• Title, Summary, Keyword: Extinction

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A Study on Flame Extinction Behavior in Downstream Interaction between SNG/Air Premixed Flames (SNG/Air 예혼합 화염들의 하류상호작용에 있어서 화염 소화 거동에 관한 연구)

  • Sim, Keunseon;Lee, Keeman
    • Journal of the Korean Society of Combustion
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    • v.21 no.4
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    • pp.48-60
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    • 2016
  • Experimental and numerical studies were conducted to investigate flame behaviors near flammable limits for downstream-interacting SNG-air premixed flames in a counter-flow configuration. The SNG fuel consisted of a methane, a propane, and a hydrogen with volumetric ratios of 91, 6, and 3%, respectively. The most appropriate priority for some reliable reaction mechanisms examined was given to the mechanism of UC San diego via comparison of lean extinction limits attained numerically with experimental ones. Flame stability map was presented with a functional dependencies of lower and upper methane concentrations in terms of global strain rate. The results show that, at the global strain rate of $30s^{-1}$, lean extinction boundary is slanted while rich extinction one is relatively less inclined because of the dependency of such extinction boundary shapes on deficient reactant Lewis number governed by methane mainly. Further increase of global strain rate forces both extinction boundaries to be more slanted and to be shrunk, resulting in an island of extinction boundary and subsequently one flame extinction limit. Extinction mechanisms for lean and rich, symmetric and asymmetric extinction boundary were identified and discussed via heat losses and chemical interaction.

Extinction Limits of Low Strain Rate Counterflow Nonpremixed Flames in Normal Gravity (정상 중력장에서 낮은 스트레인율을 갖는 대향류 비예혼합화염의 소화한계)

  • Oh, Chang-Bo;Choi, Byung-Il;Kim, Jeong-Soo;Hamins, Anthony;Park, Jeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.9
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    • pp.997-1005
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    • 2005
  • The extinction characteristics of low strain rate normal gravity (1-g) nonpremixed methane-air flames were studied numerically and experimentally. A time-dependent axisymmetric two-dimensional (2D) model considering buoyancy effects and radiative heat transfer was developed to capture the structure and extinction limits of 1-g flames. One-dimensional (1D) computations were also conducted to provide information on 0-g flames. A 3-step global reaction mechanism was used in both the 1D and 2D computations to predict the measured extinction limit and flame temperature. A specific maximum heat release rate was introduced to quantify the local flame strength and to elucidate the extinction mechanism. Overall fractional contribution by each term in the energy equation to the heat release was evaluated to investigate the multi-dimensional structure and radiative extinction of 1-g flames. Images of flames were taken for comparison with the model calculation undergoing extinction. The two-dimensional numerical model was validated by comparing flame temperature profiles and extinction limits with experiments and ID computation results. The 2D computations yielded insight into the extinction mode and flame structure of 1-g flames. Two combustion regimes depending on the extinction mode were identified. Lateral heat loss effects and multi-dimensional flame structure were also found. At low strain rates of 1-g flame ('Regime A'), the flame is extinguished from the weak outer flame edge, which is attributed to multi-dimensional flame structure and flow field. At high strain rates, ('Regime B'), the flame extinction initiates near the flame centerline due to an increased diluent concentration in reaction zone, which is the same as the extinction mode of 1D flame. These two extinction modes could be clearly explained with the specific maximum heat release rate.

An Experimental Study on the Extinction Limit Extension of Unsteady Counterflow Diffusion Flames (비정상 대향류 확산 화염의 소화 한계 확장에 대한 실험적 연구)

  • Lee Uen Do;Lee Ki Ho;Oh Kwang Chul;Lee Eui Ju;Shin Hyun Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.3
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    • pp.390-401
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    • 2005
  • In this study, extinction limit extension of unsteady $(CH_{4}+N_{2})$/air diffusion flames was investigated experimentally. A spatially locked flame in an opposing jet burner was perturbed by linear velocity variation, and time-dependent flame luminosity, transient maximum flame temperature and OH radical were measured over time with the high speed camera, Rayleigh scattering method and OH laser-induced fluorescence, respectively. Unsteady flames survive at strain rates that are much higher than the extinction limit of steady flames, and unsteady extinction limits extend as the slope of the strain rate increases or the initial strain rate decreases. We verified the validity of the equivalent strain rate concept by comparing the course of unsteady extinction process and steady extinction process, and it was found that the equivalent strain rate concept represents well the unsteady effect of a convective-diffusive zone. To investigate the reason of the unsteady extinction limit extension, we subtracted the time lag of the convective-diffusive zone by using the equivalent strain concept. Then the modified unsteady extinction limits become smaller than the original unsteady extinction limits, however, the modified unsteady extinction limits are still larger than the steady extinction limits. These results suggest that there exist the unsteady behavior of a diffusive-reactive zone near the extinction limit due to the chemical non-equilibrium states associated with unsteady flames.

The extinction of unsteady counterflow diffusion flame without the retardation effect of a mixing layer (혼합층의 지연효과를 배제한 비정상 대향류 확산 화염의 소화)

  • Lee, Uen-Do;Oh, Kwang-Chul;Lee, Ki-Ho;Lee, Chun-Bum;Lee, Eui-Ju;Shin, Hyun-Dong
    • 한국연소학회:학술대회논문집
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    • pp.93-101
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    • 2003
  • The extinction of unsteady diffusion flame was experimentally studied in an opposing jet counterflow burner using diluted methane. The stabilized flame was perturbed by linearly varying velocity change that was generated by pistons installed on both sides of the air and fuel stream. As the results, the extinction of unsteady flame is dependent not only on the history of unsteadiness, but also on the initial condition. We found that there are several unsteady effects on the flame extinction. First, the extinction strain rates of unsteady cases are extended well beyond steady state extinction limits. Second, as the slope of the strain rate change increases, the unsteady extinction strain rate becomes larger. Third, the extension of unsteady extinction strain rate becomes smaller as the initial strain rate increases. We also found that the extension of the extinction limit mainly results from the unsteady response of the reaction zone because there is no retardation effect of a mixing layer for our experimental condition.

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ON THE HOMOGENEITY OF THE EXTINCTION LAW IN OUR GALAXY

  • Bondar, A.;Galazutdinov, G.;Patriarchi, P.;Krelowski, J.
    • Journal of The Korean Astronomical Society
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    • v.39 no.3
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    • pp.73-80
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    • 2006
  • We analyze the extinction law towards several B1V stars-members of our Galaxy, searching for possible discrepancies from the galactic average extinction curve. Our photometric data allow to build extinction curves in a very broad range: from extreme UV till infrared. Two-colour diagrams, based on the collected photometric data from the ANS UV satellite, published UBV measurements and on the infrared 2MASS data of the selected stars, are constructed. Slopes of the fitted straight lines are used to build the average extinction curve and to search for discrepant objects. The selected stars have also been observed spectroscopically from the Terskol and ESO Observatories; these spectra allow to check their Sp/L's. The spectra of only about 30% of the initially selected objects resemble closely that of HD144470, considered as the standard of B1 V type. Other spectra either show some emission features or belong clearly to another spectral types. They are not used to build the extinction curve. Two-colour diagrams, constructed for the selected B1 V stars, showing no emission stellar features, prove that the interstellar extinction law is homogeneous in the Galaxy. Both the shape of the curve and the total-to-selective extinction ratio do not differ from the galactic average and the canonical value(3.1) respectively. The circumstellar emissions usually cause some discrepancies from the average interstellar extinction law; the discrepancies observed in the extraterrestrial ultraviolet, usually follow some misclassifications.

Changes of the Flame Temperature and OH Radical in the Unsteady Extinction Process (비정상 소화 과정에서의 화염 온도 및 OH 라디칼의 변화)

  • Lee, Uen-Do;Lee, Ki-Ho;Oh, Kwang-Chul;Shin, Hyun-Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.12
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    • pp.1557-1566
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    • 2004
  • A flame extinction phenomenon is a typical unsteady process in combustion. Flame extinction is characterized by various physical phenomena, such as convection, diffusion, and the production of heat and mass. Flame extinction can be achieved by either increasing the strain rate or curvature, by diluting an inert gas or inhibitor, or by increasing the thermal or radiant energy loss. Though the extinction is an inherently transient process, steady and quasi-steady approaches have been used as useful tools for understanding the flame extinction phenomenon. Recently, unsteady characteristics of flames have been studied by many researchers, and various attempts have been made to understand unsteady flame behavior, by using various extinction processes. Representative parameters for describing flame, such as flame temperature, important species related to reactions, and chemi-luminescence of the flame have been used as criterions of flame extinction. In these works, verification of each parameter and establishing the proper criterions of the extinction has been very important. In this study, a time-dependent flame temperature and an OH radical concentration were measured using optical methods, and the instantaneous change of the flame luminosity was also measured using a high-speed ICCD (HICCD) camera. We compare the unsteady extinction points obtained by three different methods, and we discuss transient characteristics of maximum flame temperature and OH radical distribution near the extinction limit.

A Novel Vertical Directional Coupler Switch with Switching Operation-Induced, Extinction Ratio-Adjusted, and Extinction Ratio-Enhanced Sections

  • Cho, Sung-Chan;Hong, Hyun-Ha;Yang, Choong-Reol;Choi, Jee-Yon;Kang, Min-Ho;Hwang, Hyun-Yong;Choi, Young-Woo;Kim, Hae-Geun;Jung, Byung-Min;Kim, Boo-Gyoun
    • ETRI Journal
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    • v.24 no.2
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    • pp.109-116
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    • 2002
  • We propose a novel very short (< $300{\mu}m$) vertical directional coupler switch with high extinction ratios larger than 30 dB. The device consists of a switching operation induced section (SOIS), an extinction ratio adjusted section (ERAS), and an extinction ratio enhanced section (ERES). These are achieved by changing the refractive index of one core. The switching operation is induced by changing the refractive index of one core in the SOIS. The improvement of extinction ratios larger than 30 dB for both the cross and bar states is made by controlling the asymmetry of the refractive indices of both cores in the ERES. Through the ERAS, different extinction ratios between the cross and bar states at the end of the SOIS are changed to the same value. For this reason, the optimum asymmetry of the refractive indices of the cores for the maximum extinction ratios and the lengths of ERES are the same for cross and bar states. Design guidelines for high extinction ratios with large tolerances are presented.

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Amygdala Depotentiation and Fear Extinction

  • Choi, Suk-Woo
    • Proceedings of the Korean Society of Applied Pharmacology
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    • pp.33-45
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    • 2008
  • Auditory fear memory is thought to be maintained by fear conditioning-induced potentiation of synaptic efficacy. The conditioning-induced potentiation has been shown to be maintained, at least in part, by enhanced expression of surface AMPA receptor (AMPAR) at excitatory synapses in the lateral amygdala (LA). Depotentiation, reversal of conditioning-induced potentiation, has been proposed as a cellular mechanism for fear extinction. However, a direct link between depotentiation and extinction has not yet been tested. To address this, we applied both ex vivo and in vivo approaches to rats in which fear memory had been consolidated. We found a novel form of ex vivo depotentiation; the depotentiation reversed conditioning-induced potentiation at thalamic input synapses onto the LA (T-LA synapses) ex vivo, and it could be induced only when both NMDA and metabotropic glutamate receptors were co-activated. Extinction returned the enhanced T-LA synaptic efficacy observed in conditioned rats to baseline and occluded the depotentiation. Consistently, extinction reversed conditioning-induced enhancement of surface expression of AMPAR subunits in LA synaptosomal preparations. A GluR2-derived peptide that blocks regulated AMPAR endocytosis inhibited depotentiation, and microinjection of a cell-permeable form of the peptide into the LA attenuated extinction. Our results are consistent with the use of depotentiation to weaken potentiated synaptic inputs onto the LA during extinction, and they provide strong evidence that AMPAR removal at excitatory synapses in the LA underlies extinction. The results described here are in line with previous findings. Neural activity in the LA has been shown to decrease after extinction in the rat and human. The NMDAR dependency of the depotentiation fits nicely with a large body of evidence that fear extinction depends upon amygdala NMDARs. Similarly, blockade of metabotropic glutamate recepotrs in the LA has recently been shown to attenuate fear extinction.

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A Study on the Concentration and Light Extinction of Atmospheric Aerosol in Seoul (서울 대기 에어로솔의 농도와 광소산에 관한 연구)

  • 김필수;오미석;김의훈
    • Journal of Korean Society for Atmospheric Environment
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    • v.7 no.3
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    • pp.227-234
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    • 1991
  • This study deals with concentration and light extinction of atmospheric aerosol in Seoul. From the measured aerosol size distribution for particle diameter ranging from 0.01 $\mum \sim 1.0 \mum$, extinction coefficient is calculated using the Mie theory. The results show that the diurnal variation of aerosol concentration, in general, reveals the lowest concentration in early morning and afternoon, while the highest at about 8 O'clock owing to the heavy traffic and accumulation of air pollution in the low atmosphere. However, aerosol concentration and extinction coefficient on April 7 give low values due to the advective wind. On the other hand, high aerosol concentration and extinction coefficenat are recorded on April 10 although solar radiation is weak. From the distribution of extinction coefficient we can find that aerosol particles of 0.1 $\mum \sim 1.0 \mum$ in diameter are highly effective on light extinction.

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A numerical analysis on the extinction of hydrogen-oxygen diffusion flames at high pressure (고압하에서 수소-산소 확산화염의 소염 특성에 관한 수치 해석)

  • Son, Chae-Hun;Kim, Jong-Su;Jeong, Seok-Ho;Lee, Su-Ryong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.9
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    • pp.1174-1184
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    • 1997
  • Extinction characteristics of pure hydrogen-oxygen diffusion flames, at high pressures in the neighborhood of the critical pressure of oxygen, is numerically studied by employing counterflow diffusion flame as a model flame let in turbulent flames in rocket engines. The numerical results show that extinction strain rate increases almost linearly with pressure up to 100 atm, which can be explained by comparison of the chain-branching-reaction rate with the recombination-reaction rate. Since contributions of the chain-branching reactions, two-body reactions, are found to be much greater than those of the recombination reactions, three-body reactions, extinction is controlled by two-body reactions, thereby resulting in the linearity of extinction strain rate to pressure. Therefore, it is found that the chemical kinetic behaviors don't change up to 100 atm. Consideration of the pressure fall-off reactions shows a slight increase in extinction strain rate, but does not modify its linearity to pressure. The reduced kinetic mechanisms, which were verified at low pressures, are found to be still valid at high pressures and show good qualitative agreement in prediction of extinction strain rates. Effect of real gas is negligible on chemical kinetic behaviors of the flames.