• Journal of Advanced Marine Engineering and Technology
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• 제30권8호
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• pp.853-862
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• 2006

The present study is numerically investigated the flame structure of non-premixed counterflow jet flames using the laminar flamelet model Detailed flame structures with the fuel composition of 40% CO, 30% $H_2$. 30% $N_2$ and an oxidizer composition of 79% $N_2$ and 21% $O_2$ in a non-premixed counterflow flame are studied numerically. This study is aimed to investigate the effects of axial velocity gradient and combustion atmosphere pressure on flame structure. The results show that the role of axial velocity gradient on combustion processes is globally opposite to that of combustion atmosphere pressure. That is, chemical nonequilibrium effects become dominant with increasing axial velocity gradient, but are suppressed with increasing ambient pressure. Also, the flame strength is globally weakened by the increase of axial velocity gradient but is augmented by the increase of ambient pressure. However, flame extinction is described better on the basis of only chemical reaction and in this study axial velocity gradient and ambient pressure play a similar role conceptually such that the increase of axial velocity gradient and ambient pressure cause flame not to be extinguished and extend the extinction limit, respectively. Consequently it is suggested that a combustion process like flame extinction is mainly influenced by the competition between the radical formation reaction and the third-body recombination reaction.

• 대한조선학회논문집
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• 제33권3호
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• pp.94-102
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• 1996

유한변형문제에서 변형구배텐서를 탄소성 성분으로 분해하기 위한 가산분해와 곱분해방법에 대해서 설명하고, 이 두 방법에서 파생되는 역학량들의 의미와 그 차이점을 보였다. 변형구배에 대한 기존의 곱분해와 가산분해로 얻어지는 변형속도구배는 가산적으로 표현되지 않으며, 소성변형속도구배는 탄성변형의 영향을 받고 있다. 본 연구에서는 공축소성 가정을 도입하고, 수정된 곱분해를 통하여 소성변형속도구배가 탄성변형에 영향을 받지 않는 가산적인 변형속도 구배를 얻었다.

• 한국안전학회지
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• 제21권5호
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• pp.1-5
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• 2006

This study provides a basic data necessary to design a facility of smoke management after calculating the critical velocity of the gradient scale model tunnel and reviewing its adequacy to establish an optimum disaster prevention system for a road tunnel at fire. The experiment is carried out by using Froude scaling to a scale model which is about 1/29 as big as the real tunnel, and its critical velocity calculation is calculated to the 0-2% gradient of the tunnel. The result shows that the higher the gradient is, the stronger the critical velocity, but that it doesn't affect the critical velocity so much when the gradient is less 2%. In addition, this result is studied in comparison with the results done by other researchers to review the adequacy of the critical velocity.

• 한국연소학회:학술대회논문집
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• 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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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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• 한국연소학회 2004년도 제28회 KOSCO SYMPOSIUM 논문집
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• pp.7-14
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• 2004

The lift-off characteristics of the triple flame have been studied experimentally with various mean velocities and concentration gradients using a multi-slot burner, which can control the concentration gradient and the mean velocity independently, Lift-off height, axial maximum velocity, flame temperature, and some other characteristics were examined for methane and propane flame, It was found that minimum values of the lift-off heights exist at a certain concentration gradient for constant mean velocity, and this result implies that the propagation velocity has a maximum value at this condition, OH radical distribution was measured with LIF method and velocity variation along streamline was measured with PlV system. In addition maximum temperature along streamline was measured with CARS system. The intensity of the diffusion flame affects on the propagation velocity of triple flame in the region of very weak concentration gradient.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2002년도 제24회 KOSCO SYMPOSIUM 논문집
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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.

• Journal of Mechanical Science and Technology
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• 제19권4호
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• pp.1027-1035
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• 2005

Thermophoresis in dense gases is studied by using a multi-scale approach and Born- Yvon­Green (BYG) equation. The problem of a particle movement in an ambient dense gas under temperature gradient is divided into inter and outer ones. The pressure gradient in the inner region is obtained from the solutions of BYG equation. The velocity profile is derived from the conservation equations and calculated using the pressure gradient, which provides the particle velocity in the outer problem. It is shown that the temperature gradient applied to the quiescent ambient gas induces some pressure gradient and thus flow tangential to the particle surface in the interfacial region. The mechanism that induces the flow may be the dominant source of the thermophretic particle movement in dense gases. It is also shown that the particle velocity has a nonlinear relationship with the applied temperature gradient and decreases with increasing temperature.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2001년도 추계학술대회 논문집(Proceeding of the KOSME 2001 Autumn Annual Meeting)
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• pp.36-44
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• 2001

The effects of various tripping structures on turbulent boundary layer subjected to adverse pressure gradient were examined. The profiles are compared to zero pressure gradient and adverse pressure gradient. The increases of tripping structures of height, k are affects almost flow parameter included velocity fluctuation, skin friction coefficient and turbulent boundary thickness.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2005년도 제31회 KOSCO SYMPOSIUM 논문집
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• pp.221-228
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• 2005

The tribrachial flame in laminar coflow jet has been investigated experimentally with unsteady propagating condition. In this experiment, we found that the tribrachial point has an angle of flame surface because the location of tribrachial point is not on the base point of flame but on the inclined surface of flame. This angle of Flame surface at tribrachial point are increasing when the flame is approaching to the nozzle exit. With considering this angle of flame surface, the radial velocity gradient can affect flame propagation speed by increasing flow-stretch effect. The propagation speed of tribrachial flame was calculated with including above stretch effect. The speed decreases with increasing velocity gradient due to the increment of stretch effect.

• 대한기계학회논문집B
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• 제27권8호
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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.