• Journal of the Korean Society of Combustion
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• v.6 no.2
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• pp.23-28
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• 2001

In the present work, the effect of PDF selection and intermittency on the result of the numerical simulation are examined by the simulation of a turbulent methane-air jet diffusion flame. As to the PDFs, beta-function and clipped Gaussian are considered. Results for the pure mixing jet are compared with experimental results. Then, the turbulent flame is calculated for the same conditions and the results obtained for the several models are compared. It is found that the clipped Gaussian distribution coupled with consideration of intermittency recovers the experimental data very well. As to the reacting flow results, the main overall properties of the turbulent jet diffusion flame such as maximum flame temperature are less affected by the choice of the PDF. Flame height and NO emissions, on the contrary, appear to be significantly influenced.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.12
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• pp.1662-1669
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• 2000

Various flame types are observed in a double concentric burner by varying equivalence ratio and flow rates in each tube. Observed flame types include bunsen-type flame, ring-shaped flame, outer lifted flame, inner lifted flame, and oscillatory lifted flame, The doman of existence of various flames is mapped with equivalence ratio and annular jet velocity. Each flame is investigated through direct photography and OH PLIF. As central air velocity increase, the blowout region is diminished and lifted oscillating flames are observed. Inner lifted flames are observed from bunsen flames or rich shaped flames by increasing central air velocity. For inner lifted flames, annular jet velocity, at flame liftoff decreases with increasing central air jet velocity. Axial velocity profile and temperature fie이 using LDV and CRS, respectively, for a typical inner lifted flame are also measured through which the role of tribrachial flame for stabilization in emphasized.

• 한국연소학회:학술대회논문집
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• 2004.11a
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• pp.70-75
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• 2004

The effect of electric fields on the stability of non-premixed laminar lifted flame in coflow jets has been investigated by applying high voltage alternative current (AC) to the nozzle of propane fuel. The stable lifted flame which exist in far field of jets, the liftoff height was not effected by applied voltage. This implies that the cold jet between the nozzle and flame base can be analyzed with the previous cold jet theory. Flame liftoff and reattachment velocities were also measured as function of applied voltage and frequency. The fuel jet velocity at flame liftoff and reattachment increased with increasing voltage, implying that the range of flame srability can be extended with the AC charging. However the liftoff velocity increased with frequency of AC charging on nozzle, whereas the reattachment velocity decreases with frequency. The liftoff and reattachment velocities were correlated linearly with voltage considering the effects of frequency.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.2
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• pp.175-184
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• 1999

A theoretical study on the turbulent round jet diffusion flame impinging on the wall was carried out to predict the characteristics and structure of Impinging jet flame and heat transfer to the wall. Finite chemistry via Arrhenius equation and eddy dissipation model was adopted as a combustion model, and the Favre averaging and $k-{\varepsilon}$ model were Introduced In the theoretical modeling. The SIMPLE algorithm was applied to the calculation. All the transport properties were considered as the variable depending on the temperature and composition. For the parametric study, the distance from nozzle to impinging wall and Reynolds number at nozzle exit were chosen 88 the major parameters. As the results of the present study, the characteristics of flow fields, the distributions of main variables and each chemical species and the flame shapes were obtained. The heat transfer rate from the flame to the wall and the effective heating area were calculated to investigate the Influences of the major parameters on the heat transfer characteristics.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2712-2723
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• 1994

Numerical simulation of an axisymmetric ethylene-air jet diffusion flame has been carried out in order to investigate flame dynamics and soot formation. The model solves the time-dependent Navier-Stokes equations and includes models for soot formation, chemical reaction, molecular diffusion, thermal conduction, and radiation. Numerically FCT(Flux Corrected Transport) and DOM(Discrete Ordinate Method) methos are used for convection and radiation trasport respectively. Simulation was conducted for a 5 cm/sec fuel jet flowing into a coflowing air stream. The maximum flame temperature was found to be approximately 2100 K, and was located at an axial position of approximately 5 cm from the base of the flame. The maximum soot volume fraction was about $7{\times}10^{-7}$, and was located within the high temperature region where the fuel mole fraction ranges from 0.01 to 0.1. The buoyancy-driven low-frequency(12~13 Hz) structures convected along the outer region of the flame were captured. In case without radiation trasport, the maximum temperature was higher by 150 K than in case with radiation. Also the maximum soot volume fraction reached about $8{\times}10^{-6}$. As the the hydrocarbon fuel forms many soot particles, the radiation transport becomes to play a more important role.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.3
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• pp.578-588
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• 1992

In order to predict the effect of swirl on the structure of concentric laminar jet diffusion flame, present study examined the effect of swirl on the flame characteristics by numerical numerical analysis through theoretical model. The theoretical model has been developed for the co-axial laminar jet flame such that the fuel and air are supplying with swirl through inner and outer co-axial tube respectively. For the parametric study, swirl number, Reynolds number of fuel and air and directions of swirl are chosen as important parametes. The results of study show that the flame with width and shorter length is formed by larger swirl number. The important factor of the flame shape is the recirculating zone formed around jet axis near the exit of nozzle. In case of weak swirl, the effect of directions of swirl is not appeared. However, for the strong swirl, the flame with shorter length are appeared in case of counter-swirl compared with the case of co-swirl.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.7
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• pp.477-485
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• 2009

The study of nitrogen dilution effect on the flame stability was experimentally investigated in a non-premixed turbulent lifted hydrogen jet with coaxial air. Hydrogen gas was used as a fuel and coaxial air was used to make flame liftoff. Each of hydrogen and air were injected through axisymetric inner and outer nozzles ($d_F=3.65\;mm$ and $d_A=14.1\;mm$). And both fuel jet and coaxial air velocity were fixed as $u_F=200\;m/s$ and $u_A=16\;m/s$, while the mole fraction of nitrogen diluents gas was varied from 0.0 to 0.2 with 0.1 step. For the analysis of flame structure and the flame stabilization mechanism, the simultaneous measurement of PIV/OH PLIF laser diagnostics had been performed. The stabilization point was selected in the most upstream region of the flame base and defined as the point where the turbulent flame propagation velocity was equal to the axial component of local flow velocity. We found that the turbulent flame propagation velocity increased with the decrease of nitrogen mole fraction. We concluded that the turbulent flame propagation velocity was expressed as a function of turbulent intensity and axial strain rate, even though nitrogen diluents mole fraction was changed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.8
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.2
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• pp.160-166
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• 2004

Combustion using oxygen enriched air is known as a technology which can increase flame stability as well as thermal efficiency due to improving the burning rate. Lift-off, blowout limit and flame length were examined as a function of jet velocity, coflow velocity and OEC(Oxygen Enriched Concentration). Blowout limit of the flame below OEC 25% decreased with increase of coflow velocity, but the limit above OEC 25% increased inversely. Lift-off height decreased with increase of OEC. In particular, lift-off hardly occurred in the condition above OEC 40%. Flame length of the flames above OEC 40% was increased until the blowout occurred. Great flame stability was obtained since lift-off and blowout limit significantly increased with increase of OEC.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.326-331
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• 2003

Combustion using oxygen enriched air is known as a technology which can increase flame stability as well as thermal efficiency due to improvement of the burning rate. Lift-off, blowout limit and flame length were examined as a function of jet velocity, coflow velocity and OEC(Oxygen Enriched Concentration). Blowout limit of the flame below OEC 25% decreased with coflow velocity, but the limit above OEC 25% increased inversely. Lift-off height decreased with increase of OEC. Especially lift-off hardly occurred in the condition above OEC 40%. Flame length of the flames above OEC 40% was increased until the blowout occurred. Flame stability became improved since lift-off and blowout limit increased much with increase of OEC.