• 한국연소학회지
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• 제21권2호
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• pp.22-28
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• 2016

High efficient and environment friendly combustion technologies are used to be operated an extreme condition, which results in unintended flame instability such as extinction and oscillation. The use of electromagnetic energy is one of methods to enhance the combustion stability and a microwave as electromagnetic wave is receiving increased attention recently because of its high performance and low-cost system. In this study, an experiment was performed with jet diffusion flames induced by microwave. Micro jet was introduced to simulate the high velocity of industrial combustor. The results show that micro jet flames had three different modes with increasing oxidizer velocity; attached yellow flame, lifted flame, and lifted partially premixed flame. As a microwave was induced to flames, the overall flame stability and blowout limit were extended with the higher microwave power. Especially the interaction between a flame and a microwave was shown clearly in the partially premixed flame, in which the lift-off height decreased and NOx emission measured in post flame region increased with increasing microwave power. It might be attributed to increase of reactivity due to the abundance of radical pool and the enhanced absorption to thermal energy.

• 대한기계학회논문집B
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• 제35권10호
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• pp.1025-1031
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• 2011

자발화 특성은 디젤 및 PCCI 엔진의 설계에서 중요한 인자이다. 특히, 디젤분무화염은 자발화현상에 의해서 형성되어 노즐에서 부상된다. 노즐과 부상화염 사이의 영역에서 분무된 디젤의 중앙으로 주위 공기의 유입이 발생하기 때문에, 그 부상된 화염은 매연 생성에 영향을 준다. 본 연구에서 간단한 모델로써 동축류 제트를 적용하였고, 점화지연시간에 대한 자발화 과정에서 발생하는 열손실의 영향을 확인하였다. 메탄($CH_4$), 에틸렌($C_2H_4$), 에탄($C_2H_6$), 프로핀($C_3H_6$), 프로판($C_3H_8$), 및 노말 부탄(n-$C_4H_{10}$)의 연료들을 고온의 공기로 분사하였으며 자발화된 부상화염의 높이를 측정하였다. 그 결과로 자발화된 부상화염의 높이와 열손실을 고려한 점화지연시간과의 상관관계를 결정하였다.

• 한국수소및신에너지학회논문집
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• 제28권2호
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• pp.181-189
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• 2017

This paper describes experimental results on combustion characteristics with hydrogen contents of synthetic natural gas (SNG) in low swirl combustor. To investigate the effect of hydrogen contents for premixed SNG flame, stability map, CH chemiluminescence images, flame spectrum analysis and emission performances were measured. In the results, as the hydrogen content was increased, the lean flammable limit was expanded and the flame length was decreased. The hydrogen contents affected the flame liftoff height, and it has different tendency according to the equivalence ratio and flame shape. The change of height and length of flame according to hydrogen contents is caused by the fast burning velocity of hydrogen, which can be confirmed by GRI 3.0 reaction mechanism in PREMIX code. The intensity of $OH^*$, $CH^*$ and $C_2^*$ was confirmed by spectrum analysis of flame. As a result, the $CH^*$ intensity was not significantly different according to hydrogen content. The increase of hydrogen contents influenced positively CO and NOx emission performances.

• 대한기계학회논문집B
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• 제29권3호
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• pp.376-383
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• 2005

In the paper we investigate characteristics of a transitional behavior from a premixed flame to a triple flame in a lifted flame according to the change of equivalence ratio. In previous study, we showed that the stabilized laminar lifted flame regime is categorized by regimes of premixed flame, triple flame and critical flame. A gas-chromatograph is used to measure concentration field, a smoke-wire system is used to measure streak line, and a PIV system is used to measure velocity field in lifted 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. In PIV measurement, flow velocity for those three flames has minimum value at the tip of flame front. 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.

• 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.

• 한국연소학회지
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• 제4권1호
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• pp.1-15
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• 1999

In order to analyze the sensitivity on the pulverized coal flames of the several variables, a numerical study was conducted at the gasification process. Eulerian approach is used for the gas phase, whereas lagrangian approach is used for the solid phase. Turbulence is modeled using the standard $k-{\varepsilon}$ model. The turbulent combustion incorporates eddy dissipation model. The radiation was solved using a Monte-Carlo method. One-step two-reaction model was employed for the devolatilization of Kideco coal. In pulverized flame of long liftoff height, the initial turbulent intensity seriously affects the position of flame front. The radiation heat transfer and wall heat loss ratio distort the temperature distributions along the reactor wall, but do not influence the reactor performance such as coal conversion, residence time and flame front position. The primary/secondary momentum ratio affects the position of flame front, but the coal burnout is only slightly influenced. The momentum ratio is a variable only associated with the flame stabilization such as flame front position. The addition of steam in the reactor has a detrimental effect on all the aspects, particularly reactor temperature and coal burnout.

• 한국항공우주학회지
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• 제36권4호
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• pp.352-356
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• 2008

수소제트와 동축공기를 사용한 본 연구에서, 난류확산화염의 화염안정성 특징을 실험적으로 수행하였다. 목적은 연료속도 증가에 따라 감소하는 부상화염길이의 경향을 보고하고, 부상 메커니즘을 포함한 화염구조를 분석하는 것이다. 수소연료는 100에서 300 m/s 사이에서 조절되었으며, 이때 동축공기는 16 m/s 고정되고, 주위류는 0.1 m/s 이하로 유지되었다. 유동장과 연소장 동시측정을 위하여, 두 대의 Nd:Yag 레이저와 CCD 카메라를 이용하여 PIV와 OH PLIF 기법이 사용되었다. 결론적으로 난류화염전파속도는 난류강도에 비례하였으며, 제트 레이놀즈수의 0.017승에 비례하였다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
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• pp.349-352
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• 2008

This study has numerically modeled the combustion processes of the turbulent swirling premixed lifted syngas flames in the low-swirl burner (LSB). In these turbulent swirling premixed flames, the four tangentially-injected air jets induce the turbulent swirling flow which plays the crucial role of stabilizing the turbulent lifted flames. In the present approach, the turbulence-chemistry interaction is represented by the level-set based flamelet model. Numerical results indicate clearly that the present level-set based flamelet approach has realistically simulated the structure and stabilization mechanism of the turbulent swirling premixed lifted flames in the low-swirl burner. Computations are made for the wide range of the syngas chemical composition and the dilution level at two pressure conditions (1.0, 5.0 bar). Numerical results indicate that the lifted height in the LSB is increased by decreasing the H2 percentage and increasing the dilution level at the given equivalence ratio. It is also found that the flashback is occurred for the hydrogen composition higher than 80% at the equivalence ratio, 0.8. However, at the syngas composition range in the IGCC system, the stable lean-premixed lifted flames are formed at the low-swirl burner.