• 대한기계학회논문집B
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• 제28권2호
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• pp.160-166
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• 2004

Combustion using oxygen enriched air is known as a technology which can increase flame stability as well as thermal efficiency due to improving the burning rate. Lift-off, blowout limit and flame length were examined as a function of jet velocity, coflow velocity and OEC(Oxygen Enriched Concentration). Blowout limit of the flame below OEC 25% decreased with increase of coflow velocity, but the limit above OEC 25% increased inversely. Lift-off height decreased with increase of OEC. In particular, lift-off hardly occurred in the condition above OEC 40%. Flame length of the flames above OEC 40% was increased until the blowout occurred. Great flame stability was obtained since lift-off and blowout limit significantly increased with increase of OEC.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.326-331
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• 2003

Combustion using oxygen enriched air is known as a technology which can increase flame stability as well as thermal efficiency due to improvement of the burning rate. Lift-off, blowout limit and flame length were examined as a function of jet velocity, coflow velocity and OEC(Oxygen Enriched Concentration). Blowout limit of the flame below OEC 25% decreased with coflow velocity, but the limit above OEC 25% increased inversely. Lift-off height decreased with increase of OEC. Especially lift-off hardly occurred in the condition above OEC 40%. Flame length of the flames above OEC 40% was increased until the blowout occurred. Flame stability became improved since lift-off and blowout limit increased much with increase of OEC.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2003년도 추계학술대회 논문집
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• pp.107-110
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• 2003

Characteristics of PAH and soot formation in coflow diffusion flames of methane, methane, propane, and ethylene have been experimentally studied to investigate the temperature and fuel structure effect on soot formation. PAH and soot images were acquired by applying PAH LIF and LII techniques, respectively and temperature was measured using R-type thermocouple. Direct photographs of soot particles have also been taken by transmission electron microscopy (TEM) through a thermophoretic sampling. Comparison of PAH and soot formation between the aliphatic fuels has shown the importance of fuel structure effect in diffusion flames.

• 한국연소학회지
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• 제10권1호
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• pp.13-19
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• 2005

Measurements of flame length and NOx emissions have been conducted to investigate the effects of acoustic excitation on flame structure in turbulent hydrogen diffusion flames with coaxial air. When the acoustic excitation of a specific frequency is applied to coaxial air stream, flame length is dramatically reduced, resulting in reduction of flame residence time. Consequently, EINOx could decrease up to 35 % and this shows that acoustic excitation is effective in reducing NOx emissions. Mie scattering technique has been used to visualize the vortex structure induced by acoustic excitation and vortex formation, development and destruction were observed quantitatively. As a result, vortex entrains coflow air into fuel stream and mixing rate between fuel and air is significantly enhanced, which may contribute to reduction of NOx emissions.

• Journal of Advanced Marine Engineering and Technology
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• 제40권2호
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• pp.102-106
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• 2016

An experimental study on the flow characteristics under various laminar coflow diffusion flames was conducted with a particular focus on the buoyancy force exerted from gaseous hydrocarbon fuels. Methane ($CH_4$), ethylene ($C_2H_4$), and n-butane ($C_4H_{10}$) were used as the fuels. A coflow burner and the Schlieren imaging technique were used to observe the flow field of each fuel near the nozzle exit as well as the flow characteristics in the flames. The results show that a vortex with a density heavier than air appeared in n-butane near the nozzle exit with a strong negative buoyancy on the fuel steam. As the Reynolds number increased through the control of the fuel velocity of the n-butane flame, the vortices were greater and the vortex tips were moved up from the nozzle exit. In addition, the heated nozzle affected the flow fields of the fuel steam near the nozzle exit.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2001년도 제23회 KOSCO SYMPOSIUM 논문집
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• pp.119-124
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• 2001

Propane coflow diffusion flames have been experimentally studied to investigate the liftoff and reattachment characteristics. Flame properties such as velocity and density distribution were measured by LDV and shadowgraphy, respectively. It is shown that as the velocity of coflowing air increases, liftoff velocity decreases nonlinearly in turbulent jets and linearly in laminar jets, while reattachment velocity decreases nonlinearly. Meanwhile, as inner nozzle tip thickness increases, liftoff velocity increases with the reattachment velocity nearly unchanged. Liftoff phenomena in these flames can be categorized into three classes as a function of coflow velocity, such as laminar liftoff, turbulent liftoff, and transient liftoff.

• 대한기계학회논문집B
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• 제36권6호
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• pp.639-646
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• 2012

가열된 동축류 공기에서 일산화탄소/수소의 층류 제트에 대한 자발화된 부상화염의 특성을 조사하였다. 그 결과로 자발화가 발생하지 않는 영역에서는 제트속도의 증가에 따라 노즐부착화염에서 안정화된 층류 부상화염을 거치지 않고 바로 화염날림이 발생하였다. 자발화 영역에서, 질소 희석된 일산화탄소의 자발화된 부상화염은 산화제 내의 함유된 수분에 따른 점화지연시간의 변동으로 그 부상높이가 크게 영향을 받았다. 그리고 수소에 의한 저온 자발화 영역에서 자발화된 부상화염은 제트속도의 증가에 따라 부상높이가 감소하다가 증가하는 독특한 현상이 발생하였다. 점화지연시간에 의한 자발화된 층류 부상화염의 안정화 메커니즘을 기반으로, 그 부상높이의 거동은 점화 과정에서 발생하는 열손실의 영향뿐만 아니라 연료제트의 운동량과 질량의 선호 확산에 의하여 영향을 받을 수 있다는 것을 확인하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1347-1352
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• 2004

In this work, $TiO_{2}$ nanoparticles were synthesized using a $N_{2}-diluted$ hydrogen coflow diffusion flame. The effect of flame temperature on the crystalline structure and the size of formed nanoparticles was investigated. The maximum centerline temperature of the flame ranged from 1,920K for $H_{2}-only$ flame to 863K for 81% $N_{2}-diluted$ flame. When the temperature was higher than about 1,000K, the particle size was tend to increase due to the agglomeration and sintering among the primary particles. On the other hand, when the temperature was lower than 1,000K, the portion of anatase phase was greater than 80%.

• 한국연소학회지
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• 제11권1호
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• pp.11-18
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• 2006

In this work, $TiO_2$ nanoparticles were synthesized using $N_2-diluted$ and Oxygen-enriched coflow hydrogen diffusion flames. The effect of flame temperature on the characteristics of the formed $TiO_2$ nanoparticles was investigated. The measured maximum centerline temperature of the flame ranged from 2,103 K for oxygen-enriched flame to 1,339 K for $N_2-diluted$ flame. The visible flame length and the height of the main reaction zone were characterized by direct photographs. The characteristics of synthesized $TiO_2$ nanoparticles were analyzed by SEM and TEM images. From these images, it was evident that the formed nanoparticles were divided into two sorts. In the higher temperature region, over the 1,700 K, $TiO_2$ nanoparticles having spherical shapes with diameters about 60 nm were synthesized. In the lower temperature region, below the 1,600 K, the diameters of formed nanoparticles having unclear boundaries were ranged from 35 - 50 nm.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
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• pp.167-170
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• 2012

Self-excitations of edge flame were studied in laminar lifted free- and coflow-jet as well as counterflow flames diluted with nitrogen and helium. The self-excitations, originated from variation of edge flame speed and found in the above-mentioned configurations, are discussed. A newly found self-excitation and flame blowout, caused by the conductive heat loss from premixed wings to trailing diffusion flame are described and characterized in laminar lifted jet flames. Some trials to distinguish Lewis-number-induced self-excitation from buoyancy-driven one with O(1.0 Hz) are introduced, and then the differences are discussed. In counterflow configuration, important role of the outermost edge flame in flame extinction is also suggested and discussed.