• 대한기계학회논문집B
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• 제27권8호
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• pp.1089-1096
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• 2003

An experiment was performed to investigate lift-off, blow-off and combustion characteristics of a lifted coaxial diffusion flame according to fuel jet and air velocity. A jet diffusion flame which is attached on the nozzle rim begins to be lifted with increase of air velocity, and finally becomes blow-off at higher air velocity. In experiment, blow-off limit increased with increase of fuel jet velocity, however lift-off occurred at lower air velocity. Flame structure and combustion characteristics were examined by schlieren photos, temperature distributions and emission concentration distributions. Flame temperature became higher at midstream and its RMS became larger at up and downstream with increase of air velocity. Local NO concentration decreased but $CO_2$concentration increased with increase of air velocity, which shows combustion reaction becomes close to be stoichiometric at higher air velocity in spite of lift-off.

• 한국분무공학회지
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• 제8권4호
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• pp.24-30
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• 2003

This paper presents the characteristics of lifted height and flame length from non-premixed jet flames in highly preheated air to investigate the detail combustion mechanism in the gas turbine or HCCI engine, etc. Special attention was paid to the effect of preheated air temperature, oxygen concentration and fuel injection flow rate on flame length and lifted hight. By using highly preheated air, stable flames were formed even in low oxygen concentration condition. The lifted height increased with decreasing preheated air temperature, where the flame length showed opposed phenomena. The flamelet model, which is thought to have very thin flamelet, is difficult to applicable to the present flame conditions which is formed In low oxygen concentration in highly preheated air.

• 한국추진공학회지
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• 제21권2호
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• pp.1-8
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• 2017

본 연구에서는 모델연소실 내부 메탄-산소 확산화염의 연소특성을 분석하기 위해 추진제의 다양한 분사조건에서 연소실험을 수행하여 연소안정한계 측정 및 화염의 형상변이를 관찰하였다. 연구 결과, 추진제가 이론당량비 조건으로 접근할수록 높은 산소 Reynolds 수($Re_o$) 구간에서도 안정적인 부상화염이 관찰되었으며, 가시화염의 길이는 증가하고, 부상높이는 감소하는 경향이 나타났다. 스월 동축형 인젝터에 의한 추진제의 스월효과로 인해 폭이 넓고, 길이가 짧은 화염이 생성되어 연소실 크기가 제한적인 추력기에서의 사용이 적합함을 확인하였다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제29회 KOSCI SYMPOSIUM 논문집
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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.

• 대한기계학회논문집B
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• 제37권9호
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• pp.829-836
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• 2013

석탄을 개질한 합성천연가스의 조성에 변화가 있을 경우 화염의 연소특성에 대하여 연구하였다. 본 연구의 목적은 동축 공기 합성천연가스 확산화염을 구현하여 연료조성에 따른 화염안정성과 화염구조, 분광특성, 온도분포를 실험적인 방법으로 연구하는 것이다. 각 화염의 분광특성을 관찰하기 위하여 분광기를 사용하였으며 연소장 내 온도측정을 위하여 K 형 열전대를 사용하였다. 연료 분사기 출구속도는 $u_F$ =5~40 m/s 사이에서 조절하였고 공기 분사기 출구속도는 $u_A$ =0~0.43 m/s 사이에서 조절하였다. 연소 동특성에 대한 실험을 통해 합성천연가스에 수소 성분이 증가하면 화염안정화 영역이 증가하고 부상화염 높이가 낮아져 화염길이가 짧아지는 것을 알 수 있었다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2007년도 제34회 KOSCO SYMPOSIUM 논문집
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• pp.13-18
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• 2007

When triple flames propagated in a diverging channel, the effects of fuel dilution on the lift-off characteristics of triple flames were investigated. A multi-slot burner was used to stabilize the lift-off flame especially at weak fuel concentration gradients. It was reported that there is a maximum propagation velocity at a critical concentration gradient in an open jet regardless of fuel dilution. The enhancement of a diffusion flame affected to increase the propagation velocity around critical concentration gradients. However, the influence of a confined channel on the structure of triple flames according to fuel dilution needs to be investigated compared with an open jet case. This study aimed to examine the effect of a confined channel on the structure and the propagation velocity of the triple flames according to fuel dilution. Lift-off height and propagation velocity of triple flames were investigated by employing three kinds of fuel compositions diluted by nitrogen (0%, 25%, 50% $N_2$), Fuel dilution reduced the propagation velocity of triple flame in a confined channel mainly due to the decrease of flame temperature in premixed branch. Despite the difference in fuel dilution, the propagation velocity has a maximum value at a specific fuel concentration gradient even though the critical concentration gradient increases with fuel dilution. And the critical concentration gradient in a confined channel is larger than that in an open jet due to enhancement of convective diffusion.

• 한국연소학회지
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• 제22권3호
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• pp.17-22
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• 2017

An experimental study has been conducted to elucidate the effect of AC electric field on behaviors of laminar lifted flame in nitrogen-diluted methane coflow-jets. Our concerns are focued on the regime to show a decrease in liftoff height, $H_L$ with increasing nozzle exit velocity, $U_O$ (hereafter, $decreasing-H_L$). The $H_L$ with $U_O$ near flame extinction were measured by varying the applied AC voltage, $V_{AC}$ and frequency, $f_{AC}$ in a single electrode configuration. The behavior of $H_L$ with a functional dependency of $V_{AC}$ and $f_{AC}$ was categorized into two regime : (I) $H_L$ decreased for nozzle diameter, D = 1.0 mm, and (II) $H_L$ increased in the increase of $f_{AC}$ for a fixed $V_{AC}$ in a D = 4.0, 8.4 mm. The lifted flames in $decreasing-H_L$ region was unstable in high voltage regimes while the $H_L$ showed a decreasing tendency with $U_O$ except them. Such behaviors in $H_L$ were also characterized by functional dependencies of related physical parameters such as $V_{AC}$, $f_{AC}$, $U_O$, fuel mole fraction ($X_{F.O}$) and D.