• 한국연소학회:학술대회논문집
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• 한국연소학회 1998년도 제17회 KOSCI SYMPOSIUM 논문집
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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.

• Journal of Advanced Marine Engineering and Technology
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• 제33권2호
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• pp.259-266
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• 2009

An experimental study was conducted to investigate the effects of forcing amplitude on the flow structure near the nozzle exit of forced jet diffusion flames. The jet was excited up to the blowout occurrence by a considerable large amplitude with a periodic velocity fluctuation at the tube resonating frequency. In the attached flame regime, we disclosed the very interesting result newly that adding of a moderate forcing amplitude caused the jet flame to become longer in spite of being forced. Particular attention is focused on the turnabout mechanism of vortex roll-up around the elongated flame, which has not been reported previously, and on the inner coherent structure of the forced jet in the attached flame regime. From the velocity and flow visualization results, it was ascertained that the surrounding air due to the occurrence of negative velocity parts was suck into the fuel nozzle. To aid in understanding the rotating phenomenon of coherent structure, we present a schematic diagram of the turnabout mechanism of vortex roll-up. The mechanism of vortex turnabout phenomenon can be easily understood by considering the positive and negative velocity amplitudes about the instantaneous velocity of the forcing flow, as shown in this diagram.

• 한국연소학회지
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• 제17권1호
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• pp.22-29
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• 2012

The detachment stability characteristics of syngas $H_2$/CO jet attached flames were studied. The flame stability was observed while varying the syngas fuel composition, coaxial nozzle diameter and fuel nozzle rim thickness. The detachment stability limit of the syngas single jet flame was found to decrease with increasing mole fraction of carbon monoxide in the fuel. In hydrogen jet flames with coaxial air, the flame detachment stability was found to be independent of the coaxial nozzle diameter. However, velocities of appearance of liftoff and blowout velocities of lifted flames have dependence. At lower fuel velocity range, the critical coaxial air velocity leading to flame detachment increases with increasing fuel jet velocity, whereas at higher fuel velocity range, it decreases. This increasing-decreasing non-monotonic trend appears for all $H_2$/CO syngas compositions (50/50~100/0% $H_2$/CO). To qualitatively understand the flame behavior near the nozzle rim, $OH^*$ chemiluminescence imaging was performed near the detachment limit conditions. For all fuel compositions, local extinction on the rim is observed at lower fuel velocities(increasing stability region), while local flame extinction downstream of the rim is observed at higher fuel velocities(decreasing stability region). Maximum values of the non-monotonic trends appear to be identical when the fuel jet velocity is normalized by the critical fuel velocity obtained in the single jet cases.

• 한국연소학회지
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• 제16권1호
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• pp.15-21
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• 2011

An experimental study was conducted to investigate the flame stability of the synthetic gas (syngas) using an impinging premixed jet burner. Since the syngas mainly consisted of $H_2$ and CO, the $H_2$/CO mixture was simulated as the syngas. $H_2$/CO mixture ratios, fuel/air mixture velocities and equivalence ratios were used as major parameters on the flame stabilitym The role of the impinging plate on the flame stability was also examined. In addition, laminar burning velocities of the $H_2$/CO mixture were predicted numerically to understand the characteristics of the flame stability for the syngas. The increase in the H2 concentration into the syngas brings about the extension of the blowout limit and the reduction in the flashback limit in terms of the stable flame region. The impinging jet plate broadened the blowout limit but does not play important role in changing of the flashback limit. Finally, it was found that the stability region of the flame using the syngas, which is expressed in terms of the mixture velocity and the equivalence ratio in this study, significantly differed from that of $CH_4$.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.888-890
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• 2002

We derived a theory of increasing electromagnetic force acting on arc column for reducing arcing time between electric contacts. A simulation method of arc velocity is presented by calculating blowout force using 3D FEM and drag acting on arc column. This paper is proposed 3 types arc extinguish chamber of different fulx path and is presented electromagnetic force and arc velocity of each model.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1365-1370
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• 2004

It has been reported that if eight small nozzles are arranged along the circle of 40 $^{\sim}$ 72 times the diameter of single nozzle, the propane non-premixed flames are not extinguished even in 200m/s, In this research, experiments were extended to the methane flame. Nine nozzles were used- eight was evenly located along the perimeter of the imaginary circle and one at the geometric center. The space between nozzles, s, the exit velocity and the role of the jet from the center nozzle were considered. On the contrary to the propane non-premixed case, the maximum blowout velocity for the methane diffusion flame was achieved when small amount of fuel is supplied through the center nozzle and s/d equals around 21. In the laminar region, the flame attached at the center nozzle anchored the outer lifted flames.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
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• pp.165-172
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• 1999

Landfill gas has merely half heating value compared with liquified natural gas but can be greatly utilized as a commercial fuel. The authors have examined emission characteristics as well as measured burning velocity of LFG mixed gas which contains plenty of $CO_{2}$. With the viewpoint of fuel utilization, flame stability could be one of important characteristics of LFG. In this study, the comparison experiments are conducted between $CH_{4}$ and LFG for searching the region of flame stabilization based upon the flame blowout at maximum fuel stream velocity. As a result, it is found that stabilization region of LFG is not improved with that of $CH_{4}$ in non-swirl/or weak swirl jet diffusion flame. However, it is also known that flame stability is hardly affected by inert gas in the strong swirl with considering widened flame stabilization region of LFG rather than LNG.

• 한국연소학회:학술대회논문집
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• 대한연소학회 2003년도 제27회 KOSCO SYMPOSIUM 논문집
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• pp.177-184
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• 2003

Stabilization mechanism of lifted flame in the near field of coflow jets has been investigated experimentally and numerically for methane fuel diluted with nitrogen. Lifted flames were observed only in the near field of coflow jets until blowout occurred in the normal gravity condition. To elucidate the stabilization mechanism for the stationary lifted flames in the near field of coflow jets for the diluted methane having the Schmidt number smaller than unity, the behaviors of the stationary lifted flame in microgravity and unsteady propagation phenomena were investigated numerically at various conditions of jet velocity. It has been founded that the buoyancy plays an important role for flame stabilization of lifted flame in normal gravity and the stabilization mechanism is due to the significant variation of the propagation speed of lifted flame edge compared to the local flow velocity at the edge.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제55권3호
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• pp.146-154
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• 2006

We derived a theory of increasing electromagnetic force which acts on arc column for reducing arcing time between electric contacts. A simulation method of arc velocity is presented by calculating blowout force using 3D FEM and drag force acting on arc column. This paper proposes 3 types arc extinguish chamber of different flux path and presents the specific electromagnetic force and arc velocity of each model by the analysis. The result of analysis and experimental proposes the prediction method of arc time when all conditions are same except external magnetic field.

• 한국연소학회지
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• 제21권2호
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• pp.22-28
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• 2016

High efficient and environment friendly combustion technologies are used to be operated an extreme condition, which results in unintended flame instability such as extinction and oscillation. The use of electromagnetic energy is one of methods to enhance the combustion stability and a microwave as electromagnetic wave is receiving increased attention recently because of its high performance and low-cost system. In this study, an experiment was performed with jet diffusion flames induced by microwave. Micro jet was introduced to simulate the high velocity of industrial combustor. The results show that micro jet flames had three different modes with increasing oxidizer velocity; attached yellow flame, lifted flame, and lifted partially premixed flame. As a microwave was induced to flames, the overall flame stability and blowout limit were extended with the higher microwave power. Especially the interaction between a flame and a microwave was shown clearly in the partially premixed flame, in which the lift-off height decreased and NOx emission measured in post flame region increased with increasing microwave power. It might be attributed to increase of reactivity due to the abundance of radical pool and the enhanced absorption to thermal energy.