• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.11
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• pp.1393-1402
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• 1997

Characteristics of the lifted flame which is generated by issuing of the fuel through the miniature nozzle, d = 0.164 mm, are studied using the planar laser induced fluorescence technique. OH radical is excited on the $Q_{1}$(8) line of the $A^{2}$.SIGMA.$^{+.leq.X2}$ .PI.(1, 0) band transition (283.55 nm) and LIF signals are captured at the bands of (0, 0) and (1, 1) transition (306 ~ 326 nm) using the filters and ICCD camera. Hydroxyl radical (OH) profile for nozzle attached flame shows that OH radical populations at the flame sides and flame tip are larger than those at the base. But for the lifted flame (tribrachial flame) case, those are larger at the flame base than at the flame tip and flame sides. The OH radical is more dense near the center line of flame base at the blowing out. This fact proves the Chung and Lee's blowout theory-blowout occurs when the flame is anchored at the flame axis. axis.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.453-456
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• 2011

An experimental investigation of the heat transfer characteristics of stretched premixed flames using Synthetic gas has been performed. Hydrogen and carbon mon-oxide which could be extracted from coal gasification process are the main fuel of synthetic-gas. Heat flux at the stagnation point was increased as global strainrate was increased, then the heat flux was decreased when a global strainrate reached a sudden point. Heat flux at the stagnation point is also affected by nozzle to impingement distance. Heat flux was increased as nozzle to impingement place distance was increased. This study is a foundation study of practical use of secondary gases from coals.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.2
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• pp.1-8
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• 2017

In order to analyze combustion characteristics of methane-oxygen diffusion flame in a model combustor, combustion experiments were carried out under various spray conditions of propellant scrutinizing combustion stability limit and flame shapes. As the propellant approached the theoretical equivalence ratio condition, a stable detached flame was observed even under high oxygen Reynolds number. And the length of the visible flame increased and the lift-off distance of the flame exhibited a tendency toward decrease. Due to the swirl effect of the propellant by the swirl-coaxial injector, a wide and short flame was produced. Thus, it may be appropriate to employ the swirl-coaxial injector in thrusters having a limited physical dimension.

• 한국가시화정보학회:학술대회논문집
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• 2005.04a
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• pp.61-83
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• 2005

연소현상의 가시화를 위한 몇 가지 레이저 진단기법의 응용 예를 소개한다. 이에는 유동 가시화를 위한 반응성 Mie 산란, 주화학종의 계측을 위한 Rayleigh 및 Raman 산란, 미소화학종 계측을 위한 레이저유도 형광법, 온도계측을 위한coherent anti-Stokes Raman 산란법 및 매연계측을 위한 광 소멸/산란법 등이 포함된다. 이러한 기법들이 확산화염, 층류 및 난류 부상 화염, 비예혼합 와도 내의 화염전파, 매연생성 등의 연구에 적용되어 물리적 메커니즘을 이해하는데 유용하게 적용된 사례를 보고한다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.8
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• pp.761-766
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• 2010

The estimation method of the interchangeability in a partial premixed appliance about various compositions of natural gases using equivalent gases, experimentally. The results of the experiment in which equivalent gases were used compared with those obtained in experiments in which natural gases were used; Images of flames, lift-off limits, CO emissions, and incomplete combustion indices in KS standard for the domestic gas range were considered. From the comparison, it was observed that the length and color of the flame of the equivalent gases were almost the same as those of imported natural gases. Further, in the case of gases with Wobbe indices greater than 51 MJ/$m^3$, the KS standard for lifting limits was satisfied. Furthermore, in the case of gases with Wobbe indices less than 56.3 MJ/$m^3$, the CO mole fractions are in the range 95-100 ppm. Hence, the range of Wobbe indices 51-56.3 MJ/$m^3$ was proposed to be the range for interchangeability from the points of view of lifting limits and incomplete combustion, as prescribed in the domestic gas range in the case of imported natural gases.

• 한국연소학회:학술대회논문집
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• 2004.11a
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• pp.85-90
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• 2004

We have presented characteristics of a transitional behavior from a premixed flame to a triple flame in a lifted flame according to the change of equivalence ratio. The experimental apparatus consisted of a slot burner and a contraction nozzle for a lifted flame. As concentration difference of the both side of slot burner increases, the shape of flame changed from a premixed flame to a triple flame, and the liftoff height is decreased to the minimum value and then increase again. Around this minimum point, it is confirmed a transition regime from premixed flame to triple flame. Consequently, the experimental results of the liftoff height, flame curvature and luminescence intensity showed that the stabilized laminar lifted flame regime is categorized by regimes of premixed flame, triple flame and critical flame. In the visualization experiment of smoke wire, the flow divergence and redirection reappeared in premixed flame as well as triple flame. Thus we cannot express the flame front of lifted flame has a behavior of triple flame with only flow divergence and redirection. To differentiate triple flame and premixed flame, ${\Phi}$ value of partially premixed fraction is employed. The partially premixed fraction ${\Phi}$ was constant in premixed flame. In critical flame small gradient appears over the whole regime. In triple flame, typical diffusion flame shape is obtained as parabolic distribution type due to diffusion flame trailing.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.2
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• pp.204-215
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• 2011

Flame stability is the one of the main mechanism of laminar lifted flame and flame propagation velocity becomes a yardstick to measure the flame stability. Bilge has presented the flame propagation velocity of the triple flame and the flame stability mechanism related the flame configuration and mixture fraction. However, there was not able to observe all process of flame ignition and extinction for small nozzle diameter. In this paper, we have subdivided the flame configuration and stability mechanism and classified the flame behavior with a nozzle diameter. Also we have subdivided the 'triple flame propagation opened' and the 'triple flame propagation closed' from the triple flame propagation of triple flame criterion.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.10
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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.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2012.04a
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• pp.258-261
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• 2012

풀화재에서 화염화염진동은 주위공기와의 밀도차에 의한 부력효과에 기인하여 주로 발생한다. 본 연구는 풀화재의 화염불안정성에 대해 산화제 유속 및 농도 변화에 따른 효과를 검토하기 위하여 컵버너 실험을 수행하였다. 실험결과는 산화제의 농도를 변화시켰을 경우에는 산화제의 불활성기체의 농도가 증가할수록 청염의 길이가 길어지고 컵버너 끝단으로부터 부상되는 것이 관찰된다. 한편, 산화제의 유속이 증가함에 따른 진동주파수가 감소함을 보인다. 이는 무차원 변수로 표현되는 주파수와 부력의 관계로 도시하였을 때 다양한 속도스케일을 사용할 수 있었지만, 연료와 산화제의 유속차로 정의되는 특성속도인 경우에 정지되어 있는 공기중에서의 풀화재 진동과 일치하는 관계식을 얻을 수 있었다. 그리고 진동주파수는 산화제 희석율과는 특정한 관계를 보이지 않는데 이는 국부적 화염구조와 연관성을 가지기 때문으로 판단된다.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2372-2377
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• 2007

Characteristics of turbulent lifted flames in coflow jets with the varying initial temperature have recently been investigated about only propane case diluted by nitrogen. The investigation has firstly improved a premixed flame model and a large scale mixing model among competing theories on the stabilization mechanism of turbulent flame to be suitable for a high temperature condition. In this research, about methane with good availability to apply for a practical combustor as clean fuel, its characteristics of turbulent nonpremixed flame have been studied experimentally. The results have shown an effectiveness of the premixed flame model and the large scale mixing model considered initial temperature variation. Additionally, considering the axial distance where the mean fuel concentration falls below the stoichiometric level along the center line of the jet according to diluting nitrogen, the premixed flame model have more accurately been improved.