• 한국연소학회:학술대회논문집
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• 2000.05a
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• pp.57-66
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• 2000

OH radical and NO distributions have been measured in methane/air partially premixed counterflow flames(${\alpha}$=1.0, 0.8, 0.6) using PLIF technique. The results are discussed and compared with the numerical analysis results obtained under the same flame conditions. Measured OH and NO LIF signals agree with the computed concentration distributions. Both numerical and experimental results indicate that the structural change in a flame alters the NO formation characteristics of a partially premixed counterflow flame. The nitrogen dilution also changes flame structure, temperature and OH radical distributions and results in the decreased NO concentrations in a flame. The levels of decrease in NO concentrations, however, depends on the premixedness(${\alpha}$) of a flame. The larger change in the flame structure and NO concentrations have been observed in a premixed flame($\alpha$=1.0), which implies that the premixedness is likely to be a factor in the dilution effect on NO formation of a flame.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.2
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• pp.170-177
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• 2005

The fuel-lean premixed flame has been considered one of the most efficient ways to reduce $NO_X$ emission during a combustion process. However, it is difficult to achieve stable fuel-lean premixed flames over the wide range of equivalence ratios: therefore, the application of fuel-lean flames to a practical combustion system is rather limited. In this study, the stability characteristics of fuel-lean flames stabilized by fuel-rich flames are investigated experimentally using a slot burner as a part of the basic research for practical application such as lean burn engines. Spontaneous emission of radical species were examined to understand the stability mechanisms of rich-lean premixed flames. The presence of fuel-rich flames could significantly lower the lean limit of fuel-lean flames. The stability of a fuel-lean flame is enhanced with the increase of fuel flow rate in a fuel-rich flame; how ever, it is not sensitive to the equivalence ratio of fuel-rich flames in the range of 1.2-2.4. The mechanisms of stable rich-lean premixed flames could be understood based on the characteristics of triple flame.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.6
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• pp.991-1000
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• 1987

Existence of triple flames in a lean-rich concentration field is studied both experimentally and theoretically using large activation energy asymptotic technique adopting counterflow system as a model problem. Experiment shows that in triplet system of a lean and a rich premixed flame separated by a diffusion flame, either lean or rich premixed flame merges with diffusion flame as stretch is increased, such that transition boundary between 3-flame and 2-flame exists. The region in which 3-flame can exist forms an island within rich-lean concentration fields for large stretch, where as it is extends to the line of (.OMEGA.$_{0}$/.OMEGA.$_{F}$)$_{R}$=0 or (.OMEGA.$_{F/}$.OMEGA.$_{0}$)$_{L}$=0 for small stretch. Theoretical results show the qualitative agreement with experiment and the existence of limiting stretch over which 3-flame can not exist.t.t.t.t.t.t.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.1
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• pp.7-14
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• 2008

It has been reported that partially premixed interacting flame could be sustained till sonic exit velocities if eight small nozzles are arranged optimally and one nozzle on the center is fed small amount of fuel. But the equivalence ratios in this experiments were 20-60. In this research, experiments were conducted to know the effects of lean-rich staging in multiple jet flames on the blowout velocity. The fuel mole tractions in the fuel-air mixture, the nozzle exit velocity and the diameter between adjacent nozzles were alternatively changed. When the lower mole fraction fuel was fed to the nozzles located near the center and small amount of fuel to the center nozzle, flame was not extinguished even at the nozzle exit velocity of 200m/s. Also the interacting flame could be sustained till that velocity when four small size nozzles for lean mixture were located within the arrangement of four nozzles for rich mixture and configured optimally.

• 한국연소학회:학술대회논문집
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• 2002.11a
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• pp.19-24
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• 2002

Recent studies of a triple flame suggested that the presence of triple point (triple line in this planar configuration) could explain the mechanisms of stable fuel-lean premixed flames with equivalence ratio lower than the flammability limit. In the present study, for better understanding of the stability mechanisms of fuel rich-lean premixed flames, the fuel-rich flames were replaced with hot coils that will provide heat flux into the fuel-lean flames. It is found that the fuel-lean premixed flames could be stabilized without any triple point (triple line): however, the equivalence ratio limit for stable fuel-lean flame in this case is higher than that of the present work with the presence of fuel-rich flames. These results demonstrate that heat flux coming from fuel-rich flames should be considered in order to properly understand the roll of a triple flame for stable fuel rich-lean flames.

• 한국연소학회:학술대회논문집
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• 2006.04a
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• pp.55-62
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• 2006

A two-step fuel-rich/fuel-lean catalytic combustion seems to be one of the most effective methods to control simultaneously the NO generation and the hydrocarbon (HC) conversion from fuel-bound nitrogen. By controlling equivalent air ratio for maintaining fuel-rich and fuel-lean condition over each catalytic layer, space velocity, inlet temperature, and catalyst component, the HCand ammonia conversion efficiency higher than 95% could be achieved, with ammonia conversion to NO remaining below 5%. The experimental results wouldbe applied to the combustion of land fill gas and to gasified refuse-derived fuels as a method of minimizing NO generation.

• Journal of the Korean Society of Combustion
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• v.18 no.3
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• pp.68-74
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• 2013

가스터빈용 희박 예혼합 연소기 내부에 와류 발생기(vortex generator)를 장착하여 그에 따른 연료/공기혼합 및 NOx 배출 특성 변화를 조사하였다. 이를 위해 수치해석적 방법을 채택하여 연소기내 유동특성, 연료/공기 혼합도, 배기가스(NOx), 화염형상을 분석하였다. 와류 발생기를 장착한 경우, 연소기 내부에서 와류 발생기에 의한 나사산 형상으로 인해 와류가 형성되며 이는 연소기 전면부까지 유지되었다. 또한 연소기 내부 면적 차로 인해 압력섭동이 발생하였다. 이와 더불어 연소기 전면부 기준 상류지역의 연료와 공기의 혼합도가 증가됨으로서 연료 과농지역이 감소하게 되며 이로 인해 전반적인 NOx 발생량의 감소 효과를 볼 수 있었다. 화염 형상의 변화로부터 와류 발생기의 영향으로 선회수는 다소 감소할 것으로 예상되며, 이는 와류 발생기로 인한 유속의 반복적 증감에 의한 결과라고 판단된다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.1
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• pp.377-383
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• 1996

Interaction of flames in a lean-rich concentration field is studied numerically adopting a counterflow as a model problem. Detailed kinetic mechanism is adopted in analyzing the structure of various type of flames which can be found in lean-rich interaction. Flow field is simplified to quasi one-dimensional by using boundary layer approximation and similarity formulation. Triple flames are identified and its structure shows that a diffusion flame is located in the middle of two premixed flames. Such a diffusion flame is formed by $H_2$ and CO generated from the rich premixed flame and $O_2$ leaked from the lean premixed flame. The flame position can be identified either from the hydrogen production rate or the heat release rate. Transition from single diffusion flame to triple flame is observed as degree of premixing is increased.

• Applied Chemistry for Engineering
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• v.7 no.4
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• pp.661-669
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• 1996

Pt-Rh/NaY catalysts with various Pt/Rh ratios were prepared by an ion-exchange method and their characteristics were investigated by $^{129}Xe$-NMR and EXAFS. Both the $^{129}Xe$-NMR and EXAFS data indicate that the surface of PtRh bimetallic clusters was enriched with Rh atoms. The catalytic activities of these catalysts for conversion of CO, HC and $NO_x$ were measured by using simulated automobile engine exhausts under lean, rich and stoichiometric conditions. The Pt-Rh/NaY(Pt/Rh=1) catalyst exhibited the greatest reactive activity among the catalysts used in this study.

• Journal of the Korean Society of Combustion
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• v.20 no.2
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• pp.28-35
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• 2015

In this study, the CH4/air lean-rich combustion system with exhaust gas recirculation (EGR) was investigated to explore the potential for lowering pollutant emissions. To achieve this purpose, experiments of lean-rich combustion system with EGR were conducted to measure the changes in the characteristics of the pollutant emission and flame shape with various equivalence ratios and EGR rates. Here, this study was applied to the fuel distribution ratio of 3:1 for the formation of the lean and rich flames. Additionally, the results were compared with $CH_4$/air lean premixed combustion system. The results show that flame shape of lean-rich combustion system was determined by lean and rich equivalence ratios (${\Phi}_L$ and ${\Phi}_R$) and stratified flame was formed with increasing ${\Phi}_R$. According to the pollutant emission characteristics based on experimental results, the NOx and CO emission index (EINOx and EICO) decreased with increasing EGR rate. Especially, in the range needed to form a stable flame, the reduction rates of EINOx and EICO were approximately 47% and 48% for an EGR rate of 25%, global equivalence ratio of 0.85 and ${\Phi}_L$ of 0.80 compared with lean premixed combustion system (${\Phi}$ = 0.78).