• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.261-266
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• 2003

An experimental study has been conducted to evaluate the effects of $CO_{2}$ on heat transfer from hydrogen oxygen-enriched flame. Experiments were performed on flames stabilized by a co-flow swirl burner, which mounted on top of the furnace. Five composition conditions of oxidizer were chosen with replacing $N_{2}$ with $CO_{2}$. In a steady state, total and radiative heat flux rates from the flame to the wall of furnace has been measured using heat flux meters. Temperature distribution in furnace also has been checked. Increasing $CO_{2}$ ratio in the oxidizer, the dominant heat transfer mode was changed into convection from radiation. Temperature in the furnace decreased but total heat flux increased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.8 s.227
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• pp.937-944
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• 2004

An experimental study has been conducted to evaluate the effects of $CO_2$ on heat transfer from oxygen-enriched hydrogen flame. Experiments were performed on flames stabilized by a co-flow swirl burner, which was mounted on top of the furnace. Five different oxidizer compositions were prepared by replacing $N_2$ with $CO_2$. In a steady state, the total as well as radiative heat flux from the flame to the wall of furnace have been measured using a heat flux meter. Temperature distribution in furnace also has been measured and compared. By increasing $CO_2$ proportion in the oxidizer, the convection played a more significant role rather than radiation. Overall temperature in the furnace was seen to be decreased, while the total heat flux has increased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.10
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• pp.1458-1464
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• 2002

$CO_2$ is well known greenhouse gas which is the major source of global warming. Reducing $CO_2$ emission in combustion process can be achieved by increasing combustion efficiency, oxygen enriched combustion and recirculation of the emitted $CO_2$ gas. Stability of non-premixed flame in oxygen enriched environment will be affected by the amount of oxygen, kind of diluents and fuel exit velocity. The effects of these parameters on flame liftoff and blowout are studied experimentally oxidizer coflowing burner. Experiments were divided into three cases according as where $CO_2$gas was supplied. - 1) to coflowing air, 2) to fuel with 0$_2$-$N_2$ coflow, 3) to coflowing oxygen. Flame in air coflowing case was lifted in turbulent region. Flame lift and blowout in laminar region with the increase in $CO_2$ volume fraction in $CO_2$-Air mixture makes flame lift and blowout in laminar region. Increase in oxygen volume fraction makes flame stable-i.e. flame liftoff and blowout occur at higher fuel flowrates. Liftoff height was non-linear function of nozzle exit velocity and affected by the $O_2$ volume fraction. It was found that the flame in $O_2$-$N_2$ coflow case was more stable than $O_2$-$CO_2$ case, Liftoff heights vs (nozzle exit velocity/laminar burning velocity)$^{3.8}$ has a good correlation in $O_2$-$CO_2$ oxidizer case.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.12
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• pp.1625-1631
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• 2004

Investigation on Flue Gas Recirculation(FGR) flame and Fuel Injection Recirculation(FIR) flame was performed with numerical method. Quantitative Reaction Path Diagram(QRPD) is utilized to compare the different chemistry effects between FGR flame and FIR flame. In order to compare flamelets in various oxygen-enrichment conditions reasonably, the adiabatic flame temperature and Damkohler number were held fixed by modulating the amount of diluents to fuel and oxidizer stream and by varying global strain rate of flame respectively. Basic flame structures were compared and characteristics of CH$_4$ decomposition and NO formation were analyzed based on QRPD analysis between FGR flame and FIR flame.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.1
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• pp.23-30
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• 2007

The ultimate objective of this study is to develop oxygen-enriched combustion techniques applicable to the system of practical industrial boiler. To this end the combustion characteristics of lab-scale LNG combustor were investigated as a first step using the method of numerical simulation by analyzing the flame characteristics and pollutant emission behaviour as a function of oxygen enrichment level. Several useful conclusions could be drawn based on this study. First of all, the increase of oxygen enrichment level instead of air caused long and thin flame called laminar flame feature. This was in good agreement with experimental results appeared in open literature and explained by the effect of the decrease of turbulent mixing due to the decrease of absolute amount of oxidizer flow rate by the absence of the nitrogen species. Further, as expected, oxygen enrichment increased the flame temperatures to a significant level together with concentrations of $CO_2$ and $H_2O$ species because of the elimination of the heat sink and dilution effects by the presence of $N_2$ inert gas. However, the increased flame temperature with $O_2$ enriched air showed the high possibility of the generation of thermal $NO_x$ if nitrogen species were present. In order to remedy the problem caused by the oxygen-enriched combustion, the appropriate amount of recirculation $CO_2$ gas was desirable to enhance the turbulent mixing and thereby flame stability and further optimum determination of operational conditions were necessary. For example, the adjustment of burner with swirl angle of $30\sim45^{\circ}$ increased the combustion efficiency of LNG fuel and simultaneously dropped the $NO_x$ formation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.8
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• pp.839-845
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• 2011

We performed numerical simulations of freely propagating premixed flames at atmospheric pressure to investigate the influence of trifluoromethane on $CH_4/O_2/N_2$ flames under oxygen enrichment. Trifluoromethane significantly contributed toward a reduction in flame speed, the magnitude of which was larger in terms of the physical effect than the chemical effect. More trifluoromethane could be added and consumed on oxygen-enriched $CH_4/O_2/N_2$ flames. $CHF_3$ was decomposed primarily via $CF_3{\rightarrow}CF_2{\rightarrow}CF{\rightarrow}CF:O{\rightarrow}CO$ and $CHF_3+M{\rightarrow}CF_2+HF+M$ played an important role in oxygen-enhanced flames. When an inhibitor was added to oxygen-enriched flames, the position of the maximum concentration of active radicals was shifted to a relatively low temperature range, and the net rate of OH became higher than that of H.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.115-120
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• 2001

The present study examined the possibility of $NO_{x}$ reduction in the high temperature industrial furnaces. duct burner of gas turbine cogeneration and two-stage gas turbine combustor. The experimental study was carried out for the diffusion flame of second stage combustor with the variations of oxygen concentration and supplying rate of hot exhaust gas from first stage combustor. It also examined the flammability range and $NO_{x}$ formation of the second stage combustor in which the fuel is supplying into the mixture of oxygen hot exhaust gas from first stage combustor. The results show that the enrichment of oxygen and increase of exhaust gas lead to increase the $NO_{x}$ up to 50 ppm with 23% $O_{2}$ condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.8 s.251
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• pp.788-795
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• 2006

From the view of the environmental protection against the use of fossil fuels, the great of efforts have been exerted to find an effective method which is not only pollutant reduction but also high thermal efficiency. Reburning is a useful technology in reducing nitric oxide through injection of a secondary hydrocarbon fuel. In this paper, an experimental study has been conducted to evaluate the hybrid effects of reburning and selective non-catalytic reaction (SNCR) on $NO_x/CO$ reduction from oxygen-enriched LPG flame. Experiments were performed in flames stabilized by a co-flow swirl burner, which was mounted at the bottom of the furnace. Tests were conducted using LPG gas as main fuel and also as reburn fuel. The paper reported data on flue gas emissions, temperature distribution in furnace and various heat fluxes at the wall for a wide range of experimental conditions. Overall temperature in the furnace, heat fluxes to the wall and $NO_x$ generation were observed to increase by oxygen-enriched combustion, but due to its hybrid effects of reburning and SNCR, $NOx/CO$ concentration in the downstream has considerably decreased.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.6
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• pp.647-653
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• 2007

The ultimate objective of this study is to develop a reliable oxygen-enriched combustion techniques especially for the case of the flue gas recycling in order to reduce the $CO_2$ emissions from practical industrial boilers. To this end a systematic numerical investigation has been performed, as a first step, for the resolution of the combusting flame characteristics of lab-scale LNG combustor. One of the important parameters considered in this study is the level of flue gas recycling calculated in oxygen enriched environment. As a summary of flame characteristics, for the condition of 100% pure $O_2$ as oxidizer without any flue gas recycling, the flame appears as long and thin laminar-like shape with relatively high flame temperature. The feature of high peak of flame temperature is explained by the absence of dilution and heat loss effects due to the presence of $N_2$ inert gas. The same reasoning is also applicable to the laminarized thin flame one, which is attributed to the decrease of the turbulent mixing. These results are physically acceptable and consistent and further generally in good agreement with experimental results appeared in open literature. As the level of $CO_2$ recycling increases in the mixture of $O_2/CO_2$, the peak flame temperature moves near the burner region due to the enhanced turbulent mixing by the increased amount of flow rate of oxidizer stream. However, as might be expected, the flue gas temperature decreases due to presence of $CO_2$ gas together with the inherent feature of large specific heat of this gas. If the recycling ratio more than 80%, gas temperatures drop so significantly that a steady combustion flame can no longer sustain within the furnace. However, combustion in the condition of 30% $O_2/70% $ $CO_2$ can produce similar gas temperature profiles to those of conventional combustion in air oxidizer. An indepth analyses have been made for the change of flame characteristics in the aspect of turbulent intensity and heat balance.

• Fire Science and Engineering
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• v.20 no.4 s.64
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• pp.72-76
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• 2006

Polymer/clay nanocomposites have generated considerable interests in the past decade because adding just tiny amount of clay to the polymer matrix could produce a dramatic enhancement in physical, thermal and mechanical properties. Smectite clays, such as montmorillonite (MMT), are of great industrial value because of their high aspect ratio, plate morphology, intercalative capacity, natural abundance and low cost. In this study, PE/MMT nanocomposites were directly prepared by melt intercalating PE and the modified clay. The nanostructure was verified by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and their flame retardant properties were measured and discussed by limiting oxygen index (LOI), char yield and smoke mass concentration. And their thermal stabilities were measured by differential thermogravimetric (DTG) and thermogravimetric analysis (TGA). The PE/MMT nanocomposites proved more effective the conventional composites in reinforcement. Two functions in the thermal stability of the PE/MMT nanocomposite, one is the barrier effect to improve the thermal stability, and another is catalysis, leading to a decrease of the thermal stability. The flammability was greatly decreased due to the formation of the clay-enriched protective char during the combustion.