• Title/Summary/Keyword: 줄무늬 화염

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A Study on Transition of Flame Extinction at Low Strain Rate Counterflow Flames (저신장율 대향류화염에서 화염소화에 있어서 천이에 대한 연구)

  • Park, Dae-Geun;Park, Jeong;Kim, Jeong-Soo;Bae, Dae-Suk
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2009.11a
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    • pp.197-201
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    • 2009
  • Experiments were conducted to study the transition of shrinking flame disk to flame hole in counterflow diffusion flames. The studies of transition are well described by varying burner diameters, global strain rate and velocity ratio. It is experimentally verified that radial conduction heat loss is affected at even high strain rate flames for appropriately small burner diameters. It is also shown that flame extinction modes are grouped into three and particularly, hole or stripe is observed in sufficiently high strain rate flames. There exists critical radius according to burner diameter which divide flame extinction modes into three parts.

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Propagation Behavior and Structural Variation of C3H8-Air Premixed Flame with Frequency Change in Ultrasonic Standing Wave (정상초음파의 주파수 변화에 따른 C3H8-Air 예혼합화염의 전파거동 및 구조변이)

  • Lee, Sang Shin;Seo, Hang Seok;Kim, Jeong Soo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.38 no.2
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    • pp.173-181
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    • 2014
  • The propagation behavior and structural variation of a premixed propane/air flame with frequency change in an ultrasonic standing wave at various equivalence ratios were experimentally investigated using Schlieren photography and pressure measurement. The propagating flame was observed in high-speed Schlieren images, allowing local flame velocities of the moving front to be analyzed in detail. The study reveals that the distorted flame front and horizontal splitting in the burnt zone are due to the ultrasonic standing wave. Vertical locations of the distortion and horizontal stripes are intimately dependent on the frequency of the ultrasonic standing wave. In addition, the propagation velocity of the flame front bounded by the standing wave is greater than that of the flame front without acoustic excitation. As expected, the influence of the ultrasonic standing wave on premixed-flame propagation becomes more prominent as the frequency increases.

A Schlieren-photographic Visualization of the Methane/Air Premixed Flame Propagating inside a Rectangular Tube Locally-perturbed by an Ultrasonic Standing Wave (국소적 정상초음파장에 의해 교란되어 사각튜브형 연소실 내에서 전파하는 메탄/공기 예혼합화염의 슐리렌기법에 의한 가시화)

  • Kim, Min Sung;Kim, Jeong Soo;Hwang, Yeong Yeun
    • Journal of the Korean Society of Propulsion Engineers
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    • v.18 no.4
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    • pp.43-49
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    • 2014
  • This experimental study has been conducted to scrutinize the effects of an ultrasonic standing wave (USW) on the propagating velocity and structure of methane/air premixed flame. Propagating flame was caught by high-speed Schlieren photography, and the variation of flame-behavior was analyzed in detail. It is revealed that horizontal splitting in burnt zone is resulted by the USW, and the flame propagation velocity is augmented due to the strengthened chemical reaction. Evolutionary feature of the flame perturbed by USW, maintaining a pseudo-symmetry of top and bottom flame-front about the propagation axis tends to be free from buoyancy effect.

Numerical Simulations on Nonlinear Behaviors of Diffusional-Thermal Instabilities in Counterflow Diffusion Flames (대향류 확산화염에서 확산-전도 불안정의 비선형 거동에 대한 수치해석)

  • Lee, Su-Ryong;Kim, Jong-Su
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.5
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    • pp.695-702
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    • 2002
  • Nonlinear dynamics of striped diffusion flames, by the diffusional-thermal instability with Lewis numbers sufficiently less than unity, is numerically investigated by examining various two-dimensional flame-structure solutions. The Lewis numbers for fuel and oxidizer are assumed to be identical and an overall single-step Arrhenius-type chemical reaction rate is employed in the model. Particular attention is focused on identifying the flame-stripe solution branches corresponding to each distinct stripe pattern and hysteresis encountered during the transition. At a Damkohler number slightly greater than the extinction Damkohler number, eight-stripe solution first emerges from one dimensional solution. The eight-stripe solution survives Damkohler numbers much smaller than the extinction Damkohler number until the transition to four-stripe solution occurs at the first forward transition Damkohler number. At the second forward transition Damkohler number, somewhat smaller than the first transition Damkohler number, the transition to two-stripe solution occurs. However, anu further transition from two-stripe solution to one-stripe solution is not always possible even if one-stripe solution can be independently accessed for particular initial conditions. The Damkohler number ranges for two-stripe and one-stripe solutions are found to be virtually identical because each stripe is an independent structure if distance between stripes is sufficiently large. By increasing the Damkohler number, the backward transition can be observed. In comparison with the forward transition Damkohler numbers, the corresponding backward transition Damkohler numbers are always much greater, thereby indicating significant hysteresis between the stripe patterns of strained diffusion flames.