• Title, Summary, Keyword: Self-excitation

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A Comparative Study Between Diffusive-thermal and Buoyancy-driven Self-excitations in Laminar Free Jet Flames with Applied DC Electric Fields (직류전기장이 인가된 층류제트화염에서 물질 -열 확산과 부력에 의한 진동비교에 관한 연구)

  • Han, Jong-Kyu;Yoon, Sung-Hwan;Park, Jeong;Kwon, Oh-Boong;Kim, Tae-Hyung;Park, Jong-Ho
    • Journal of the Korean Society of Combustion
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    • v.17 no.1
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    • pp.37-47
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    • 2012
  • Experimental study on comparison of diffusive-thermal self-excitation with buoyancy-driven one due to accumulation of partially premixed, preheated mixture in front of edge flame was conducted in horizontally and vertically injected laminar free-jet flames with an applied DC electric field of -10 kV. The application of horizontal injection method with the DC electric field to jet flames was experimentally designed to suppress heat-loss-induced self-excitation and thereby to highlight the definite difference between both diffusive-thermal and buoyancy-driven self-excitations with the same order of O(1.0 Hz), in that diffusive-thermal self-excitation has not been so far found experimentally in laminar jet flames. Flame stability maps in vertically and horizontally injected jet flames are presented. The distinct modes of individual self-excitation are shown to be well described by their own phase diagrams. The results show that buoyancy-driven self-excitation due to the accumulation of partially premixed, preheated mixtures in front of edge flame is branched from the buoyancy-induced self-excitation with O(10 Hz) due to a flame flicker. Once the buoyancy-driven self-excitation appears, it suppresses buoyancy-induced as well as diffusive-thermal self-excitation. The key characteristics for individual self-excitation are discussed and their functional dependencies of Strouhal number upon related physical parameters are also presented.

Effect of Coflow Air Velocity on Heat-loss-induced Self-excitation in Laminar Lifted Propane Coflow-Jet Flames Diluted with Nitrogen (질소로 희석된 프로판 동축류 층류 제트 부상화염에서 열손실에 의한 자기진동에 대한 동축류 속도 효과)

  • Lee, Won-June;Yoon, Sung-Hwan;Park, Jeong;Kwon, Oh-Boong;Park, Jong-Ho;Kim, Tae-Hyung
    • Journal of the Korean Society of Combustion
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    • v.17 no.1
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    • pp.48-57
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    • 2012
  • Laminar lifted propane coflow-jet flames diluted with nitrogen were experimentally investigated to determine heat-loss-related self-excitation regimes in the flame stability map and elucidate the individual flame characteristics. There exists a critical lift-off height over which flame-stabilizing effect becomes minor, thereby causing a normal heat-loss-induced self-excitation with O(0.01 Hz). Air-coflowing can suppress the normal heat-loss-induced self-excitation through increase of a Peclet number; meanwhile it can enhance the normal heat-lossinduced self-excitation through reducing fuel concentration gradient and thereby decreasing the reaction rate of trailing diffusion flame. Below the critical lift-off height. the effect of flame stabilization is superior, leading to a coflow-modulated heat-loss-induced self-excitation with O(0.001 Hz). Over the critical lift-off height, the effect of reducing fuel concentration gradient is pronounced, so that the normal heat-loss-induced self-excitation is restored. A newly found prompt self-excitation, observed prior to a heat-loss-induced flame blowout, is discussed. Heat-loss-related self-excitations, obtained laminar lifted propane coflow-jet flames diluted with nitrogen, were characterized by the functional dependency of Strouhal number on related parameters. The critical lift-off height was also reasonably characterized by Peclet number and fuel mole fraction.

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.

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.

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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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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Analysis of Operating Characteristic of Self Excited Induction Generator with Steinmetz Connection (스타인메츠결선 자기여자 유도발전기의 운전특성 분석)

  • Kang, Sang-Su;Jwa, Chong-Keun
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.57 no.4
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    • pp.383-387
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    • 2008
  • This paper analyzes the operation characteristics of a self excited induction generator with Steinmetz connection. For this analysis, the symmetrical components analysis is used to obtain the related expressions and the excitation capacitance and the magnetizing reactance are determined in turn by the condition of self excitation which includes the input impedance of the generator as viewed across load terminals. Two simultaneous equations of the condition of self excitation itself are solved by using the real and imaginary function in an application software. This method is applied to simulate the operation characteristics when the generator is driven at rated speed and the specified excitation capacitor is connected across the lagging phase. The results show that better operation characteristics except generated frequency are obtained by using relatively large excitation capacitance and resistive load.

Eliashberg Calculation of the Momentum-Resolved Self-Energy for the Cuprate Superconductors Induced by the Spin Fluctuations (구리 산화물 계열 초전도체에서의 스핀 요동에 의한 자체 에너지의 엘리아시버그 계산)

  • Hong, Seung-Hwan;Choi, Han-Yong
    • Progress in Superconductivity
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    • v.13 no.3
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    • pp.146-150
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    • 2012
  • We solve the momentum resolved d-wave Eliashberg equation employing the magnetic excitation spectrum from the inelastic neutron scattering on the LSCO superconductors reported by Vignolle et al. The magnetic excitation spectrum exhibits 2 peaks: a sharp incommensurate peak at 18 meV at momentum (${\pi}$, ${\pi}{\pm}{\delta}$) and (${\pi}{\pm}{\delta}$, ${\pi}$) and another broad peak near 40~70 meV at momentum (${\pi}$, ${\pi}$). Above 70 meV, the magnetic excitation spectrum has a long tail that is shaped into a circle centered at (${\pi}$, ${\pi}$) with ${\delta}$. The sign of the real part of the self-energy is determined by the momentum position of the peaks of the magnetic excitation spectrum and bare dispersion. We will discuss the effects of the each component of the magnetic excitation spectrum on the self-energy, the pairing self-energy.

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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A Study on Novel Excitation Method to Reduce Acoustic Noise in SRM Drive (소음저감을 위한 SRM 드라이브의 새로운 여자방식에 관한 연구)

  • Mun, Jae-Won;O, Seok-Gyu;An, Jin-U;Hwang, Yeong-Mun
    • The Transactions of the Korean Institute of Electrical Engineers B
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    • v.48 no.6
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    • pp.287-293
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    • 1999
  • A new excitation method of switched reluctance motor drive is described in this paper. This excitation method produces reluctance torque by mutual action between two phases as well as conventional self reluctance torque due to two phase excitation at a time. In other words, the change of self inductance and mutual inductance are used to produce torque. This paper suggests the operational principle, the mechanism of torque product of switched reluctance motor with two phase excitation. The acoustic noise characteristics of two phase excitation method are described against that of conventional excitation method. The energy conversion ratio is increased because the next phase is excited following one phase excited at the two phase excitation method. Acoustic noise is lower than that of conventional SRM because one of the next two phase is excited already when torque develope.

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