer) were used for temperature. It was found that minimum values of the lift-off heights exist at a certain concentration gradient for constant mean velocity and this means that the propagation velocity has a maximum value. The scales of flame to the burner nozzle and intensity variation of the diffusion flame were suspected as the cause.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.2
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• pp.250-258
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• 2010

A numerical analysis of reactive flow in a liftoff flame is accomplished to elucidate the characteristics of flame propagation velocity and volume integral of reaction rate with the variation of nozzle diameter and fuel injection flow rate in a liftoff flame consisted with fuel rich region, fuel lean region and diffusion flame region. The increase of fuel injection velocity enhances flame propagation velocity for the selected three nozzle diameter(d=0.25, 0.30, 0.35mm), but its effect on the flame propagation velocity is not much greater than 4.3%. The increase of fuel flow rate is directly and linearly related with the volume reaction rate and so the volume reaction rate, not the flame propagation velocity, might be considered to accommodate the variation of fuel flow rate in a liftoff flame.

• Journal of the Korean Society of Combustion
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• v.13 no.4
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• pp.16-25
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• 2008

Experiments have been conducted to clarify impacts of curtain flow and velocity ratio on low strain rate flame extinction, and to further display transition of shrinking flame disk to flame-hole. Critical mole fractions at flame extinction are examined in terms of velocity ratio, global strain rate, and nitrogen curtain flow rate. It is shown that multi-dimensional effects at low strain rate flames through global strain rate, velocity ratio, and curtain flowrate dominantly contribute to flame extinction and transition of shrinking flame disk to flame hole. Our concerns are particularly focused on the dynamic behavior of an edge flame in shrinking flame disk.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.7
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• pp.477-485
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• 2009

The study of nitrogen dilution effect on the flame stability was experimentally investigated in a non-premixed turbulent lifted hydrogen jet with coaxial air. Hydrogen gas was used as a fuel and coaxial air was used to make flame liftoff. Each of hydrogen and air were injected through axisymetric inner and outer nozzles ($d_F=3.65\;mm$ and $d_A=14.1\;mm$). And both fuel jet and coaxial air velocity were fixed as $u_F=200\;m/s$ and $u_A=16\;m/s$, while the mole fraction of nitrogen diluents gas was varied from 0.0 to 0.2 with 0.1 step. For the analysis of flame structure and the flame stabilization mechanism, the simultaneous measurement of PIV/OH PLIF laser diagnostics had been performed. The stabilization point was selected in the most upstream region of the flame base and defined as the point where the turbulent flame propagation velocity was equal to the axial component of local flow velocity. We found that the turbulent flame propagation velocity increased with the decrease of nitrogen mole fraction. We concluded that the turbulent flame propagation velocity was expressed as a function of turbulent intensity and axial strain rate, even though nitrogen diluents mole fraction was changed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.3
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• pp.1028-1039
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• 1996

This study was focused on the examination of the flame structure and the combustion characteristics of diffusion flame which was formed the turbulent shear flow of a double coaxial air jet system. The shear flow was formed by the difference velocity of surrounding air jet(U$\_$s/) and center air jet (U$\_$c/). So experimental condition was divided S-type flame (.lambda. > 1) and C-type flame (.lambda. < 1) by velocity ratio .lambda. (=U$\_$s//U$\_$c/). For examination of the flame structure and the combustion characteristics in diffusion flame, coherent structure was observed in flame by schlieren photograph method. We measured fluctuating temperature and ion current simultaneously and accomplished the statistical analysis of its. According to schlieren photograph, the flame was stabilized in the rim of the direction of lower velocity air jet, coherent eddy was produced and developed by higher velocity air jet. The statistical data of fluctuating temperature and ion current was indicated that reaction was dominated by higher velocity air jet. The mixing state of burnt gas and non-burnt gas was distributed the wide area at Z = 100 mm of C-type flame.

• 한국연소학회:학술대회논문집
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• 2002.06a
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• pp.99-105
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• 2002

The concentration gradient effects on triple flame have been studied experimentally using a slot burner in order to stabilize stationary triple flame in coflowing stream. By means of contraction we generate the coflowing stream with uniform velocity and linear concentration gradient at the outlet of the slot. In this paper we investigated the response of the triple flame. to the concentration gradient, like the stability, the liftoff height, and the structure of triple flame. Flow velocity is measured with Laser Doppler Velocimetry. As the concentration gradient increases. the flame propagation velocity in immediately upstream triple point increases until the liftoff height of triple flame becomes minimum, and then decreases.

• 한국연소학회:학술대회논문집
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• 1998.10a
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• pp.91-101
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• 1998

The effect of secondary flow on both methane/air and propane/air premixed flame was investigated experimentally. By changing the radius of curvature, various flame behavior was observed. In the V-bend nozzles, flame surface is deformed from axisymmetry. As the exit velocity increased, flame lifted off partially. When the radius of curvature of the V-bend increased, the region where premixed flame is entirely on the rim increased. Since the axial velocity field is changed due to the secondary flow effect, comparison of V-bend and straight tube with the same diameter shows larger V-bend nozzle exit velocity for both flash back and flame blowout. The flame characteristics are mapped with a equivalence ratio, a velocity, and a nozzle radius of curvature. To identify physical reasoning on the flame surface deformation, numerical calculations are conducted. OH radical distributions in flames are visualized by PLIF technique.

• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.247-253
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• 2003

Burning velocities of conventional methane flame and oxygen-enriched methane flame were determined by experimentally and numerically at atmospheric pressure in order to examine the validity of various detailed reaction mechanisms in oxygen-enriched flame. The schlieren system was adopted to obtain the burning velocity of flame stabilized on a circular nozzle. Premix code was employed to compute the burning velocity. Three reaction mechnisms were tested at several oxygen enrichment level, whose names are GRI 3.0, MB(Miller and Bowman) and LKY(Lee Ki Yong) reaction mechanism. Sensitivity analysis was also performed to discriminate dominantly affecting reaction on burning velociy. The results showed that conventional reaction mechanisms originally based on methane-air flame were underpredict the burning velocity at high oxygen-enrichment level. The modified GRI 3.0 reaction mechanism based on our experimental results was suggested and shows a good agreement in estimating the burning velocity and the NO number density of oxygen-enriched flame.

• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.75-76
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• 2015

Lifted flame stabilization mechanism can be explained with constant Schmidt number from the equation of $H^{\ast}_L/d^2_o=const{\times}v_e^{(2Sc-1)/(Sc-1)}$. In this research, a method of local Schmidt number was applied in order to measure edge flame propagation velocities, and edge flame propagation velocity was calculated from the trend between lift-off height and nozzle flow rate.