• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.6
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• pp.768-773
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• 2014

In this study, experimental and numerical studies for the synthesis of carbon nanotube(CNT) in methane counterflow diffusion flame have been performed. Methane mixed with acetylene($C_2H_2$) was used as a fuel gas and ferrocene was used as a catalyst for synthesis of CNT. The major parameters was $C_2H_2$ mixing rate and mixing rates were 2 %, 6 %, and 10 %. Characteristics of CNT formation on grid were analyzed from SEM images. the chemical reaction mechanism adopted is GRI-MECH 3.0. Numerical results showed that flame temperature and CO mole fraction were increased with increasing acetylene mixing rate. Experimental results showed that the CNT synthesis in 2% acetylene mixture flame better than that of 6% and 10% acetylene mixture flames. It can be considered that 6% and 10% acetylene mixture flames generated the excessive carbon source and then it interrupted the supplement of the carbon source into ferrocene catalyst. It can be found that the supply of appropriate quantity of carbon source can make effect to synthesis of high purity of CNT.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.857-864
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• 2012

A linear stability analysis of a diffusion flame with radiation heat loss is performed to identify linearly unstable conditions for the Damk$\ddot{o}$hler number and radiation intensity. We adopt a counterflow diffusion flame with unity Lewis number as a model. Near the kinetic limit extinction regime, the growth rates of disturbances always have real eigenvalues, and a neutral stability condition perfectly falls into the quasi-steady extinction. However, near the radiative limit extinction regime, the eigenvalues are complex, which implies pulsating instability. A stable limit cycle occurs when the temperatures of the pulsating flame exceed the maximum temperature of the steady-state flame with real positive eigenvalues. If the instantaneous temperature of the pulsating flame is below the maximum temperature, the flame cannot recover and goes to extinction. The neutral stability curve of the radiation-induced instability is plotted over a broad range of radiation intensities.

• Journal of the Korean Society of Combustion
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• v.18 no.4
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• pp.29-36
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• 2013

Numerical study was conducted to clarify effects of added $CO_2$ for the downstream interaction between $H_2$-air and CO-air premixed flames in counterflow configuration. The reaction mechanism adopted was Davis model which had been known to be well in agreement with reliable experimental data. The results showed that both lean and rich flammable limits were reduced. The most discernible difference between the two with and without having $CO_2$ addition into $H_2$-air and CO-air premixtures was two flammable islands for the former and one island for the latter at high strain flame conditions. Even a small amount of $H_2$, in which $H_2$-air premixed flame cannot be sustained by itself, participates in CO oxidation, thereby altering the CO-oxidation reaction path from the main reaction route $CO+O_2{\rightarrow}CO_2+O$ with a very long chemical time in CO-air flame to the (H, O, OH)-related reaction routes including $CO+OH{\rightarrow}CO_2+H$ with relatively short chemical times. This intrinsic nature alters flame stability maps appreciably. The results also showed that chemical effects of added $CO_2$ suppressed flame stabilization. Particularly this phenomenon was appreciable at flame conditions which lean and rich extinction boundary was merged. The detailed discussion of chemical effects of added $CO_2$ was addressed to the present downstream interaction.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.275-278
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• 2006

Systematic experiments in $CH_4/Air$ counterflow diffusion flames diluted with He have been undertaken to study the oscillatory instability in which lateral heat loss could be remarkable at low global strain rate. The oscillatory instability arises for Lewis numbers greater than unity and occurs near extinction condition. The dynamic behaviors of extinction in this configuration can be classified into three modes; growing, harmonic and decaying oscillation mode near extinction. As the global strain rate decreases, the amplitude of the oscillation becomes larger. This is caused by the increase of lateral heat loss which ran be confirmed by the reduction of lateral flame size. Oscillatory edge flame instabilities at low global strain rate are shown to be closely associated with not only Lewis number but also heat loss (radiation and lateral heat loss).

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.4 s.247
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• pp.343-349
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• 2006

Systematic experiments in $CH_4/Air$ counterflow diffusion flames diluted with He have been undertaken to study the oscillatory instability in which lateral flame size was less than burner nozzle diameter and thus lateral heat loss could be remarkable at low global strain rate. The oscillatory instability arises for Lewis numbers greater than unity and occurs near extinction condition. The oscillation is the direct outcome from the advancing and retreating edge flame. The dynamic behaviors of extinction in this configuration can be classified into three modes; growing, harmonic and decaying oscillation mode near extinction. As the global strain rate decreases, the amplitude of the oscillation becomes larger. This is caused by the increase of lateral heat loss which can be confirmed by the reduction of lateral flame size. Oscillatory edge flame instabilities at low global strain rate are shown to be closely associated with not only Lewis number but also heat loss (radiation and lateral heat loss).

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.4
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• pp.356-362
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• 2023

The risk of climate change has been long acknowledged, and ongoing efforts to overcome this issue, within the shipping sector, with the international maritime organization playing a central role. Conducting research on characteristics of soot formation is crucial to control its occurrence within the combustion process. In this study, the laser extinction method and chemical reaction numerical analysis were employed to examine the alterations in the state of chemical species associated with flame temperature, flame visual, and soot formation by mixing nitrogen, an inert gas, in the counterflow diffusion flame based on ethylene gas. The findings of the study suggest that as the mixing ratio of nitrogen increased, both the flame temperature and soot volume fraction decreased. Additionally, the area in which soot particles were distributed also decreased, and the volume fraction decrease rate declined when the mixing ratio increased by more than 30%. The mole fraction of the chemical species involved in soot growth also decreased. the chemical species associated with the HACA reaction were affected by variations in the hydrocarbon fuel ratio, and the chemical species related to the odd carbon path were confirmed to be affected by the flame temperature as well as the hydrocarbon fuel ratio.