• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.85-91
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• 2003

The lift-off characteristics of the triple flame within a diverging duct have been studied experimentally using a multi-slot burner, which can control the concentration gradient and the mean velocity independently. In this experiment the triple flame was stabilized successfully in lift-off condition and flame stabilization with a duct or without a duct, lift-off heights, and some other characteristics were examined for propane flame. It was examined that the effects with various concentration gradient and mean velocity on the triple flame. It was found that minimum value of the lift-off heights exist at a certain concentration gradient for constant mean velocity and flame with a duct is more stable than that without. Moreover the propagation velocity of the flame becomes maximum at a certain concentration gradient regardless of mean velocity.

• 한국연소학회:학술대회논문집
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• 2001.11a
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• pp.97-103
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• 2001

The characteristics of flame stability have been studied experimentally using a slot burner. The blowout conditions of a fuel-lean premixed laminar flame, which is located in the middle of fuel-rich premixed laminar flames, are identified for propane, ethylene, and methane flames. The fuel-rich flames could stabilize the fuel-lean flame for the equivalence ratio as low as 0.2. The laminar flame speed along with the heat release rate is likely to be the important factor in stabilizing a fuel-lean flame. The increase of heat release rate on a fuel-rich flame lowers the equivalence ratio limit for the stable fuel-lean flames. The stability of fuel-lean flames, however, was not sensitive to the equivalence ratio of a fuel-rich flame.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.2
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• pp.211-216
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• 2012

The availability of thermal energy has been widely recognized recently, and the cascade usage of thermal energy from combustion has been encouraged. Within this framework, a 1-kW-class Stirling-engine.based cogeneration system has been proposed as a unit of a distributed energy system. The capacity has been designed to be adequate for domestic usage, which requires high compactness as well as low emissions and noise. To develop a highly efficient system satisfying these requirements, a premixed slot-type short-flame burner has been proposed, and a series of experiments has been performed to understand its combustion characteristics. Flame images have been captured to observe the dependence of the flame mode on the combustion load and air/fuel ratio. The exhaust gas has been sampled and analyzed to study the emission characteristics for each flame mode.

• 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.

• 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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• 2004.11a
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• pp.85-90
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• 2004

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 is decreased to the minimum value and then increase 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. 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. 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.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.60-64
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• 2006

Propagation rates ($U_{edge}$) of various premixed, twin edge-flames were measured as a function of global strain rate ($\sigma$), mixture strength, and Lewis number (Le). Using a counterflow slot-jet burner with electrical heaters at each end, both advancing (positive $U_{edge}$) and retreating (negative $U_{edge}$) edge-flames can be studied as they propagate along the long dimension of the burner. Experimental results are presented for premixed methane/air twin flames in terms of the effects of $\sigma$ on $U_{edge}$. Both low-$\sigma$ and high-$\sigma$ extinction limits were discovered for all mixtures tested. As a result, the domain of edge-flame stability was obtained in terms of heat loss factor and normalized flame thickness, and comparison with the numerical result of other researchers was also made. For low ($CH_4/O_2/CO_2$) and high ($C_3H_8$/air) Lewis number cases, propagation rates clearly show a strong dependence on Le.

• 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 the Korean Society of Combustion
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• v.14 no.1
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• pp.25-30
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• 2009

Propagation rates ($U_{edge}$) of various premixed, twin edge-flames were measured as a function of global strain rate ($\sigma$), mixture strength, and Lewis number (Le). Using a counterflow slot-jet burner with electrical heaters at each end, both advancing (positive $U_{edge}$) and retreating (negative $U_{edge}$) edge-flames can be studied as they propagate along the long dimension of the burner. Experimental results are presented for premixed methane/air twin flames in terms of the effects of $\sigma$ on $U_{edge}$. Both low-$\sigma$ and high-$\sigma$ extinction limits were discovered for all mixtures tested. As a result, the domain of edge-flame stability was obtained in terms of heat loss factor and normalized flame thickness, and comparison with the numerical result of other researchers was also made. For low ($CH_4/O_2/CO_2$) and high ($C_{3}H_{8}$/air) Lewis number cases, propagation rates clearly show a strong dependence on Le.