• 한국연소학회:학술대회논문집
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• 2001.11a
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• pp.42-50
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• 2001

An experimental study has been carried on high-preheated temperature air combustion. Because the flames with high-preheated temperature air combustion were much more stable and homogeneous(both temporally and spatially) as compared to the room-temperature combustion air. The global flame feature showed range of flame colors (yellow, blue, blurish-green) over the range of conditions. Low level of NOx along with low level of CO have been obtained under high-preheated air combustion conditions. The thermal and chemical behavior of high-preheated air combustion flames depends on preheated temperature and oxygen concentration air.

• Journal of the Korean Society of Combustion
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• v.15 no.4
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• pp.1-8
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• 2010

Mild combustion is considered as a promising combustion technology for energy saving and low emission of combustion product gases. In this paper, the controllability of reaction region in mild combustion is examined by using co-axial air nozzle. For this purpose, numerical approach is carried out. Propane is considered for fuel and air is considered for oxidizer and the temperature of air is assumed 900K slightly higher than auto ignition temperature of propane. But unlike main air, the atmospheric condition of co-axial air is considered. Various cases are conducted to verify the characteristics of Co-Axial air burner configuration. The use of coaxial air can affect reaction region. These modification help the mixing between fuel and oxidizer. Then, reaction region is reduced compare to normal burner configuration. The enhancement of main air momentum also affects on temperature uniformity and reaction region. The eddy dissipation concept turbulence/chemistry interaction model is used with two step of global chemical reaction model.

• 한국연소학회:학술대회논문집
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• 2001.11a
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• pp.51-56
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• 2001

An experiment using preheated air in the coaxial diffusion flame burner was carried out in order to decrease NOx emission and improve the thermal efficiency. Preheated air combustion generally produces high NOx emissions but it was known very well to reduce NOx emission by diluting the combustion air with inert gas in preheated air combustion. In our study, $N_2$ gas was used for diluent and propane was utilized for fuel. We set the combustion air temperature on 300K, 500K, 700K, 900K and dilution level from 21% to 10% in terms of oxygen concentration. NOx emission increased along increment of combustion air temperature and decreased along increment of dilution level(lowering of oxygen concentration in combustion air). Flame-off limit with dilution level enhanced, flame length became longer and the location of maximum flame temperature became lower with increasing of combustion air temperature.

• Journal of the Korean Society of Combustion
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• v.7 no.3
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• pp.1-8
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• 2002

An experimental study has been carried on high-preheated temperature air combustion. The flames with high-preheated temperature air combustion turned out to be both temporally and spatially much more stable and homogeneous than these with room-temperature combustion air. The global flame feature showed a range of flame colors (yellow, blue, blurish-green) according to the flame conditions. A low level of NOx along with low level of CO has been obtained under high-preheated air combustion conditions. The thermal and chemical behavior of high-preheated air combustion flames depends on the preheated temperature and the oxygen concentration of air.

• Journal of the Korean Society of Combustion
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• v.12 no.1
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• pp.28-37
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• 2007

Numerical study is conducted to grasp the flame structure and NO emissions for a wide range of oxy-fuel combustion (covering from air blown combustion to pure oxygen combustion) and for various mole fractions of recirculated $CO_2$ in $CH4-O_2/N_2/CO_2$ counterflow diffusion flames. Special concern is given to the difference of the flame structure and NO emissions between air blown combustion and oxy-fuel combustion w/o recirculated $CO_2$ and is also focused on chemical effects of recirculated $CO_2$. Air blown combustion and oxy-fuel combustion w/o recirculated $CO_2$ are shown to be considerably different in the flame structure and NO emissions. Modified fuel oxidation reaction pathways in oxygen-enriched combustion are provided in detail compared to those in air blown combustion w/o recirculated $CO_2$. The formation and destruction of NO through Fenimore and thermal mechanisms are also compared for air blown combustion and oxyegn-enriched combustion w/o recirculated $CO_2$, and the role of the recirculated $CO_2$ and its chemical effects are discussed. Importantly contributing reaction steps to the formation and destruction of NO are also estimated in oxygen-enriched combustion in comparison to air blown combustion.

• 한국연소학회:학술대회논문집
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• 1999.10a
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• pp.149-154
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• 1999

The influences of air staging on NOx emission and burnout of coal flames were investigated using 1MWth combustion test facility. The experiments showed that variation of overall excess air ratio led to a relatively higher NOx emission level for ${\lambda}=1.2.$ When air staging was applied to the combustion air, it was confirmed that a fuel rich primary combustion zone was established and unburned char was burened completely by mixing with the staged air supplied radially around the flame. The NOx emissions were redued by increasing the staged air flow rate, and staging air was suggested to be more than 40% of the total combustion air for the substantial NOx reduction.

• 한국연소학회:학술대회논문집
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• 2003.12a
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• pp.89-94
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• 2003

For the development of high efficiency and low emission combustion systems, high temperature air combustion technology has been tested by utilizing preheated air over 1100 K and exhaust gas recirculation. In this system, combustion air is diluted with large amount of exhaust gases ($N_2$, $CO_2$), such that the oxygen concentration is relatively low in the reaction zone, leading to low flame temperature. Since, the temperature fluctuations and sound emissions form the flame are small and flame luminosity is low, the combustion mode is expected to be flameless or mild combustion. Experiment was performed to investigate the turbulent flame structure and $NO_X$ emission characteristics in the high temperature air combustion focused on coflowing jet diffusion flames which has a fundamental structure of many practical combustion systems. The effect of turbulence has also been evaluated by installing perforated plate in the oxidizer inlet nozzle. LPG was used as a fuel. Results showed that even though $NO_X$ emission is sensitive to the combustion air temperature, the present high temperature air combustion system produce low $NO_X$ emission because it is operated in low oxygen concentration condition in excess of dilution.

• Journal of Mechanical Science and Technology
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• v.14 no.4
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• pp.433-440
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• 2000

The influence of combustion air at temperatures on nitric oxide emission was studied. The nitric oxide emission generally increases with a rise in the temperature of the combustion air. However, if combustion products for dilution of fuel or combustion air are used before the combustion reaction, then the nitric oxide emission can be reduced even when highly preheated air for combustion air is used. Combustion in low oxygen concentrations flattens the firing mode, resulting in a uniform reaction, and, thus, low nitric oxide emission can be achieved.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.3
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• pp.359-364
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• 2004

For the development of high efficiency and low emission combustion systems, high temperature air combustion technology has been tested by utilizing preheated air over 1100 K and exhaust gas recirculation. In this system, combustion air is diluted with large amount of recirculated exhaust gases, such that the oxygen concentration is relatively low in the reaction zone, leading to low flame temperature. Since, the temperature fluctuations and sound emissions from the flame are small and flame luminosity is low, the combustion mode is expected to be flameless or mild combustion. Experiment was performed to investigate the turbulent flame structure and NO$_x$ emission characteristics in the high temperature air combustion focused on coflowing jet diffusion flames which has a fundamental structure of many practical combustion systems. The effect of turbulence has also been evaluated by installing perforated plate in the oxidizer inlet nozzle. LPG was used as a fuel. Results showed that even though NO$_x$ emission is sensitive to the combustion air temperature, the present high temperature air combustion system produce low NO$_x$ emission because it is operated in low oxygen concentration condition by the high exhaust gas recirculation.

• Journal of the Korean Society of Combustion
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• v.3 no.1
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• pp.49-57
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• 1998

High temperature preheated and diluted air combustion has been developed as the technology to realize higher thermal efficiency. In this type of combustion, there are many interesting phenomena which cannot be observed in room temperature air combustion. The characteristics of the combustion, investigated using a 3500 kcal/h LPG fired test facility, are described. The flame is demonstrated to have a blue and green in color and has a large volume. As the preheated air temperature increased up to $1000\;^{\circ}C$, the NOx emission incrased exponentially over a few hundred ppm with 11% $O_2$ correction. But, it drastically reducedabout 20ppm when the air was diluted from 21% $O_2$ to 5% $O_2$.