• Title, Summary, Keyword: Lewis number induced self-excitation

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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.

Experimental Study on Comparison of 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)

  • Ban, Gyu Ho;Lee, Won June;Park, Jeong;Keel, Sang-In;Yun, Jin-Han;Lim, In Gwon
    • 한국연소학회:학술대회논문집
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    • pp.367-369
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    • 2014
  • A study on laminar coflow jet flames diluted with helium and nitrogen has been conducted to investigate self-excitations. The stability map was provided with a function of nozzle exit velocity and fuel mole fractions of propane or methane. The results show that there exist three types of self-excitations; (1) buoyancy-driven self-excitation (BDSE), (2) Lewis number induced self-excitation coupled with buoyancy (LCB) and (3) Lewis number induced self-excitation (LISE).

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A study on Self-excitations in Laminar Lifted Coflow-jet Flames (층류 동축류 제트 부상화염에서의 자기진동에 관한 실험적 연구)

  • Ban, Gyu Ho;Lee, Won June;Park, Jeong;Keel, Sang-In;Yun, Jin-Han;Lim, In Gwon
    • 한국연소학회:학술대회논문집
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    • pp.129-132
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    • 2014
  • A study on laminar coflow jet flames diluted with helium and nitrogen has been conducted to investigate self-excitations. The stability map was provided with a function of nozzle exit velocity and fuel mole fractions of propane or methane. The results show that there exist three types of self-excitations; (1) buoyancy-driven self-excitation (BDSE), (2) Lewis number induced self-excitation coupled with buoyancy (LCB) and (3) Lewis number induced self-excitation (LISE).

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A Study on Self-excitation in Laminar Lifted Coflow-jet Flames (층류 동축류 제트 부상화염에서의 자기진동에 관한 연구)

  • Van, Kyu Ho;Lee, Won June;Park, Jeong;Kim, Tae Hyung;Park, Jong Ho
    • Journal of the Korean Society of Combustion
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    • v.20 no.1
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    • pp.43-51
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    • 2015
  • A study on laminar jet flames in coflow air diluted with helium has been conducted to investigate self-excitations for various propane mole fractions and nozzle exit velocities. The stability map was represented as a function of nozzle exit velocity and fuel mole fraction for propane. The results show that two types of self-excitation were observed : (1) buoyancy-driven self-excitation (hereafter called BDSE) and (2) Lewis-number induced-self-excitation coupled with (1) (hereafter called LCB) near extinction limit for 9.4 mm nozzle diameter. It was shown that with 0.95 mm nozzle diameter, Lewis-number-induced self-excitation (hereafter LISE) and BDSE could be separated. The differences between the two self-excitations were shown and discussed.

Helieum-dilution Effect of Coflow Air on Self-excitation in Laminar Coflow Jet Flames (층류 동축류 제트에서 공기측 헬륨 희석이 화염진동에 미치는 영향)

  • Lee, Won June;Park, Jeong;Kwon, Oh Boong;Baek, Se Hyun;Ko, Sung Ho
    • Journal of the Korean Society of Combustion
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    • v.17 no.4
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    • pp.51-59
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    • 2012
  • Experimental study in coflow jet flames has been conducted to investigate the helium-dilution effect of coflow air on self-excitation. For various helium mole fractions and jet velocities, two types of self-excitation were observed: buoyancy-driven self-excitation and Lewis-number-induced self-excitation(here after called Le-ISE) coupled with buoyancy-driven one. The difference between buoyancy-driven and Le-ISE is clarified by using the Mie-scattering visualization as well as exploring the different features. The mechanism of Le-ISE is proposed. When the system Damk$\ddot{o}$hler number was lowered, Le-ISE is shown to be launched. Le-ISE is closely related to heat loss, in that it can be launched in even methane jet flame (Lewis number less than unity) with helium-diluted coflow air. Particularly, Le-ISE becomes significant as the Damk$\ddot{o}$hler number decreases and heat-loss becomes significant.

Self-excitation of Edge Flame (에지화염의 자기 진동)

  • Park, Jeong;Youn, Sung Hwan;Chung, Yong Ho;Lee, Won June;Kwon, Oh Boong
    • 한국연소학회:학술대회논문집
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    • pp.167-170
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    • 2012
  • Self-excitations of edge flame were studied in laminar lifted free- and coflow-jet as well as counterflow flames diluted with nitrogen and helium. The self-excitations, originated from variation of edge flame speed and found in the above-mentioned configurations, are discussed. A newly found self-excitation and flame blowout, caused by the conductive heat loss from premixed wings to trailing diffusion flame are described and characterized in laminar lifted jet flames. Some trials to distinguish Lewis-number-induced self-excitation from buoyancy-driven one with O(1.0 Hz) are introduced, and then the differences are discussed. In counterflow configuration, important role of the outermost edge flame in flame extinction is also suggested and discussed.

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Study of Characteristics of Self-Excitation in Lifted Laminar Free-Jet Propane Flames Diluted with Nitrogen (질소 희석된 프로판 자유제트 층류부상화염에 있어서 화염 자기진동 특성에 관한 연구)

  • Yoon, Sung-Hwan;Park, Jeong;Kwon, Oh-Boong;Bae, Dae-Seok
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.34 no.4
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    • pp.399-408
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    • 2010
  • The characteristics of lifted laminar propane flames diluted with nitrogen have been investigated experimentally to elucidate self-excitation and the effects of flame curvature. Flame oscillation modes are classified as follows: oscillation induced by heat loss, a combination of oscillations induced by heat loss and buoyancy, and a combination of the oscillations induced by heat loss and diffusive thermal instability. It is shown that the oscillation induced only by heat loss is not relevant to the diffusive thermal instability and hydrodynamic instability caused by buoyancy; this oscillation is observed under all lift-off flame conditions irrespective of the fuel Lewis number. These experimental evidences are displayed through the analysis of the power spectrum for the temporal variation of lift-off height. The possible mechanism of the oscillation induced by heat loss is also discussed.

Diffusive-Thermal Instability and Buoyancy-Driven Instability in Laminar Attached Free-jet Flames with DC Electric Fields (직류 전기장을 인가한 층류부착화염에서 물질-열 확산 및 부력에 의한 화염진동 비교에 관한 연구)

  • Han, Jong-Kyu;Yoon, Sung-Hwan;Park, Jeong;Yun, Jin-Han;Gil, Sang-In;Seo, Sang-Il;Kim, Young-Ju
    • Journal of the Korean Society of Combustion
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    • v.16 no.3
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    • pp.41-51
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    • 2011
  • In this paper, we describe the behavior of two self-excitations in laminar attached free-jet flames under the influence of DC electric fields, one of buoyancy-driven and the other of diffusion-thermal instability, established from the horizontal and vertical injection. In the horizontal injection with removed buoyancy effect, oscillating flames with the frequency of 1.3 - 7.4 Hz were observed in a certain condition with Lewis number more than unity. On the other hand, it was appeared Lewis number induced self-excitation as well as buoyancy-driven self-excitation in the vertical upward injection with DC electric fields. This behavior had frequency range of 1.6 - 9.4 Hz and was exhibited to attribute the buoyancy effect. Finally, a well-defined division about two self-excitations having similar frequency range is briefly discussed.