• Title/Summary/Keyword: Standing wave ratio

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Effects of the Equivalence Ratio on Propagation Characteristics of CH4-Air Premixed Flame Intervened by an Ultrasonic Standing Wave (정상초음파가 개재하는 CH4-Air 예혼합화염의 전파특성에 대한 당량비의 영향)

  • Seo, Hang Seok;Lee, Sang Shin;Kim, Jeong Soo
    • Journal of the Korean Society of Propulsion Engineers
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    • v.17 no.2
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    • pp.16-23
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    • 2013
  • An experimental study has been conducted to investigate the effects of equivalence ratio on the propagation characteristics of $CH_4$-air premixed flame intervened by an ultrasonic standing wave. A Schlieren photography was used for the flame structure visualization, and the flame propagation behavior was investigated in detail throughout the post-processing analysis. It is found that the structural variation of methane/air premixed flame caused by the intervention of ultrasonic standing wave give rise to the enhancement of combustion reaction and flame propagation velocity. Effectiveness of the standing wave on the flame velocity decreases as the equivalence ratio increases. Larger flame velocity with the standing wave becomes undistinguishable in a specific range of equivalence ratios.

Combustion Characteristics According to the Equivalence Ratio of Hydrocarbon Fuel/Air Premixture Excited by Ultrasonic Standing Wave (정상초음파가 인가된 탄화수소계 연료/공기 혼합물의 당량비에 따른 연소특성)

  • Kim, Min Cheol;Bae, Seong Hun;Hong, Joon Yeol;Kim, Jeong Soo
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2017.05a
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    • pp.628-631
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    • 2017
  • An experimental study of the combustion characteristics according to the equivalence ratio of hydrocarbon fuel/air premixture excited by ultrasonic standing wave are presented. The image of the propagating flame was acquired using a high-speed camera, and the combustion characteristics of each fuel were closely observed through image processing. it was conformed that ultrasonic standing wave has been found to stimulate the combustion reaction in the stoichiometric ratio.

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Agitation Effects of an Ultrasonic Standing Wave on the Dynamic Behavior of Methane/Air Premixed Flame (메탄/공기 예혼합화염의 동역학적 거동과 정상초음파의 교반)

  • Seo, Hang-Seok;Lee, Sang-Shin;Kim, Jeong-Soo
    • Journal of the Korean Society of Propulsion Engineers
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    • v.16 no.3
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    • pp.16-23
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    • 2012
  • This study has been conducted to scrutinize agitation effects of an ultrasonic standing wave on the dynamic behavior of methane/air premixed flame. The propagating flame was caught by high-speed Schlieren images, through which local flame velocities of the moving front were analyzed in unprecedent detail. It is revealed that the propagation velocity agitated by the ultrasonic standing wave is greater than that without agitation at the stoichiometric ratio: the velocity enhancement diminishes as the equivalence ratio approaches upper flammability limit or lower flammability limit. Also, vertical locations of the wave-affected frontal distortions do not vary appreciably, unless the propagating-mode characteristics (pressure amplitude and driving frequency) of ultrasonic standing wave were not changed.

Frequency-Equivalence Ratio Correlation Analysis of Methane-Air Premixed Flame Influenced by Ultrasonic Standing Wave (II) (정상초음파의 영향을 받는 메탄-공기 예혼합화염의 주파수-당량비 상관도 분석(II))

  • Kim, Min Sung;Bae, Dae Seok;Kim, Jeong Soo
    • Journal of the Korean Society of Propulsion Engineers
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    • v.19 no.4
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    • pp.45-51
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    • 2015
  • An experimental study was performed for the analysis of frequency-equivalence ratio correlation in the methane-air premixed flame influenced by ultrasonic standing wave. The propagating flame was caught by high-speed Schlieren photography, and the variation of flame-behavior including the flame structure was investigated in detail employing a post-processing analysis of the high-speed images. It was found that a structural variation and propagation-velocity augmentation of the methane-air premixed flame by the intervention of ultrasonic standing wave were more caused off around the stoichiometry. Also, a dependency of the flame behaviors on the driving frequency and equivalence ratio of the reactants was confirmed.

Interacting Effects of an Ultrasonic Standing-wave on the Propagation Behavior and Structural Stabilization of Propane/Air Premixed Flame (프로판/공기 예혼합화염의 전파거동 및 구조안정화에 대한 정상초음파의 간섭효과)

  • Lee, Sang Shin;Seo, Hang Seok;Kim, Jeong Soo
    • Journal of the Korean Society of Propulsion Engineers
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    • v.16 no.6
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    • pp.1-8
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    • 2012
  • An experimental study has been conducted to scrutinize into the influence of ultrasonic standing wave on the propagating behavior and structural stabilization of propane/air premixed flame at various equivalence ratios in half-open rectangular duct. Evolutionary features of the flame fronts are caught by high-speed images, and the variation of flame structure and local flame velocities along the propagation are analyzed. It is revealed that the propagation velocity agitated by the ultrasonic standing wave is greater than that without the agitation: the velocity enhancement diminishes as the equivalence ratio approaches the stoichiometric. Influence of standing wave on the flame overwhelms that of the buoyancy which slants the flame front towards top of the duct, and thus the standing wave contributes to the structural stabilization of propane/air premixed flame.

A Structural Behavior of the Propane/Air Premixed Flame Interacting with an Ultrasonic Standing-wave (정상초음파가 개재하는 프로판/공기 예혼합화염의 구조 거동)

  • Lee, Sang-Shin;Seo, Hang-Seok;Kim, Jeong-Soo;Lee, Do-Hyung
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2012.05a
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    • pp.294-299
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    • 2012
  • An investigation into the influence of ultrasonic standing wave on the structural behavior of propane/air premixed flame has been made to get a clue to the combustion reaction acceleration and combustion instability, as well. Visualization technique utilizing the Schlieren method was employed for the observation of structural variation of the premixed flame. The flame shape and propagation velocity were measured according to the variation of equivalence ratio. It was found that the standing wave distorted the flame front and expedited a transition to the flame with turbulent nature.

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Effects of Ultrasonic Standing Wave on the Ultrasonically-atomized Aerosol Flame Injected through a Slit-jet Nozzle (Slit-jet 노즐을 통과한 초음파 무화 에어로졸 화염에 정상초음파가 미치는 영향)

  • Ahn, Hyun Jong;Kang, Yun Hyeong;Kim, Jeong Soo
    • Journal of the Korean Society of Propulsion Engineers
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    • v.24 no.6
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    • pp.53-60
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    • 2020
  • In liquid-fuel spray combustion, an experimental study was conducted to observe the effect of ultrasonic excitation on the ultrasonically-atomized liquid fuel flame by controlling pressure field through an ultrasonic standing wave. Flame of the ultrasonically-atomized kerosene aerosol was visualized by using a high speed camera, DSLR, and Schlieren photography. The amount of fuel consumed was obtained by a precise flow-rate measurement technique during combustion, through which the ratio of carrier gas (air) to fuel mass was able to be obtained, too. As a result, it could be found that the combustion reaction-rate of the liquid-fuel aerosol was increased by applying an ultrasonic standing wave to the secondary flame zone of the flame.

Changes in the Spinal Motor Neuron Excitability Depending on Postural Changes in Post Stoke Hemiplegics (뇌졸중 후 편마비 환자의 체위변화에 따른 척수운동신경원 흥분성 변화)

  • Park, Young-Hyun;Kim, Yong-Nam;Kim, Su-Hyon;Oh, Seok;Choi, Ji-Ho;Kim, Tae-Youl
    • The Journal of Korean Physical Therapy
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    • v.22 no.4
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    • pp.15-20
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    • 2010
  • Purpose: The purpose of this study was to measure changes in the H-reflex and V wave under loading conditions (e.g. prone and standing position) and to investigate whether postural change would affect the H-reflex and V wave in post stroke hemiplegic patients. Methods: Thirty persons with hemiplegia resulting from stroke (20 males, 10 females) participated in this study. Electromyography (EMG) was used to electrically stimulate and record the soleus H-reflexes and V waves under various loading conditions. The normality of the distribution of each variable (H latency, $H_{max}/M_{max}$ ratio, $V_{max}/M_{max}$ ratio) was tested using the Kolmogorov-Smirnov test. The means of normally distributed continuous data were assessed by independent t-test (${\alpha}$=0.05). Results: There were statistically significant differences in $H_{max}/M_{max}$ ratio (p<0.01), $V_{max}/M_{max}$ ratio (p<0.01), H latency (p<0.01) among the prone and standing position. Conclusion: We found that the H-reflex and V wave in standing position was more active to weight bearing load than prone position.

An Analytical Solution of Dynamic Responses for Seabed under Coexisting Fields of Flow and Partial Standing Wave with Arbitrary Reflection Ratio (흐름과 임의반사율을 갖는 부분중복파와의 공존장하에서 해저지반내 동적응답의 해석해)

  • Lee, Kwang-Ho;Kim, Dong-Wook;Kang, Gi-Chun;Kim, Do-Sam;Kim, Tae-Hyung;Na, Seung-Min
    • Journal of the Korean Geotechnical Society
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    • v.31 no.6
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    • pp.27-44
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    • 2015
  • An analytical solution of dynamic responses for seabed in finite and infinite thicknesses including shallow has been developed under flow and partial standing wave with arbitrary reflection ration coexisting field at a constant water depth condition. In the analytical solution, a field was simply transited to a coexisting field of progressive wave and flow when reflection ratio was 0 and to a coexisting field of fully standing wave and flow when reflection ratio was 1. Based on the Biot's consolidation theory, the seabed was assumed as a porous elastic media with the assumptions that pore fluid is compressible and Darcy law governs the flow. The developed analytical solution was compared with the existing results and was verified. Using the analytical solution the deformation, pore pressure, effective and shear stresses were examined under various given values of reflection ratio, flow velocity, incident wave's period and seabed thickness. From this study, it was confirmed that the dynamic response of seabed was quite different depending on consideration of flow, which causes changing period and length of incident and reflection waves. It was also confirmed that dynamic response significantly depends on the magnitude of reflection ratio.