• Title/Summary/Keyword: ratio variable

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An Experimental Study of the Variable Sonic/supersonic Ejector Systems (가변형 음속/초음속 이젝터 시스템에 관한 실험적 연구)

  • Lee Jun Hee;Kim Heuy Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.5 s.236
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    • pp.554-560
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    • 2005
  • A new method to improve the efficiency of a hydrogen fuel cell system was introduced by using variable sonic/supersonic ejectors. To obtain the variable area ratio of the nozzle throat to ejector throat which controls the mass flow rate of the suction flow, the ejectors used a movable cylinder inserted into a conventional ejector-diffuser system. Experiments were carried out to understand the flow characteristics inside the variable ejector system. The secondary mass flow rates of subsonic and supersonic ejectors were examined by varying the operating pressure ratio and area ratio. The results showed that the variable sonic/supersonic ejectors could control the recirculation ratio by changing the throat area ratio, and also showed that the recirculation ratio increased fur the variable sonic ejector and decreased for the variable supersonic ejector, as the throat area ratio increases.

An Experimental Study on the Variable Sonic Ejector System (가변형 음속 이젝터 시스템에 관한 실험적 연구)

  • Lee, Jun-Hee;Jung, Sung-Jae;Kim, Heuy-Dong;Koo, Byoung-Soo
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.2035-2040
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    • 2004
  • A cone cylinder is used to obtain variable operation conditions for the sonic ejector-diffuser system. The cone cylinder is designed to move upstream and downstream to change the ejector throat area ratio, thus obtaining variable mass flow rates. The present study investigates the effects of ejector throat area ratio and operating pressure ratio on the entrainment of secondary stream for the variable sonic ejector system. In experiment, the ejector throat area is varied in the range from ${\psi}=11.88$ to 66.69, and the operating pressure ratio from $p_{0p}/p_a=1.25$ to 9.0. The results show that the variable sonic ejector system is suitable for a required entrainment ratio of secondary stream by altering the ejector throat area ratio and operating pressure ratio.

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A Study of a Variable Sonic Ejector Flow

  • Lee, Jun-Hee;Kim, Heuy-Dong
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2004.03a
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    • pp.414-417
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    • 2004
  • A cone cylinder is used to obtain variable operation conditions for the sonic ejector-diffuser system. The cone cylinder is designed to be shifted upstream and downstream to change the ejector throat area ratio, thus obtaining variable mass flow rates. The present study investigates the effects of ejector throat area ratio and operating pressure ratio on the entrainment of secondary stream for the variable sonic ejector system. The study is carried out experimentally. The ejector throat area is varied at the range from Ψ= 11.88 to 66.69, and the operating pressure ratio is changed from $P_{op}$ / $P_{a}$=1.25 to 9.0. The results show that the variable sonic ejector system can be operated to obtain specific entrainment ratio of secondary stream by altering the ejector throat area ratio and operating pressure ratio.o.

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Stress Intensity Factors of Combined Mode(Mode I/II) Crack in a Variable Thickness Plate (두께가 변화하는 부재 내의 혼합모드(모드 I/II) 균열의 응력확대계수)

  • 조명래;양원호;최용식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.8
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    • pp.1875-1882
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    • 1993
  • Variable thickness plates are commonly used as structural members in the majority of industrial sectors. Previous fracture mechanics researches on variable thickness plates were limited to mode I loading cases. In practice, however, cracks are usually located inclined to the loading direction. In this respect, combined mode(mode I/II) stress intensity factors $K_{I}$ and $K_{II}$ at the crack tip for a variable thickness plate were obtained by 3-dimensional finite element analysis. Variable thickness plates containing a slant edge crack were chosen. The parameters used in this study were dimensionless crack $length{\lambda}$, slant $angle{\alpha}$, thickness $ratio{\beta}$ and width ratio{\omega}$. Stress intensity factors were calculated by crack opening displacement(COD) and crack sliding displacement(CSD)method proposed by Ingraffea and Manu.

A Chancteristic of Thermal Efficiency in Order to High Expansion Realization with a Retard of Intake Valve Closing Time in the Low Speed Diesel Engine (저속 디젤기관에서 흡기밸브 닫힘시기 지연시 고팽창 실현을 위한 열효율 특성)

  • Jang Tae-Ik
    • Journal of Advanced Marine Engineering and Technology
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    • v.30 no.1
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    • pp.42-49
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    • 2006
  • In this research. the diesel cycle was thermodynamically interpreted to evaluate the possibility of high efficiency by converting diesel engines to the high expansion diesel cycle, and general cycle features were analyzed after comparing these two cycles. Based on these analyses. an experimental single cylinder a long stroke with high expansion-diesel engine. of which S/B ratio was more than 3, was manufactured. After evaluating the base engine through basic experiments, a diesel engine was converted into the high expansion diesel engine by establish VCR device and VVT system Accordingly, the high expansion diesel cycle can be implemented when the quantity of intake air is compensated by supercharge and the effective compression ratio is maintained at its initial level through the reduction of the clearance volume. In this case, heat efficiency increased by $5.0\%$ at the same expansion-compression ratio when the apparent compression ratio was 20 and the fuel cut off ratio was 2. As explained above, when the atkinson cycle was used for diesel cycle, heat efficiency was improved. In order to realize high expansion through retarding the intake value closing time, the engine needs to be equipped with variable valve timing equipment, variable compression ratio equipment and supercharged pressure equipment. Then a high expansion diesel cycle engine is realized.

An Experimental Study on the Shift Characteristics of a Metal Belt Type Continuously Variable Transmission (CVT) (금속벨트식 무단변속기(CVT)의 변속특성에 관한 실험적 연구)

  • 이충섭
    • Transactions of the Korean Society of Automotive Engineers
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    • v.5 no.6
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    • pp.36-43
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    • 1997
  • To cope with quest to improve the fuel economy and vehicle performance, Continuously Variable Transmission with Changing the speed ratio between minimum and maximum ratio by infinite step, is more efficient than conventional multi-ratio transmission. In this paper, to investigate a specific CVT shift ratio diagram and CVT shift characteristics, CVT vehicle was tested on the proving ground and chassis dynamometer. The test results are as follows; CVT can obtain the excellent vehicle performance and fuel economy changing the shift ratio by infinite step, without rapid change of engine revolution and driving force. And CVT can set up a special shift range that obtains not only the engine brake effect but also the maximum speed driving.

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A Study on Development of the Variable Compression Ratio Hydrogen Fueled Engine (가변압축비 수소기관의 개발에 관한 연구)

  • Kim, Sangman;Lee, Jongyun;Lee, Jongtai;Lee, Songyol
    • Transactions of the Korean hydrogen and new energy society
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    • v.4 no.1
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    • pp.1-9
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    • 1993
  • To find performance and knock limit for compression ratio in hydrogen fueled engine, the variable compression ratio hydrogen fueled engine which was able to vary compression ratio during firing was manufactured and estimated. The characteristics of the variable compression ratio hydrogen fueled engine were as follows : 1) compression ratio variation by moving of cylinder head, 2) OHC which can be realized low S/V ratio, short flame propagation distance and unvariable configuration of combustion chamber for compression ratio variation, 3) direct injection of hydrogen gas to restrict back fire.

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Combined Mode I / III Stress Intensity Factor Analysis of a Crack in a Variable Thickness Plate (두께가 변화하는 부재 내의 혼합모드 I / III 균열의 응력확대 계수해석 - 3차원 유한요소해석 중심으로 -)

  • 양원호;최용식;조명래
    • Journal of the korean Society of Automotive Engineers
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    • v.15 no.2
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    • pp.112-120
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    • 1993
  • Variable thickness plates are commonly encountered in the majority of mechanical/structural components of industrial applications. And, as a result of the unsymmetry of the structure or the load and the anisoptropy of the materials, the cracks in engineering structures are generally subjected to combined stresses. In spite of considerable practical interest, however, a few fracture mechanics study on combined mode crack in a variable thickness plate have carried out. In this respect, combined mode 1/3 stress intensity factors $K_{1}$ and $K_{3}$ at the crack tip for a variable thickness plate were obtained by 3-dimensional finite element analysis. Variable thickness plates containing a central slant crack were chosen. the parameters used in this study were dimensionless crack length .lambda. crack slant angle .alpha, thickness ratio .betha. and width ratio .omega. Stress intensity factors were calculated by crack opening displacement(COD) and crack tearing displacement(CTD) method proposed by Ingraffea and Manu. The effect of thickness ratio .betha. on $K_{1}$ is relatively great in comparison to $K_{3}$.

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The Arc Brazing by Variable Polarity AC Pulse MIG Welding Machine (극성가변 AC 펄스 MIG용접기를 이용한 아크 브레이징)

  • 조상명;공현상
    • Journal of Welding and Joining
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    • v.21 no.4
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    • pp.56-62
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    • 2003
  • MIG brazing is used for many parts without melting base metal because of high productivity. Pulsed MIG brazing can be used to further reduce heat input and to improve the process stability. However, a significant amount of zinc in galvanized sheet steel is burned off in the area of brazes. Therefore, the brazing method to reduce the heat input is needed. In the brazing for galvanized sheet steel, variable polarity AC pulse MIG arc brazing can be applied to more decrease the heat input by setting EN-ratio adequately. In this research, we studied for the variable polarity AC pulse MIG arc brazing to decrease the heat input by using ERCuSi-A wire. As the result of increasing EN-ratio, melting ratio of base metal and burning off of zinc were reduced in galvanized sheet steel.