• Journal of Mechanical Science and Technology
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• 제19권6호
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• pp.1358-1365
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• 2005

Flue gas recirculation (FGR) is widely adopted to control NO emission in combustion systems. Recirculated flue gas decreases flame temperature and reaction rate, resulting in the decrease in thermal NO production. Recently, it has been demonstrated that the recirculated flue gas in fuel stream, that is, the fuel induced recirculation (FIR), could enhance much improved reduction in NO per unit mass of recirculated gas, as compared to conventional FGR in air. In the present study, the effect of dilution methods in air and fuel sides on NO reduction has been investigated numerically by using $N_2$ and $CO_2$ as diluent gases to simulate flue gases. Counterflow diffusion flames were studied in conjunction with the laminar flamelet model of turbulent flames. Results showed that $CO_2$ dilution was more effective in NO reduction because of large temperature drop due to the larger specific heat of $CO_2$ compared to $N_2$. Fuel dilution was more effective in reducing NO emission than air dilution when the same recirculation ratio of dilution gas was used by the increase in the nozzle exit velocity, thereby the stretch rate, with dilution gas added to fuel side.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2003년도 추계학술대회 논문집
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• pp.115-120
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• 2003

Flow characteristics at secondary recirculation zone in a liquid fuel ramjet combustor are investigated using CFD and 3-D Stereoscopic PIV method. The combustors have two rectangular inlets that form 90 degree each other. Three guide vanes were installed in each rectangular inlet to improve the flow stability. The tested angle of the air intakes was 60 degree. The experiments were performed in the water tunnel test with the same Reynolds number in the case of Mach0.3 at inlet. Both computational and experimental results showed the secondary recirculation flow occurred at the front junction of inlet main stream and combustor chamber. The size of secondary recirculation region increased with upon closer center of axial combustor. Since the performance of combustor depends on not only the main recirculation in the dome region but also the secondary recirculation flow in a junction region, the optimal angle of the air intakes should consider the recirculation size as frame holder.

• 한국대기환경학회지
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• 제23권3호
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• pp.297-310
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• 2007

Recent evidence has demonstrated that the pollutant recirculation can play an important role in leading to high ozone $(O_3)$ concentrations. In this study, the MM5-CAMx air quality modeling system was applied to simulate the pollutant recirculation and identify the transport of pollution during the high $O_3$ event (the maximum $O_3$ of 195 ppb) observed in the Greater Seoul Area (GSA) on $1{\sim}4$ June in 2004. The results showed a weak northeasterly synoptic wind during the night and early morning moved the air parcels containing the locally emitted urban pollution to the coast, which contributed to enhance $O_3$ formation in the southwest part of the GSA. As the sea breeze developed and started to penetrate inland in the late afternoon, the rapid build-up of $O_3$ concentration was found in the southwest coastal area due to the recirculation of the polluted air loaded with high level $O_3$. The simulated backward trajectories and observations at coastal sites confirmed the recirculation of pollutant with the late sea breeze is the dominant factor affecting the occurrence of high $O_3$ concentrations in the southwestern GSA.

• 한국가스학회지
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• 제23권3호
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• pp.1-6
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• 2019

본 연구는 폐기물 소각로에서 질소산화물 저감을 위해 고온의 배기가스를 연소로에서 재순환하여 연소용 공기와 혼합하여 배기가스 재순환을 이용한 방법에서 고온의 배기가스를 별도의 동력 팬이 없이 코안다 노즐을 이용한 배기가스 재순환 장치에 관한 연구이다. 코안다 노즐에서 공기 공급 노즐 간극의 변화와 공기 공급 노즐의 위치에 따른 배기가스 재순환 유량 특성과 혼합 가스의 출구에서 평균온도 변화를 살펴보았다. 공기 공급 노즐의 간극이 3.22, 4.03, 4.84 mm로 변할 때 가장 좁은 3.22 mm일 때가 배기가스 재순환 유량과 공기 공급 유량의 비인 배기가스 재순환 유량비가 2.227로 가장 재순환 유량이 크게 나타났고 혼합가스 평균 온도는 $594.8^{\circ}C$로 나타났다. 공기 공급 노즐의 위치가 코안다 노즐 목의 전방 위치, 목 위치, 확관 위치로 변할 때를 살펴보았으며 전방 위치와 목 위치일 때는 재순환 유량비가 1.843으로 거의 같은 값이고 확관 위치에서는 1.696으로 나타났으며 평균 온도는 $559.8^{\circ}C$와 $544.3^{\circ}C$로 나타났다.

• Journal of Mechanical Science and Technology
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• 제18권12호
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• pp.2303-2309
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• 2004

Flue gas recirculation (FGR) is a method widely adopted to control NOx in combustion system. The recirculated flue gas decreases flame temperature and reaction rate, resulting in the decrease in thermal NO production. Recently, it has been demonstrated that the recirculated flue gas in fuel stream, that is, the fuel induced recirculation (FIR), could enhance a much improved reduction in NOx per unit mass of recirculated gas, as compared to the conventional FGR in air. In the present study, the effect of FGR/FIR methods on NOx reduction in turbulent swirl flames by using N$_2$ and CO$_2$ as diluent gases to simulate flue gases. Results show that CO$_2$ dilution is more effective in NO reduction because of large temperature drop due to the larger specific heat of CO$_2$ compared to N$_2$ and FIR is more effective to reduce NO emission than FGR when the same recirculation ratio of dilution gas is used.

• 한국가시화정보학회지
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• 제3권1호
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• pp.58-62
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• 2005

Flow characteristics at secondary recirculation zone in a liquid fuel ramjet combustor were investigated using CFD and Stereoscopic PIV method. The combustors have two rectangular inlets that form 90 degree each other. Three guide vanes were installed in each rectangular inlet to improve the flow stability. The tested angle of the air intakes was 60 degree. The experiments were performed in the water tunnel test with the same Reynolds number in the case of Mach 0.3 at inlet. The computational and experimental results showed that the secondary recirculation flow occurred at the front junction of inlet main stream and combustor chamber. The size of secondary recirculation regions are increased with approaching closer to the center of the combustor. Since the performance of combustor is closely dependent not only on the main recirculation in the dome region but also on the secondary recirculation flow in a junction region, the optimal angle of the air intakes should be considered the recirculation size as frame holder.

• 한국연소학회지
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• 제18권2호
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• pp.8-16
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• 2013

The flameless combustion has been considered as one of the promising combustion technology for high thermal efficiency, reducing NOx and CO emissions. In this paper, the effect of air and fuel injection condition on formation of flameless combustion was analyzed using three dimensional numerical simulation. The results show that the high temperature region and the average temperature was decreased due to increase of recirculation ratio when air velocity is increased. The average temperature was also affected by entrainment length. Generally mixing effect was enhanced at low entrainment length and dilution was dominated at high entrainment length. This entrainment length was greatly affected by air and fuel injection velocity and distance between air and fuel. It is also found that the recirculation ratio and dilution effect were generally increased by entrainment length and the recirculation ratio, mixing and dilution effect are the significant factor for design of flameless combustion system.

• 대한기계학회논문집B
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• 제28권3호
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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.

• 한국연소학회지
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• 제21권1호
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• pp.31-37
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• 2016

Swirler generates the overall swirling flow in the combustion chamber and this swirling flow governs the flame stability and enhances fuel atomization. This paper deals with the flare angle effects on flow streamlines, recirculation zone, Central Toroidal Recirculation Zone(CTRZ) and Corner Recirculation Zone(CRZ) in the model combustion chamber using counter-rotating swirler. 2D PIV system was employed to obtain the velocity components and test condition was obtained using Reynolds Analogy equivalent to air test. We observed transitional flow patterns of flare angle increased. The obtained results show that the flare angle controls the behavior of Recirculation zone, Central Toroidal Recirculation Zone and Corner Recirculation Zone.

• 한국가시화정보학회지
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• 제4권1호
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• pp.56-61
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• 2006

A change of three-dimensional vortical structures on the wake behind a road vehicle has been investigated according to the existence of an air spoiler. To reconstruct the three-dimensional velocity fields, two-dimensional PIV(particle image velocimetry) measurements were performed for lots of the x-y, y-z and z-x planes. Since the isovorticity surface does not represent exactly the vortical structures within the recirculation region due to strong shear flows, the velocity component normal to the x-y plane is obtained by interpolating those velocities in the z-x plane. Then, the ${\lambda}_2-definition$ is applied to visualize the vortices in the recirculation region. As a result, it is found that the air spoiler weakens C-pillar vortices and produces strong wing-tip vortices. Inside the recirculation region, the height and volume of coherent vortices are increased relatively when an air spoiler is equipped. On the other hand, two small coherent vortices are observed in case that an air spoiler is absent.