• Journal of Mechanical Science and Technology
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• 제16권4호
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• pp.564-571
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• 2002

Three-dimensional numerical analysis of the turbulent premixed flame propagation in a constant volume combustion chamber is performed using the KIVA-3V code (Amsden et. al. 1997) by the flame surface density (FSD) model. A simple near-wall boundary condition is eaployed to describe the interaction between turbulent premixed flame and the wall. A mean stretch factor is introduced to include the stretch and curvature effects of turbulence. The results from the FSD model are compared with the experimental results of schlieren photos and pressure measurements. It is found that the burned mass rate and flame propagation by the FSD model are in reasonable agreement with the experimental results. The FSD combustion model proved to be effective for description of turbulent premixed flames.

• 한국연소학회지
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• 제7권3호
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• pp.47-54
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• 2002

The propagation speed of tribrachial flame in laminar propane jets has been investigated experimentally under normal and micro gravity conditions. The displacement speed was found to vary nonlinearly with axial distance because flow velocity along stoichiometric contour was comparable to the propagation speed of tribrachial flame for the present experiment. Approximate solutions for velocity and concentration accounting density difference and virtual origins have been used in determining the propagation speeds of tribrachial flame. Under micro gravity condition, the results showed that propagation speed of tribrachial flame is largely affected by the mixture fraction gradients, in agreement with previous studies. The limiting maximum value. of propagation speeds under micro gravity conditions are in good agreement with the theoretical prediction, that is, the ratio of maximum propagation speed to the stoichiometric laminar burning velocity is proportional to the square root of the density ratio of unburned to burnt mixture.

• Journal of Advanced Marine Engineering and Technology
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• 제34권2호
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• pp.250-258
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• 2010

부상화염에서 노즐직경과 연료유량을 변화하면서 화염전파속도와 연료과농영역, 연료희박영역, 확산화염 영역에서의 체적연소반응속도의 변화 특성을 수치해석을 통하여 살펴보았다. 본 연구에서 사용한 3가지 연료노즐 직경(d=0.25, 0.30, 0.35mm)에서 연료분출속도를 증가시키면 화염전파속도가 증가하지만 변화폭은 4.3%를 넘지 않는다. 연료분출속도를 증가함에 따른 연료량 증가는 직접적이고 선형적으로 체적연소반응속도에 연관되어 있음을 알 수 있었고, 따라서 부상화염에서 연료량의 증가는 화염전파속도 보다 체적연소반응속도가 연료량 변화에 대응함을 알 수 있었다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제28회 KOSCO SYMPOSIUM 논문집
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• pp.102-111
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• 2004

Partial quenching structure of turbulent diffusion flames in a turbulent mixing layer is investigated by the method of flame hole dynamics to develope a prediction model for the turbulent lift off. The present study is specifically aimed to remedy the problem of the stiff transition of the conditioned partial burning probability across the crossover condition by adopting level-set method which describes propagating or retreating flame front with specified propagation speed. In light of the level-set simulations with two model problems for the propagation speed, the stabilizing conditions for a turbulent lifted flame are suggested. The flame hole dynamics combined with level-set method yields a temporally evolving turbulent extinction process and its partial quenching characteristics is compared with the results of the previous model employing the flame-hole random walk mapping. The probability to encounter reacting' state, conditioned with scalar dissipation rate, demonstrated that the conditional probability has a rather gradual transition across the crossover scalar dissipation rate in contrast to the stiff transition of resulted from the flame-hole random walk mapping and could be attributed to the finite response of the flame edge propagation.

• 한국연소학회지
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• 제1권1호
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• pp.65-73
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• 1996

Flame propagation in a four-valve spark-ignition optical engine was visualized under lean-bum conditions with A/F=18 at 2000rpm. The early flame development in a four-valve pentroof-chamber single-cylinder engine was examined with imaging of the laser-induced Mie scattered light using an image-intensified CCD camera. Flame profiles along the line-of-sight were also visualized through a quartz piston window. Two-dimensional flame structures were visualized with a Proxitronic HF-1 fast motion camera system by Mie scattering from titanium dioxide particles along a planar laser sheet generated by a copper vapor laser. The flame propagation images were subsequently analysed with an image processing programme to obtain information about the flame structure under different tumble flow conditions generated by sleeved and non-sleeved intake ports. This allowed enhancement of the flame images and calculation of the enflamed area, and the displacement of its center, as a function of the tumble flow induced by the pentroof-chamber in the vicinity of spark plug. Image processing of the early flame development quantified the correlation between flame and flow characteristics near the spark plug at the time of ignition which has been known to be one of the most important factors in cyclic combustion variations in lean-burn engines. The results were also compared with direct flame images obtained from the natural flame luminosity of the lean mixture.

• 한국연소학회지
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• 제9권2호
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• pp.18-29
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• 2004

Partial quenching structure of diffusion flames in a turbulent mixing layer has been investigated by the method of flame hole dynamics in oder to develope a prediction model for the phenomenon of turbulent flame lift off. The present study is specifically aimed to remedy the shortcoming of the stiff transition of the conditioned partial burning probability across the crossover condition by employing the level-set method which enables us to include the effect of finite flame edge propagation speed. In light of the level-set simulation results with two models for the edge propagation speed, the stabilizing conditions for turbulent lifted flame are suggested. The flame hole dynamics combined with the level-set method yields a temporally evolving turbulent extinction process and its partial quenching characteristics is compared with the results of the previous model employing the flame-hole random walk mapping based on three critical scalar dissipation rates. The probability to encounter reacting state, conditioned with scalar dissipation rate, demonstrated that the conditional probability has a rather gradual transition across the crossover scalar dissipation rate. Such a smooth transition is attributed to the finite response of the flame edge propagation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.422-427
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• 2000

Propagation characteristics of tribrachial flames have been investigated experimentally in both two-dimensional and axisymmetric counterflows. Mixture fraction gradient at stoichiometric location is controlled by varying equivalence ratios at the two nozzles, one of which maintains rich while the other lean premixture. Tribrachial flames propagating through these mixtures are investigated. The propagation speed of tribrachial flames in two-dimensional counterflow decreases with fuel concentration gradient and has much higher speed than the maximum speed predicted previously in two-dimensional mixing layers. From an analogy with premixed flame propagation, this excessively large propagation speed can be attributed to the tribrachial flame propagating with respect to burnt gas. Corresponding maximum speed in the limit of small mixture fraction gradient is estimated and extrapolated experimental results substantiate this limiting speed. As mixture fraction gradient approaches zero, a transition in propagation characteristics occurs, such that the propagation speed of tribrachial flame approaches stoichiometric laminar burning velocity with respect to burnt gas. Similar behavior has been obtained for tribrachial flames propagating in axisymmetric counterflow.

• 한국자동차공학회논문집
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• 제3권2호
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• pp.136-145
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• 1995

The aim of this study is to gain a better understanding of the effect of a flow motion on the flame development by means of an optically-accessible constant-volume combustion chamber and the visualization technique of a combustion flame. At first, the characteristics of a flame propagation are investigated in the combustion field of the two kinds of flow conditions such as a quiescent and a flowing condition, and methane-air mixture is used as fuel. Then the same investigation is performed in two flow configurations : bulk flow motion type and turbulence generating type. In this study, the combustion phenomena are analyzed by measuring the combustion pressure, flame propagation speed, mean velocity, turbulent intensity, and mass fraction burned.

• 대한기계학회논문집
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• 제19권6호
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• pp.1510-1517
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• 1995

A theoretical method is described to simulate the propagation of turbulent premixed flames in a closed vessel. The objective is to develop and test an efficient technique to predict the propagation speed of flame as well as the geometric structure of the flame surfaces. Flame is advected by the statistically generated turbulent flow field and propagates as a wave by solving twodimensional Hamilton-Jacobi equation. In the simulation of the unburned gas flow field, following turbulence properties were satisfied: mean velocity field, turbulence intensities, spatial and temporal correlations of velocity fluctuations. It is assumed that these properties are not affected by the expansion of the burned gas region. Predictions were compared with existing experimental data for flames propagating in a closed vessel charged with hydrogen/air mixture with various turbulence intensities and Reynolds numbers. Comparisons were made in flame radius growth rate, rms flame radius fluctuations, and average perimeter and fractal dimensions of the flame boundaries. Two dimensional time dependent simulation resulted in correct trends of the measured flame data. The reasonable behavior and high efficiency proves the usefulness of this method in difficult problems of flame propagation such as in internal combustion engines.

• 한국추진공학회지
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• 제16권6호
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• pp.1-8
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• 2012

본 연구에서는 정상초음파의 간섭에 의해 야기되는 프로판/공기 예혼합화염의 사각관내 전파거동 및 구조안정화를 규명하기 위한 실험결과를 제시한다. 전파화염의 이미지는 고속카메라를 이용하여 획득하였으며, 이미지 후처리를 통해 정상초음파 유무에 따른 화염선단의 구조변이와 전파속도를 상세히 관찰하였다. 전파속도는 정상초음파가 교반하는 경우 증가하였으며, 이론당량비에서 벗어남에 따라 초음파의 영향은 보다 크게 발현하였다. 정상초음파에 의한 화학반응과 혼합의 촉진은 화염선단의 형상에 대한 부력의 영향을 압도하여 화염의 구조적 안정화에 기여한다.