• 한국연소학회:학술대회논문집
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• 2001.06a
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• pp.31-45
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• 2001

The effect of adding carbon dioxide to methane-air flame was investigated experimentally. Measurements included extinction limits, flame temperature and photographic investigation of flame. A diffusion flame was stabilized between counterflowing streams of methane diluted with carbon dioxide and air diluted with carbon dioxide. Extinction limits and temperature for such flames were measured over a wide parametric range and were compared with those for other flames that fuel or oxidant was diluted with nitrogen or argon. The experimental results indicate that extinction phenomena can be explained by thermal effect and as an amount of carbon dioxide in fuel or oxidant increases, greatly as compared with other flames flame-temperature falls and flame-thickness is reduced.

• Journal of the Korean Society of Combustion
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• v.13 no.4
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• pp.26-36
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• 2008

Experimental study is conducted to identify the existence of a shrinking flame disk and to clarify its flame characteristics through the inspection of critical mole fraction at flame extinction and edge flame oscillation at low strain rate flames. Experiments are made as varying global strain rate, velocity ratio, and burner distance. The transition from a shrinking flame disk to a flame hole is verified through gradient measurements of maximum flame temperature. The evidence of edge flame oscillation in flame disk is also provided through numerical simulation in microgravity. It is found at low strain rate flame disks in normal gravity that buoyancy effects are importantly contributing to lateral heat loss to burner rim, and is proven through critical mole fraction at flame extinction, edge flame oscillation, and measurements of flame temperature gradient along flame disk surface.

• Fire Science and Engineering
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• v.26 no.4
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• pp.55-62
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• 2012

The suppression mechanisms of carbon dioxide ($CO_2$) as a representative fire suppression agent were revisited using a counterflow diffusion flame which could be applied the concept of a local application system. To end this, the low strain rate $CH_4$/air counterflow diffusions with $CO_2$ addition in either fuel or oxidizer stream were examined numerically using detailed-kinetic chemistry. Radiative heat loss due to radiating gas species including $CO_2$ added was considered by the optically thin model (OTM). As a result, the critical $CO_2$ volume fractions in the oxidizer stream required to extinguish the flame were in good agreement with the experimental data reported in the literature, while somewhat under-prediction was observed with $CO_2$ added in the fuel stream. The surrogate agents were adopted to estimate the quantitative contribution with changing in global strain rate ($a_g$) on the flame extinguishment among pure dilution effect, thermal effects including radiation heat loss and chemical effect due to the $CO_2$ fire suppression agent.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.9 s.252
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• pp.905-912
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• 2006

Experiments in low strain rate methane-air counterflow diffusion flames diluted with $CO_2$ have been conducted to investigate the flame extinction behavior and edge flame oscillation in which flame length is less than the burner diameter and thus lateral conductive heat loss in addition to radiative loss could be remarkable at low global strain rates. The critical mole fraction at flame extinction is examined in terms of velocity ratio and global strain rate. It is seen that flame length is closely relevant to lateral heat loss, and this sheets flame extinction and edge flame oscillation considerably. Lateral heat loss causes flame oscillation even at fuel Lewis number less than unity. Edge flame oscillations are categorized into three: a growing-, a harmonic- and a decaying-oscillation mode. Onset conditions of the edge flame oscillation and the relevant modes are examined with global strain rate and $CO_2$ mole fraction in fuel stream. A flame stability map based on the flame oscillation modes is also provided at low strain rate flames.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.1
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• pp.29-35
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• 2001

Radiation-induced oscillatory instability in CH$_4$/Air diffusion flames is numerically investigated by adopting detailed chemistry. Counterflow diffusion flame is employed as a model flamelet and optically thin gas-phase radiation is assumed. Attention is focused on the extinction regime induced by radiative heat loss, which occurs at low strain rate. Once a steady flame structure is obtained for a prescribed value of initial strain rate, transient solution of the flame is calculated after a finite amount of strain-rate perturbation is imposed on the steady flame. Depending on the initial strain rate and the amount of perturbed strain rate, transient evolution of the flame exhibits various types of flame-evolution behaviors. Basically, the dynamic behaviors can be classified into two types, namely oscillatory decaying solution and diverging solution leading to extinction.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.2
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• pp.232-240
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• 1986

Extinction characteristics of the two interacting premixed flames are analyzed for the effects of flame stretch and preferential diffusion using large activation energy asymptotic analysis by adopting counterflow system as a model problem. Results show that the flammable limit of the thermally interacting premixed flames is extended compared to the single flame, and the extinction mechanism is classified into weak and strong interactions. As the lewis number of the deficient species increases, the region of strong interaction diminishes which can explain the different characteristics of the extinction boundaries of the lean (rich) methane/air and butane/air flames. The influence of the flame stretch to the interaction boundaries is also studied.

• Journal of the Korean Society of Combustion
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• v.21 no.1
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• pp.38-45
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• 2016

Flame characteristics and NO emission behavior in $CH_4$/air-air premixed counterflow flames with applying FIR and FGR with $CO_2$ and $H_2O$ were investigated numerically by varying the ratios of FIR and FGR as well as global strain rate. Chemical effects of added $CO_2$ and $H_2O$ via FIR and FGR were analyzed through comparing flame characteristics and NO behaviors from real species($CO_2$ and $H_2O$) with those from their artificial species($XCO_2$ and $XH_2O$) which have the same thermochemical, radiative, and transport properties to those for the real species. The results showed that flame temperature and NO emission with FIR varied much more sensitively than that with FGR. Those varied little irrespective of adding $CO_2$, $H_2O$, and their artificial species to the fuel stream via FIR. However, Those were varied complicatedly by chemical effects of added $CO_2$ and $H_2O$ via FGR. Detailed analyses for them were made and discussed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.279-282
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• 2006

Experiments in low strain rate methane-air counterflow diffusion flames diluted with $CO_2$ have been conducted to investigate the flame extinction behavior and edge flame oscillation The critical mole fraction at flame extinction is examined in terms of velocity ratio and global strain rate. Onset conditions of the edge flame oscillation and the relevant modes are also provided with global strain rate. It is observed that flame length is intimately relevant to lateral heat loss, and this affects flame extinction and edge flame oscillation considerably. Edge flame oscillations are categorized into three: a growing-, a decaying-, and a harmonic-oscillation mode.

• Journal of the Korean Society of Combustion
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• v.6 no.2
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• pp.15-22
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• 2001

A pressure-based, unstructured finite volume method has been applied to couple the chemical kinetics and fluid dynamics and to capture effectively and accurately the steep gradient flame field. The pressure-velocity coupling is handled by two methodologies including the pressure-correction algorithm and the projection scheme. A stiff, operator-split projection scheme for the detailed nonequilibrium chemistry has been employed to treat the stiff reaction source terms. The conservative form of the governing equations are integrated over a cell-centered control volume with collocated storage for all transport variables. Computations using detailed chemistry and variable transport properties were performed for two laminar reacting flows: a counterflow hydrogen-air diffusion flame and a lifted methane-air triple flame. Numerical results favorably agree with measurements in terms of the detailed flame structure.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.325-328
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• 2012

Radiation effects on the partially premixed methane flames diluted with water vapor in the air stream were numerically investigated. OPPDIF code and GRI-v3.0 were used in the numerical simulation. Adiabatic condition was compared with two different radiation models, optically-thin and WSGGM models. It was found that the radiation effect on the flame structure for the equivalence ratio (${\Phi}$) of 2.5 was less than ${\Phi}=1.5$. Extinction limit was not affected significantly, however, local flame structure was markedly influenced by the radiation models as increasing the water vapor concentration.