• 한국연소학회지
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• 제19권3호
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• pp.26-33
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• 2014

We examined the characteristics of $NO_x$ emission for CH4/air non-premixed flames using the exhaust gas recirculation(EGR) methods, which are the air-induced EGR(AI-EGR) and fuel-induced EGR(FI-EGR) methods. Our experimental results show that the $NO_x$ emission index($EI_{NOx}$) decreased with increasing EGR ratio. In the range needed to form a stable flame, the reduction rate of $EI_{NOx}$ for the FI-EGR method was approximately 29% when the EGR ratio was 20%, and the reduction rate for the AI-EGR method was approximately 28% with 25% of the EGR ratio. According to the flame structure based on numerical results, high temperature regions for the FI-EGR method were narrower and lower than those for the AI-EGR method at the same EGR ratio. Furthermore, based on the experimental results for swirl flames, the reduction rate of $EI_{NOx}$ for the FI-EGR method was approximately 49% with 15% of the EGR ratio, while the maximum reduction rate for AI-EGR method was approximately 45% with 25% of the EGR ratio. Consequently, we verified that the FI-EGR method was more effective than the AI-EGR method in reducing $NO_x$ emission for non-premixed flames with EGR. We expect that the results of this study will provide fundamental information relating to hybrid combustion systems, which can be used in the design of combustion systems in the future.

• 대한기계학회논문집B
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• 제28권4호
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• pp.425-432
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• 2004

The objective of this study is a qualitative comparison between line-integrated OH chemiluminescence(OH$\^$*/) image and its Abel inverted image to investigate the flame structure at different phase of the oscillating pressure field. PIV(Particle Image Velocimetry) measurements were conducted under non-reacting conditions to see the global flow structure and NOx emission was measured to investigate the effect of fuel-air premixing on combustion instability and emission characteristics. Experiments were carried out in an atmospheric pressure, laboratory-scale dump combustor operating on natural gas. Combustion instabilities in present study exhibited a longitudinal mode with a dominant frequency of ∼341.8㎐, which corresponded to a quarter wave mode of combustor. Heat release and pressure waves were in-phase when instability occurred. Results gave an insight about the location where the strong coherence of pressure and heat release existed. Also an additional information on active control to suppress the combustion instabilities was obtained. For lean premixed combustion, strong correlation between OH$\^$*/ and NOx emissions was expected largely due to the exponential dependence of thermal NOx mechanism on flame temperature.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제31회 추계학술대회논문집
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• pp.393-396
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• 2008

질소 희석 가스가 수소화염의 화염안정성에 미치는 영향을 실험적으로 연구하였다. 연료는 수소이며 수소화염을 부상시키기 위하여 동축공기를 사용하였다. 이때 수소의 속도는 200 m/s이고 동축공기의 속도는 16 m/s로 고정하였다. 질소 희석 가스는 연료 공급라인에 주입되었으며 전체 연료 부피의 0$\sim$20%까지 주입하였다. 화염구조분석을 위하여 PIV/OH PLIF 동시측정 기법을 사용하였다. 수소 난류 확산화염 화염안정성 실험을 통하여 질소 가스 주입에 따라 부상화염 높이는 증가하였으며, 난류 화염 전파속도는 감소하였다. 그리고 난류 화염전파속도는 난류강도의 함수로 표현될 수 있었다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2007년도 제34회 KOSCO SYMPOSIUM 논문집
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• pp.145-152
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• 2007

The dynamic behaviors of counterflow non-premixed flame have been investigated experimentally to study effects of heat losses on edge flame oscillation, which result from the advancing and retreating edge flame motion of outer flame edge at low strain rate flame. For low strain rate flame, lateral conduction heat loss in addition to radiation heat loss could be more remarkable than the others. Oscillatory instabilities appear at fuel Lewis number greater than unity. But excessive lateral conduction heat loss causes edge flame instability even at fuel Lewis number less than unity. The dramatic change of burner diameters in which flame length is an indicator of lateral conduction heat loss was applied to examine the onset condition of edge flame oscillation and flame oscillation modes. Especially, extinction behaviors quite different from the previous study were observed.

• 한국안전학회지
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• 제27권5호
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• pp.35-41
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• 2012

The Numerical simulation was performed on the flow field around the two-dimensional rectangular bluff body in order to complement the previous experimental results of the bluff body stabilized flames [1]. For both fuel ejection configurations against an oxidizer stream, the flame stability was affected mainly by vortex structure and mixing field near bluff body. FDS(Fire Dynamic Simulator) based on the LES(Large Eddy Simulation) was employed to clarify the isothermal mixing characteristic and wake flow pattern around bluff body. The air used atmosphere and the fuel used methane. The result of counter flow configuration shows that the flow field depends on air velocity but the mixing field is influenced on the fuel velocity. At low fuel velocity the fuel mole fraction is below the flammable limit and hence the mixing is insufficient to react. Therefore, as the result, the flame formed at low fuel velocity is characterized by non-premixed flames. For the flow field of co-flow configuration, flame stability was affected by fuel velocity as well as air velocity. the vortex generated by fuel stream has counter rotating direction against the air stream. Therefore, the momentum ratio between air and fuel stream was important to decide the flame blow out limit, which is result in the characteristic of the partially premixed reacting wake near extinction.

• 한국연소학회지
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• 제12권2호
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• pp.34-41
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• 2007

The dynamic behaviors of counterflow non-premixed flame have been investigated experimentally to study effects of heat losses and Lewis number on edge flame oscillation, which result from the advancing and retreating edge flame motion of outer flame edge at low strain rate flame. For low strain rate flame, lateral conduction heat loss in addition to radiation heat loss could be more remarkable than the others. Oscillatory instabilities appear at fuel Lewis number greater than unity. But excessive lateral conduction heat loss causes edge flame instability even at fuel Lewis number less than unity. The excessive heat loss caused by the smaller burner diameter in which the flame length is an indicator of lateral conduction heat loss extends the region of flame oscillation and accelerates oscillatory instability in comparison to the previous study with the burner diameter of 26mm. Extinction behaviors quite different from the previous study are also addressed.

• 한국연소학회지
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• 제5권1호
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• pp.7-18
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• 2000

Numerical simulations of counterflow non-premixed $CH_4/C_2HCl_3/Air$ flames added 8%(by volume) C2HCl3 on the fuel side are conducted at atmospheric pressure using a detailed chemical reaction mechanism in order to understand the effect of strain rates. A detailed sensitivity analysis is also performed in order to assess the relative influence of each reaction on the flame established at a strain rate of 200s-1. The structure of flames (i.e., temperature, velocity, and concentration of species) established at both a strain rate of 150s-1 and 300s-1 are investigated. As the strain rate increases, the "flame zone" is restricted to a narrower range and the position of maximum temperature is shifted to the fuel side. The concentrations of major species, H2O, CO, H2, HCl, Cl2, and Cl are decreased with increased strain rate. The reaction involving chlorine, CH4 + Cl $\rightarrow$ CH3 + HCl, instead of the reaction, CH4 + H $\rightarrow$ CH3 + H2 influences the consumption of methane. C2HCl3 + OH $\rightarrow$ CHCl2 + CHOCl and HCl + OH $\rightarrow$ H2O + Cl, are major reactions, through which OH radicals are consumed.

• 한국자동차공학회논문집
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• 제15권3호
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• pp.166-173
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• 2007

A numerical study was conducted to have the effect of $CO_2$ addition to fuel on the chemical reaction mechanism with the change of the initial concentration of $CO_2$ and the axial velocity gradient. From this study, it was found that there were two serious effects of $CO_2$ addition on a non-premixed flame ; a diluent effect by the reactive species reduction and chemical effect of the breakdown of $CO_2$ by the third-body collision and thermal dissociation. Especially, the chemical effect was serious at the lower velocity gradient of the axial flow. It was certain that the mole fraction profile of $CO_2$ was deflected and CO was increased with the initial concentration of $CO_2$. It was also ascertained that the breakdown of $CO_2$ would cause the increasing of CO mole fraction at the reaction region. It was also found that the addition of $CO_2$ did not alter the basic skeleton of $H_2-O_2$ reaction mechanism, but contributed to the formation and destruction of hydrocarbon products such as HCO. The conversion of CO was also suppressed and $CO_2$ played a role of a dilution in the reaction zone at the higher axial velocity gradient.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.1013-1018
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• 2008

Vortex Inertial Staged Air (VIStA) burner for an once-through type boiler has been restored to the original premixed type to reduce nitrogen oxide (NOx) emission. The premixed version yields additional de-NOx effect by 20 ppm. The flame is formed closer to the wall at the 1st stage combustion chamber compared with the non-premixed one. The combustion characteristics are more sensitive to the air distribution for the premixed type, which necessitates proper optimization.

• 대한기계학회논문집B
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• 제37권9호
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• pp.829-836
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• 2013

석탄을 개질한 합성천연가스의 조성에 변화가 있을 경우 화염의 연소특성에 대하여 연구하였다. 본 연구의 목적은 동축 공기 합성천연가스 확산화염을 구현하여 연료조성에 따른 화염안정성과 화염구조, 분광특성, 온도분포를 실험적인 방법으로 연구하는 것이다. 각 화염의 분광특성을 관찰하기 위하여 분광기를 사용하였으며 연소장 내 온도측정을 위하여 K 형 열전대를 사용하였다. 연료 분사기 출구속도는 $u_F$ =5~40 m/s 사이에서 조절하였고 공기 분사기 출구속도는 $u_A$ =0~0.43 m/s 사이에서 조절하였다. 연소 동특성에 대한 실험을 통해 합성천연가스에 수소 성분이 증가하면 화염안정화 영역이 증가하고 부상화염 높이가 낮아져 화염길이가 짧아지는 것을 알 수 있었다.