• 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.

• 대한기계학회논문집B
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• 제29권3호
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• pp.349-355
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• 2005

It has been reported that propane non-premixed interacting flames are not extinguished even in 210m/s if eight small nozzles are arranged along the imaginary circle of 40 ~ 72 times the diameter of single nozzle. 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 flame, small amount of fuel fed through the center nozzle makes the methane diffusion flame stable even at the choking conditions. In the laminar region, the flame at the center nozzle anchored the outer lifted flames.

• 대한기계학회논문집B
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• 제27권9호
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• pp.1209-1219
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• 2003

The dynamic behaviors of the single vortex interacting with $CH_4-Air$ jet diffusion flame are investigated numerically. The numerical method is based on a predict-corrector scheme for a low Mach number flow. A two-step global reaction mechanism is adopted as a combustion model. Studies are conducted in fixed initial velocities for the three cases according as where $CO_2$ is added; (1) without dilution, (2) dilution in fuel stream and (3) dilution in oxidizer stream. A single vortex is generated by an axisymmetric jet, which is made by an impulse of a cold fuel when a flame is developed entirely in a computational domain. The simulation shows that $CO_2$ dilution in fuel stream results in somewhat larger vortex radius, and greater amount of entrainment of surrounding fluid than in other cases. Thus, the dilution of $CO_2$ in fuel stream enhances the mixing in single vortex and increases the stretching of the flame surface. The budgets of the vorticity transport equation are examined to reveal the mechanism of vortex formation when $CO_2$ is added. It is found that, in the case of $CO_2$ dilution in fuel stream, the vortex destruction due to volumetric expansion and the vortex production due to baroclinic torque are more dominant than in other cases.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2000년도 제21회 KOSCO SYMPOSIUM 논문집
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• pp.47-58
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• 2000

The relationship among the flame radiation, NOx emissions, residence time, and global strain rate are examined for turbulent non-premixed jet flames with wide variations in coaxial air conditions. Measurements of NOx emission, flame geometry and flame radiation were made to explain the NOx emission scaling based on global parameters such as flame residence time, global strain rate, and radiant fraction. The overall 1/2-power scaling is observed in coaxial air flames, irrespective of coaxial air conditions, but the degree of deviation from the l/2-slope curve in each case differs from one another. From the comparison between the results of pure hydrogen flames and those of helium diluted hydrogen flames, it is observed that flame radiation plays a significant role in pure hydrogen flames with coaxial air and the deviation from 1/2-power scaling may be explained in two reasons: the difference in the flame radiation and the difference in jet similarity in coaxial air flames. From the radiation measurements, more detailed explanations on these deviations were suggested.

• 한국화재소방학회논문지
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• 제23권1호
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• pp.55-62
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• 2009

층류영역의 분출유량에서 큰 가진강도 효과를 얻기 위해 연료관 관 공명주파수로 가진된 비예혼합 분류 화염의 일반적인 가진 연소특성을 실험적으로 조사하였다. 화염 안정화 특성에서는 두 가지 형태의 부상 특성이 존재하는 사실을 알았는데, 화염이 부상되는 가진강도 크기에서 한 쪽은 감소, 다른 영역에서는 증가하는 것으로 나타나 각각 서로 다른 부상기구가 존재함을 확인할 수 있었다. 특히 부상되지 않고 노즐에 부착된 분출유량 영역에서의 가진 연소특성을 가진 강도에 따른 화염 길이와 형상, 유동장 응답 특성 그리고 노즐 출구에서의 유속 분포를 중심으로 집중 조사하였다. 특이한 현상으로는 가진 강도 증가에 따라 화염의 신장과 in-burning 현상 그리고 화염 내 거동 와동들의 말림방향이 서로 역전되는 현상 등이 발견되었다. 노즐 출구의 유속분포와 가시화 기법을 통해 이러한 현상들이 노즐관 관벽 안쪽서부터 음의 속도가 발생하기 시작함에 따라 주변 산화제인 공기가 노즐관 안으로 유입되는 현상과 관련되는 것으로 파악되었다.

• 대한기계학회논문집
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• 제14권5호
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• pp.1234-1243
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• 1990

본 연구에서는 선회가 없는 중심기류와 주위기류의 난류 전단층에서 형성되는 난류확산화염의 천이영역(transition region)에 주목하여 전단층내의 혼합작용과 화염 구조와의 상호작용을 규명하기 위해 거시적 및 순간적인 화염구조에 대해 실험적으로 조사 연구한 결과를 보고한다.

• 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.

• 한국연소학회지
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• 제15권4호
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• pp.15-21
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• 2010

The transported probability density function(PDF) model has been applied to simulate the turbulent nonpremixed piloted jet flame. To realistically account for the mixture fraction PDF informations on the turbulent non-premixed jet flame, the present Lagrangian PDF transport approach is based on the joint velocity-composition-turbulence frequency PDF formulation. The fluctuating velocity of stochastic fields is modeled by simplified Langevin model(SLM), turbulence frequency of stochastic fields is modeled by Jayesh-Pope model and effects of molecular diffusion are represented by the interaction by exchange with the mean (IEM) mixing model. To validate the present approach, the numerical results obtained by the joint velocity-composition-turbulence frequency PDF model are compared with experimental data in terms of the unconditional and conditional means of mixture fraction, temperature and species and PDFs.

• 한국연소학회지
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• 제7권3호
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• pp.9-15
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• 2002

Soot generation by combustion process has been investigated with objective of understanding of chemical reaction responsible for its formation in a coaxial laminar propane jet diffusion flame. For the direct photos, as the coflowing air flow rate is reduced, the area of soot luminous zone increases at first, then becomes smaller and smaller, and even disappears. The aspects of soot deposition can be acquired by using nine $15{\mu}m$ thin SiC fibers are positioned horizontally across the flame. Deposited soots on SiC fibers show the soot inception point and growth and soot oxidation zone in a typical propane diffusion. Soot is not generated anymore in a oxidizer deficient conditions of near-extinction and flame is fully occupied by transparent blue flame. It suggests that nonsooting pyroligneous blue reaction is being dominant in a oxidizer deficient ambience. In comparison with luminosities of SiC fibers and flame itself, indirect evidence is found that the process of soot nucleation and growth is endothermic reaction. It is remarkable that there exists two adjacent regions to have antithesis characteristics; one is exothermic reaction of blue flame and another endothermic reaction zone of soot formation.

• 한국안전학회지
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• 제31권3호
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• pp.22-27
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• 2016

The use of electromagnetic wave has been interested in various energy industry because it enhances a flame stability and provides higher safety environments. However it might increase the pollutant emissions such as NOx and soot, and have harmful influence on human and environments. Therefore, it is very important to understand interaction mechanism between flame and electromagnetic wave from environmental point of view. In this study, an experiment was performed with jet diffusion flames induced by electromagnetic wave. Microwave was used as representative electromagnetic wave and a flickering flame was introduced to simulate the more similar combustion condition to industry. The results show that the induced microwave enhances the flame stability and blowout limit. The unstable lifted flickering flames under low fuel/oxidizer velocity is changed to stable attached flames or lift-off flames when microwave applied to the flames, which results from the abundance of radical pool. However, NOx emission was increased monotonically with increasing the microwave power as microwave power increased up to 1.0 kW. The effects might be attributed to the heating of combustion field and thermal NOx mechanism will be prevailed. Soot particle was examined at the post flame region by TEM grid. The morphology of soot particle sampled in the microwave induced flames was similar to the incipient soot that is not agglomerated and contain a lots of liquid phase hydrocarbon such as PAH, which soot particle formed near reaction zone is oxidized on the extended yellow flame region and hence only unburned young particles are emitted on the post flame region.