• 한국항공우주학회지
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• 제42권12호
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• pp.1004-1012
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• 2014

본 연구에서는 보염기가 장착된 덕트형 연소기에 음향 가진을 주었을 때 화염의 날림 현상을 이해하기 위한 실험을 수행하였다. 화염 구조를 관측하기 위한 촬영기법으로는 $OH^*$ 자발광이 적용되었고 POD (Proper Orthogonal Decomposition) 알고리즘을 이용하여 이미지를 분석하였다. 연료는 메탄이 주 성분인 도시가스를 사용했으며 당량비를 낮춤으로써 화염 날림이 발생하도록 하였다. 공기 공급 유량, 가진 주파수 및 음압에 변화를 주며 실험을 하여 화염 날림이 발생하는 당량비를 측정하였다. 실험 조건에 따라 화염 날림 당량비 값이 크게 달랐으며 이러한 당량비 값에 변화를 주는 요인은 보염기 후류의 와류 주파수와 연소기 공진 효과의 영향으로 판단된다.

• 대한기계학회논문집B
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• 제26권1호
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• pp.133-140
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• 2002

This article presents an application of a large-scale structural mixing model(Broadwell et at. 1984) to the blowout of turbulent reacting cross flow jets. Experimental observations, therefore, aim to identify the existence of large-scale vortical structure exerting an important effect upon the flame stabilization. In the analysis of common stability curve, it is seen that the phenomenon of blowout are only related to the mixing time scale of the two flows. The most notable observation is that the blowout distance is traced at a fixed positions according to the velocity ratio at all times. Measurements of the lower blowout limits in the liftable flame are qualitatively in agreement with the blowout parameter $\xi$, proposed by Broadwell et al. Good agrement between the results calculated by a modified blowout parameter $\xi$'and the present experimental results confirms the important effect of large-scale structure in the stabilization feature of blowout.

• 대한기계학회논문집B
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• 제26권1호
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• pp.125-132
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• 2002

An experimental study on the characteristics of stability of propane turbulent nonpremixed jet flames discharged normal to air free-streams with uniform velocity profile is conducted. Experimental observations are focused on the flame shape, the stability considering two kinds of flame, lift-off distance, and the flame length according to velocity ratio. In order to investigate the mixing structure of the flame base at the lower limit, we employ the RMS technique and measure the species concentration by a gas chromatography. In the results of the stability curve and lifted flame, it is fecund that the dependency of nozzle diameter is closely related to the large-scale vortical structure representing counter-rotating vortices pair. Also, the detailed discussion on the phenomenon of blowout due to this large vortical motion, is provided.

• 대한기계학회논문집B
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• 제34권7호
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• pp.729-738
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• 2010

질소로 희석된 부탄 층류 부상 화염에서 발생할 수 있는 화염진동 메커니즘을 살펴보기 위하여 실험적 연구를 수행하였다. 화염 진동은 층류 자유제트 부상 화염에서 5가지 영역으로 구분되었다: 화염 안정화 영역 (I), 열손실에 의한 진동 (II), 열손실에 의한 진동과 부력에 의한 진동이 혼재된 영역 (III),열손실에 의한 진동과 화염날림 직전의 진동이 혼재된 영역 (IV), 그리고 열손실에 의한 진동, 부력에 의한 진동 및 화염날림 직전의 진동이 모두 혼재된 영역(V). 각각의 화염진동의 특성을 규명하기 위해 화염의 시간에 따른 부상 높이 변화에 대한 FFT분석을 수행하였고 각 영역에 관련된 무차원 변수와 스트라훌 수의 조합으로 특성화 작업을 수행하였다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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• pp.201-207
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• 2003

Characteristic of turbulent nonpremixed interacting flames are investigated experimentally 8 or 9 nozzles are arranged in the shape of matrix or circle. When there is no center nozzle, flame is more stable than with center nozzle case. It is shown that these blowout limit enlargements are related with the recirculation of burnt gases. The interacting flame base was not located at the stoichiometric point. NO concentrations of interacting flame are smaller than that of single flame using same area nozzle.

• 대한기계학회논문집B
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• 제29권1호
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• pp.71-79
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• 2005

For the non-premixed interacting jet flames, it has been reported that if eight small nozzles are arranged along the circle of $40{\sim}72$ times the diameter of single jet, the flames are not extinguished even in 200m/s. In this research, experiments were extended to the partially premixed cases to reduce both flame temperature and NOx emission. Nine nozzles were used- eight was evenly located along the perimeter of the imaginary circle and one at the geometric centre. The space between nozzles, S, the equivalence ratio, ${\phi}$, the exit velocity and the role of the jet from the centre nozzle were considered. Normally, flame was lifted and flame base was located inside the imaginary circle made by the nozzle. As nozzles went away from each other, blowout velocity increased and then decreased. The maximum blowout velocity diminished with the addition of air to the fuel stream. When the fuel and/or oxidizer were not fed through the centre nozzle, the maximum blowout velocity obtained by varying S and ${\phi}$ was around 160m/s. Optimum nozzle separation distance at which peak blowout velocity obtained also decreased with ${\phi}$ decrease. Flame base became leaner as approaching to the blowout. It seemed that lots of air was supplied to the flame stabilizing region by the entrainment and partially premixing. To approve this idea and to enhance the blowout velocity, fuel was supplied to the centre region. With the small amount of fuel through the centre nozzle, partially premixed flame could be sustained till sonic velocities. It seemed that the stabilizing mechanism in partially premixed interacting flame was different from that of non-premixed case because one was stabilized by the fuel supply through the centre nozzle but the other destabilized.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제29회 KOSCI SYMPOSIUM 논문집
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• pp.79-84
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• 2004

For the non-premixed interacting jet flames, it has been reported that if eight small nozzles are arranged along the circle of 40 $^{\sim}$ 72 times the diameter of single jet, the flames are not extinguished over 2oom/s. In this research, experiments were extended to the partially premixed cases to reduce both flame temperature and NOx emission. Nine nozzles were used- eight was evenly located along the perimeter of the imaginary circle and one at the geometric centre. The space between nozzles, S, the equivalence ratio, ${\Phi}$, the exit velocity and the role of the jet from the centre nozzle were considered. Normally, flame was lifted and flame base was located inside the imaginary circle made by the nozzle. As nozzles went away from each other, blowout velocity increased and then decreased. The maximum blowout velocity diminished with the addition of air to the fuel stream. When the fuel and/or oxidizer were not fed through the centre nozzle, the maximum blowout velocity obtained by varying Sand ${\Phi}$ was around 160m/s. Optimum nozzle separation distance at which peak blowout velocity obtained also decreased with ${\Phi}$ decrease. Flame base became leaner as approaching to the blowout. It seemed that lots of air was supplied to the flame stabilizing region by the entrainment and partially premixing. To approve this idea and to enhance the blowout velocity, fuel was supplied to the centre region. With the small amount of fuel through the centre nozzle, partially premixed flame could be sustained till sonic velocities. It seemed that the stabilizing mechanism in partially premixed interacting flame was different from that of non-premixed case because one was stabilized by the fuel supply through the centre nozzle but the other destabilized.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.453-458
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• 2001

The stability of turbulent nonpremixed interacting flames is investigated in terms of nozzle configuration shapes which depend on the existence of the center nozzles. Six nozzle arrangements which are cross 4, 5, 8, 9, square 8 and circular 8 nozzles are used for the experiment. Those are arranged to see the effect of the center nozzle out of multi-nozzle. There are many parameters that affect flame stability in multi-nozzle flame such as nozzle separation distance, fuel flowrates and nozzle configuration, but the most important factor is the existence of nozzles in the center area from the nozzle arrangement. As the number of nozzle in the area is reduced, more air can be entrained into the center of flame base and then tag flame is formed. In the case of circular 8 nozzles, blowout flowrates are above 5.4 times compared with that of single equivalent area nozzle.

• 대한기계학회논문집B
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• 제27권10호
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• pp.1420-1426
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• 2003

The stability of turbulent nonpremixed interacting flames is investigated in terms of nozzle configuration shapes and kind of fuels. Four nozzle arrangements - cross 5, matrix 8, matrix 9 and circle 8 nozzles - are used in the experiment. There are many parameters affecting flame stability in multi-nozzle flames such as nozzle separation distance, fuel flowrates and nozzle configuration etc. Key factors to enhance blowout limit are the nozzle configuration and the existence of center nozzle. Even nozzle exit velocity equal 204 m/s, flame is not extinguished when there is not a center nozzle and s/d=15.3∼27.6 in matrix-8 and circular-8 configurations. At these conditions, recirculation of burnt gas is related with stability augmentation. Fuel mole fraction measurements using laser induced fluorescence reveal lifted flame base is not located at the stoichiometric contour.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2000년도 제20회 KOSCO SYMPOSIUM 논문집
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• pp.1-8
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• 2000

The effects of nozzle arrangements, nozzle distances and fuel flowrates on the flame stabilities such as flame length, liftoff height and blowout characteristics are investigated experimentally. Three nozzle arrangements - diamond 4 nozzle, linear 5 nozzle, cross 5 nozzle- are used. Flame interactions result in the increase of the blowout flowrates and constant turbulent liftoff heights. The flames separated about 10 nozzle diameters are sustained as nozzle attached flames to the higher fuel flowrates than the other separation cases. Normally flames are extinguished at the lifted states. Blowout flowrates are affected by the nozzle configuration, nozzle seperation distance. Blowout flowrates for the diamond- or cross- shaped nozzle arrangements are parabolic function of nozzle distances. Maximum blowout flowrates for the 5 nozzle configuration case except linear one is about 2.9 times that of single equivalent nozzle case. Turbulent liftoff heights are not function of flowrates for the interacting flames.