• Title/Summary/Keyword: Lifted flame

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Study on Heat-Loss-Induced Self-Excitation in Laminar Lifted Jet Flames (층류제트 부상화염에서 열손실에 의한 자기진동에 관한 연구)

  • Yoon, Sung-Hwan;Park, Jeong;Kwon, Oh-Boong;Kim, Jeong-Soo;Bae, Dae-Seok;Yun, Jin-Han;Keel, San-In
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.35 no.3
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    • pp.309-319
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    • 2011
  • We experimentally investigated lifted propane jet flames diluted with nitrogen to obtain flame-stability maps based on heat-loss-induced self-excitation. We found that heat-loss-induced self-excitations are caused by conductive heat loss from premixed flame branches to trailing diffusion flames as well as soot radiation. The conductive-heat-loss-induced self-excitation at frequencies less than 0.1 Hz is explained well by a suggested mechanism, whereas the oscillation of the soot region induces a self-excitation of lift-off height of the order of 0.1 Hz. The suggested mechanism is also verified from additive experiments in a room at constant temperature and humidity. The heat-loss-induced self-excitation is explained by the Strouhal numbers as a function of the relevant parameters.

Visualization of Combustion by Using Laser Diagnostic Techniques (레이저 진단기법을 이용한 연소 가시화 기술)

  • Chung S. H.;Won S. H.
    • Journal of the Korean Society of Visualization
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    • v.2 no.1
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    • pp.52-56
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    • 2004
  • Several visualization techniques of laser diagnostics are presented for combustion phenomena, including Mie scattering for flow, Rayleigh and Raman scattering spectroscopy for major species, laser-induced fluorescence for minor species, and laser-induced incandescence for soot. These techniques have been applied to understand the various combustion phenomena more clearly, including buoyancy-dominant flow system, diffusion flam oscillation, laminar and turbulent lifted flames, flame propagation along a vortex ring, and soot zone characteristics. The usefulness of laser diagnostics on a better understanding of physical mechanism is demonstrated.

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Study on Flame Oscillations in Laminar Lift-off Butane Flames Diluted with Nitrogen (질소 희석된 부탄 부상화염에 있어서 화염진동에 관한 연구)

  • Yoon, Sung-Hwan;Park, Jeong;Kwon, Oh-Boong;Kim, Jeong-Soo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.34 no.7
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    • pp.729-738
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    • 2010
  • The characteristics of lifted butane flames diluted with nitrogen have been investigated experimentally in order to elucidate the mechanism of individual flame oscillation modes. Flame oscillations in laminar free-jet lift-off flames are classified into the following five regimes: a stabilized lift-off regime (I), a heat-loss-induced oscillation (II), a buoyancy-induced oscillation along with a heat-loss-induced oscillation (III), a combined form of an oscillation prior to blow-out and a heat-loss-induced oscillation (IV), and a combination of an oscillation prior to blow-out and a buoyancy-induced oscillation along with a heat-loss-induced oscillation (V). The characterization of the individual flame oscillations modes are presented and discussed using Strouhal numbers and their relevant parameters by the analysis of the power spectrum for temporal variation of the lift-off height.

An Experimental Study on Liftoff and Reattachment Characteristics in Concentric Burner (프로판 동축류 확산 화염에서 화염 부상과 재부착에 관한 실험적 연구)

  • Park, S.H.;Won, S.H.;Cha, M.S.;Chung, S.H.
    • 한국연소학회:학술대회논문집
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    • 2001.11a
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    • pp.119-124
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    • 2001
  • Propane coflow diffusion flames have been experimentally studied to investigate the liftoff and reattachment characteristics. Flame properties such as velocity and density distribution were measured by LDV and shadowgraphy, respectively. It is shown that as the velocity of coflowing air increases, liftoff velocity decreases nonlinearly in turbulent jets and linearly in laminar jets, while reattachment velocity decreases nonlinearly. Meanwhile, as inner nozzle tip thickness increases, liftoff velocity increases with the reattachment velocity nearly unchanged. Liftoff phenomena in these flames can be categorized into three classes as a function of coflow velocity, such as laminar liftoff, turbulent liftoff, and transient liftoff.

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Effect of Flow Distribution on the Combustion Efficiency In an Entrained-Bed Coal Reactor (분류층 석탄반응로에서 유동분포가 연소성능에 미치는 영향)

  • CHO, Han Chang;SHIN, Hyun Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.8
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    • pp.1022-1030
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    • 1999
  • A numerical study was carried out to analyze the effect of flow distribution of stirred part and plug flow part on combustion efficiency at the coal gasification process in an entrained bed coal reactor. The model of computation was based on gas phase eulerian balance equations of mass and momentum. The solid phase was described by lagrangian equations of motion. The $k-{\varepsilon}$ model was used to calculate the turbulence flow and eddy dissipation model was used to describe the gas phase reaction rate. The radiation was solved using a Monte-Carlo method. One-step parallel two reaction model was employed for the devolatilization process of a high volatile bituminous Kideco coal. The computations agreed well with the experiments, but the flame front was closer to the burner than the measured one. The flow distribution of a stirred part and a plug flow part in a reactor was a function of the magnitude of recirculation zone resulted from the swirl. The combustion efficiency was enhanced with decreasing stirred part and the maximum value was found around S=1.2, having the minimum stirred part. The combustion efficiency resulted from not only the flow distribution but also the particle residence time through the hot reaction zone of the stirred part, in particular for the weak swirl without IRZ(internal recirculation zone) and the long lifted flame.

Non-Reacting Flow Structure of a Low Swirl Combustor with respect to Inlet Velocities (저선회 연소기의 입구 속도에 따른 비반응 유동구조 분석)

  • Jeong, Hwanghui;Lee, Bok Jik;Lee, Keeman
    • Journal of the Korean Society of Propulsion Engineers
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    • v.22 no.6
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    • pp.56-63
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    • 2018
  • In low swirl combustors the flame is lifted above the nozzle to achieve balance between the flame speed and velocity field at the exit of the nozzle. Characterization of the flame liftoff height is important because it affects the stability of the combustor and degradation of the nozzle material. In experiments, a counter-intuitive trend of flame liftoff heights with respect to inlet velocities was observed. To elucidate the complicated flow field in a low swirl combustor having swirl vanes and a turbulence generator, a series of numerical simulations of non-reacting flows was conducted by varying the inlet velocity. The flow structures at the exit of the nozzle with respect to the inlet velocities are investigated to support the observation in the experiments.

A study on Self-excitation in Laminar Lifted Propane Coflow-Jet Flames Diluted with Nitrogen (질소로 희석된 프로판 층류 동축류 제트화염에서의 화염진동에 관한 실험적 연구)

  • Lee, Won June;Park, Jeong;Kwon, Oh Boong;Yun, Jin Han;Keel, Sang In;Kim, Tae Hyung;Kim, Young Ju
    • 한국연소학회:학술대회논문집
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    • 2012.11a
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    • pp.19-22
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    • 2012
  • Experimental study in coflow jet flames has been conducted to investigate effects of adding Helium to coflowing air-side in self-excitation. The Differences between buoyancy-driven and diffusive-thermal self-excitations with the same order of O(1.0 Hz) in self-excitation are explored and discussed in laminar coflow jet flames.

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A Study on Remaining Efficiency of Thermal Straightening after Block Lifting

  • Ha, Yunsok;Yi, Myungsu
    • Journal of Advanced Research in Ocean Engineering
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    • v.1 no.3
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    • pp.148-156
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    • 2015
  • Deck plates of ships or offshore structures would make out-of-plane distortion for their thin thickness. These distortions are usually straightened by thermal straightening such as flame heating method. After thermal straightening, the blocks are lifted and moved by cranes to assemble it at dry-dock stage. After this lifting process, out-of-plane deformation again happens frequently. And then, they continuously cause quality and accuracy problems in the final dry-dock process. So, it takes more time for repair and correction working. According to preceding research, the lifting process by cranes would offset the effect on thermal straightening. The target of this study is to develop a methodology analyzing the remaining efficiency of thermal straightening after block lifting. The development was based on the assumption of yield state at straightening region. Therefore the remaining efficiency was obtained by different stiffness slope while lifting & relieving. The efficiency formula was designed using inherent strain, and we made a table of zero-efficiency by cooling speed and class rule's steels. As a result, if the stress orthogonal to straightened line is calculated during lifting analysis by FEA, the efficiency can be obtained linearly to the values in the table. Finally, even optimized carling position can be designed by considering the regional data from series project and welding region on deck.

Experimental Study on Comparison between Buoyancy Driven and Lewis Number Induced Self-excitations in Laminar Lifted Coflow-jet Flames (층류 동축류 제트 부상화염에서 부력에 의한 자기진동과 루이스 수에 의한 자기진동 비교에 관한 실험적 연구)

  • Lee, Won June;Park, Jeong;Kwon, Oh Boong;Yun, Jin Han;Keel, Sang In
    • Journal of the Korean Society of Combustion
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    • v.19 no.2
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    • pp.21-27
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    • 2014
  • Experimental study in laminar propane coflow jet flames has been conducted to investigate self-excitations. For various propane mole fractions and jet velocities, two types of self-excitation were observed: (1) buoyancydriven self-excitation (hereafter called BDSE) and (2) Lewis-number-induced self-excitation coupled with (1) (hereafter called LCB). The mechanism of Lewis-number-induced self-excitation (hereafter called LISE) is proposed. When the system $Damk\ddot{o}hler$ number was lowered, LISE was shown to be launched. The LISE is closely related to heat loss, such that it can be launched in even helium-diluted methane coflow-jet flame (Lewis number less than unity). Particularly, The LISE becomes significant as the $Damk\ddot{o}hler$ number decreases and heat-loss is excessively large.

Effect of AC Electric Fields on Flow Instability in Laminar Jets (층류제트유동 불안정성에 미치는 교류 전기장 효과)

  • Kim, Gyeong Taek;Lee, Won June;Cha, Min Suk;Park, Jeong;Chung, Suk Ho;Kwon, Oh Boong;Kim, Min Kuk;Lee, Sang Min
    • Journal of the Korean Society of Combustion
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    • v.21 no.3
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    • pp.1-6
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    • 2016
  • The effect of applied electric fields on jet flow instability was investigated experimentally by varying the direct current (DC) voltage and the alternating current (AC) frequency and voltage applied to a jet nozzle. We aimed to elucidate the origin of the occurrence of twin-lifted jet flames in laminar jet flow configuration, which occur when AC electric fields are applied. The results indicate that a twin-lifted jet flames originates from cold jet instability, caused by interactions between negative ions in the jet flow via electron attachment as $O_2+e{\rightarrow}O_2{^-}$ when AC electric fields are applied. This was confirmed by experiments in which a variety of gaseous jets were ejected from a nozzle to which DC voltages and AC frequencies and voltages were applied, with ambient air between two deflection plates connected to a DC power source. Experiments in which jet flows of several gases were ejected from a nozzle and AC electric fields were applied in coflow-nitrogen provided further evidence. The flow instability occurred only for oxygen and air jets. Additionally, jet instability occurred when the applied frequency was less than 80 Hz, corresponding to the characteristic collision response time. The effect of AC electric fields on the overall structure of the jet flows is also reported. Based on these results, we propose a mechanism to reduce jet flow instability when AC electric fields are applied to the nozzle.