• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.115-116
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• 2015

In the present approach, the flame-acoustics interaction is represented by FDF (Flame Describing Function) which is a important source term in the Helmholtz' equation. In this study, the combustion instability is analyzed by the forced mode strategy with the measured FDF. Numerical results indicate that the present approach reasonably well predicts the essential features of the combustion instability characteristics in the lean premixed combustor under the gas-turbine like environment.

• 한국연소학회:학술대회논문집
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• 2002.06a
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• pp.179-184
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• 2002

Interaction between flames and non-thermal plasmas of DBD type has been experimentally investigated. Vigorous streamers were observed under flame conditions because of the increase of reduced field (electrical) at high temperature as well as the seeding of free electrons and ions generated inside the flame. Flame lengths were significantly shortened as the applied voltage increased on account of intense mixing by ionic winds and soot-induced flows. Flame luminosities severely decreased under plasma conditions, which means the reduction of soot, since the residence time was reduced because of the flame shortening. Temperature and major species concentrations measured by FTIR were not changed despite the plasma generation. which shows overall chemistries were not affected by non-thermal plasmas.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.6 s.237
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• pp.730-736
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• 2005

It has been reported that the interacting multiple jet flames of propane fuel are not extinguished even at the choking velocity at the nozzle exit if eight small nozzles are arranged along the imaginary circle of $40{\sim}72$ times the diameter of single nozzle. In this research, experiments were conducted to know the NO and CO emission characteristics of the interacting flames. Measurements along the centerline of the flame revealed that decrease in CO concentration was followed by the NO decrease and $O_2$ increase. It was found that interacting flame emitted less NO than that of similar area single jet flame. Also, NO emission of partially premixed interacting flame was decreased up to $17\%$ of that of non-premixed multiple jet flame. Though the mechanism of the NO reduction was not clear from this experiment, it's been shown that partially premixed multiple jet flames could be used to achieve clean and highly stable combustion.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.12
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• pp.1669-1680
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• 1998

A method is developed to include the effect of volume expansion in the description of the flame dynamics using G-equation. Line volume-source is used to represent the effect of the exothermic process of combustion with source strength assigned by the density difference between the burned and the unburned region. The present model provides good agreement with the experimental results. Including volume expansion, the flow field is adjusted to accommodate the increased volume flow rate which crossing the flame front and the result predicts the same behavior of measured velocity field qualitatively. The effect of increasing volume expansion does not change the initial growth rate of flame area but increase the residence time. Consequently this effect increases the maximum area of flame front. The flame propagation in varying flow field due to volume expansion provides a promising way to represent the wrinkled turbulent premixed flames in a numerically efficient manner.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.159-162
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• 2012

Combustion in a narrow space has been interested as a model of meso-scale combustors (or micro-combustors). Premixed flames have been used to overcome flame quenching in a narrow space and non-premixed flames have been used to improve flame stabilization. In this study, overall characteristics of premixed flame and non-premixed flame in narrow combustion spaces were reviewed. Various effects such as the flow velocity distribution, thermal interaction, enhanced mass diffusion were discussed and an eventual structure of the flame at the extinction limit was introduced.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.10
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• pp.1401-1411
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• 2003

A two-dimensional direct numerical simulation was performed to investigate the flame structure of CH$_4$$N_2$-air counterflow nonpremixed flame interacting with a single vortex. The detailed transport properties and a modified 16-step augmented reduced mechanism based on Miller and Bowman's detailed chemistry were adopted in this simulation. The characteristic vortex and chemical time scales were introduced to quantify and investigate the extinction phenomenon during a flame-vortex interaction. The results showed that fuel- and air-side vortex cause an unsteady extinction. In this case, the flame interacting with a vortex was extinguished at much larger scalar dissipation rate than steady flame. It was also found that the air-side vortex extinguished a flame more rapidly than the fuel-side vortex. Furthermore, it was noted that the degree of unsteady effect experienced by a flame can be investigated by comparing the above two characteristic time scales, and this analysis could give an appropriate reason for the results of the previously reported experiment.

• 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.

• Journal of the Korean Society of Combustion
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• v.23 no.1
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• pp.36-43
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• 2018

Numerical simulations and experiments are performed to investigate the flame development inside tubes with different diameters at the same burst pressure. It is shown that generation of a stable flame play a role in self-ignition. In the smaller tube, multi-dimensional shock interaction is occurred near the diaphragm. After flame of a cross-section is developed, stable flame remains for a moment then it grows having enough energy to overcome the sudden release at the exit. Whereas shock interaction generate complex flow further downstream for a larger tube, it results in stretched flame. This dispersed flame has lower average temperature which makes it easily extinguished.

• Journal of the Korean Society of Combustion
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• v.15 no.1
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• pp.38-42
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• 2010

Using a counterflow burner, downstream interactions between $CH_4$-air and $H_2/N_2$-Air premixed flames with various equivalence ratios has been experimentally investigated. Flame stability maps on triple and twin flames are provided in terms of global strain rate and equivalence ratio. Lean and rich flammable limits are examined for methane/air and hydrogen/nitrogen/air mixtures over the entire range of mixture concentrations in the interacting flames. Results show that these flammable limits can be significantly modified in the presence of interaction such that mixture conditions beyond the flammability limit can be still burn if it is supported by stronger flame. The experiment also discusses various oscillatory instabilities in a stability map.

• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.204-210
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• 1998

A method is developed to include the effect of volume expansion in the description of the flame dynamics using G-equation. Line volume-source is used to represent the effect of the exothermic process of combustion with source strength determined by the density difference between the burned and the unburned region. Volume expansion adjusts the flow field to accommodate the increased volume flow rate crossing the flame front. Test result predicted the measured velocity field qualitatively. The method was applied to study the interaction of vortex and premixed flame. Increased volume expansion did not change the initial growth rate of flame area. However, the residence time and flame surface area increased with higher expansion ratios.