• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.2
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• pp.121-126
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• 2006

A gasoline-fueled stratified charge compression ignition (SCCI) engine with both direct fuel injection and intake temperature and compression ratio was examined. The fuel was injected directly by using the high temperature resulting from heating intake port. With this injection strategy, the SCCI combustion region was expanded dramatically without any increase in NOx emissions which were seen in the case of compression stroke injection. Injection timing during the intake temperature was found to be an important parameter that affects the SCCI region width. The effect of mixture stratification and the effect of fuel reformation can be utilized to reduce the required intake temperature for suitable SCCI combustion under each set of engine speed and compression ratio conditions.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.454-454
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• 2013

태양전지는 화석연료의 고갈로 인해 새로운 대체 에너지원으로 관심을 받고 있다. 유기태양전지는 무기물 태양전지와 비교하여 제작 단가가 낮은 경제성과 다양한 기판을 사용할 수 있는 다양한 응용성을 가지고 있기 때문에 많은 관심을 받고 있다. 실리콘 기반의 태양전지에 비해서 유기태양전지의 효율이 낮은 단점을 가지고 있기 때문에 효율을 높이기 위한 다양한 연구가 진행되고 있다. 광활성층에서 생성되는 전자-홀 쌍을 효율적으로 분리하여 손실되는 전하를 줄여서 효율을 높이는 방법이 활발히 연구되고 있다. 본 연구에서는 초음파 처리 시간에 따라 나노구조를 가지는 고분자 광활성층의 표면거칠기가 변화하여 유기 태양전지의 전력변환 효율에 미치는 영향을 조사하였다. 전자주게 물질인 P3HT를 용매에 녹여서 스핀코팅 한 후 초음파 처리를 하여 나노 구조를 형성하였고, 초음파 처리 시간에 따라서 형성한 나노 구조의 구조적 및 광학적 특성 변화를 광류미네센스와 원자힘 현미경 측정으로 관찰하였다. 전류밀도-전압 측정 결과는 초음파 처리 시간을 최적화하면 P3HT 나노 입자의 크기가 가장 작게 형성되어 계면 면적을 가장 크게 증가시켜 전자-홀 쌍을 효율적으로 분리하여 전력변환 효율이 증가하는 것을 확인 하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.3
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• pp.221-228
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• 2013

An experimental study was carried out to investigate the effects of the injection timing on the spray and combustion characteristics in a spray-guided direct-injection spark-ignition (DISI) engine under lean stratified operation. An in-cylinder pressure analysis, exhaust emissions measurement, and visualization of the spray and combustion were employed in this study. The combustion in a stratified DISI engine was found to have both lean premixed and diffusion controlled flame combustion characteristics. The injection timing condition corresponding to the stratified mixture characteristics was verified to be a dominant factor for these flame characteristics. For the early injection timing, a non-luminous blue flame and low combustion efficiency were observed as a result of the lean homogeneous mixture formation. On the other hand, a luminous sooting flame was shown at the late injection timing because of an under-mixed mixture formation. In addition, the smoke emission and incomplete combustion products were increased at the late injection timing as a result of the increased locally rich area. On the other hand, the NOx emissions decreased and IMEP increased as the injection timing retarded. The combustion phasing produced by the injection timing was verified as the reason for this observation.

• Solar Energy
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• v.11 no.3
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• pp.44-52
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• 1991

The benefits of thermal stratification in sensible heat storage systems has been considered and studying by several investigators. In this paper, the basic data which is hard to obtain normally through the experiment were obtainable through the computer simulation. The major objectives of the study were to assess the benefits of stratified storage in residential solar water heating application and to suggest the optimum design parameters. From the computer simulation, following results were obtained. 1. The solar load fraction increases with increasing the number of tank segments. In these simulation, the magnitude of the improvement was about 10%. 2. The solar load fraction increases when the ratio of diameter to height of the tank(H/D) increases to 3, but H/D exceed 3 then, the solar load fraction decreases. In these simulation, the magnitude of the improvement was about 3%. 3. Increasing the collector flow rate slightly improved the performance of the mixed storage system(Node=1). But, for the stratified storage system(Node=N), the solar load fraction increases with decreasing flow rate until the point is reached at which the collector outlet temperature reaches the boiloff limit of $100^{\circ}C$ over some portion of the simulation period.

• Journal of the Korean earth science society
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• v.37 no.7
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• pp.465-475
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• 2016

The diurnal and semidiurnal tides in the global atmosphere are examined using 3-hourly geopotential height field of the state-of-the-art reanalysis data. Unlike the previous studies, the spatial structure and seasonality of those tides are analyzed from the surface of the earth to the stratosphere. It is found that, at most levels, diurnal tide is strong in the midlatitudes while semidiurnal tide is predominant in the tropics. The former shows strong seasonal cycle with a larger amplitude in summer than in winter in both hemispheres. This is different from the semidiurnal tide which has essentially no seasonal cycle. In term of the vertical structure, while semidiurnal tide has a barotropic structure, diurnal tide exhibits a distinct vertical structure with increased amplitude and height. Especially tropical diurnal tide exhibits a nearly opposite phase from the surface to the free troposphere, and to the upper stratosphere. Its amplitude also varies nonlinearly with height, possibly influenced by water vapor, ozone, gravity waves and solar radiation.

• Aerospace Industry
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• v.69
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• pp.44-47
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• 1999

사람은 자신의 이동에 기계를 사용하기 시작했고 그 발전속도는 항공기의 발달로 극에 달한 느낌이다. 그러나 이러한 이동수단은 필연적으로 사고를 동반하는 것 또한 현실이다. 각종 이동수단 즉 교통수단 가운데서 사고 발생률의 면에서는 단연 항공기가 가장 낮다고 하지만 항공기 사고는 한번 나면 대형사고이고 인명의 살상이 많기 마련이다. 항공기 사고는 오늘날 사고 내용을 자세히 살펴보면 고정익기 보다는 회전익이 더 많고 성층권을 비행할 때 보다는 대기권을 운행할 때가 더 많다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.26 no.4
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• pp.353-359
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• 1990

Chinhae Bay, included small ports, is the region which the red tide phenomenon is occurred frequently in summer season. Field sampling of 4 cross-sections in the bay resulted in detailed informations on cross-sectional velocity distributions, salt concentrations and discharge during one consecutive tidal cycle in summer season, 1983. High velocity cores reoccur two times a semi-diurnal tidal cycle at the same cross-sectional location, lower layer, in Kadok Channel during the spring tide. The tidal exchange ratio was estimated by Eulerian method. The range of exchange ratios in central Kadok Channel are 9.3-17% at the spring tide and 16.9-21.8% at the neap tide. On the other hand, its range in Masan bay-mouth is 8.7% at the spring tide and 2.0% neap tide, respectively.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.3
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• pp.7-12
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• 2003

Mixture formation in the cylinder of a lean bum engine has been observed by Laser Induced Fluorescence technique. XeCl laser (308nm) was used to produce a laser sheet. 3-pentanone has been added to iso-octane fuel to produce fluorescence, the intensity of which is proportional to the concentration of the fuel. The laser sheet was introduced through the piston window and the fuel distribution in the vertical plane was observed through a side window. Comparison has been made for the cases of selected fuel injection timing as 0, 360, 405, and 450 CA. For the case of 0 and 360 CA injection, uniform fuel distribution in the combustion chamber has been obtained at the ignition time which is favorable for the high load mode. And the late injection cases, 405 and 450 CA, revealed the stratified formation of rich mixture around the spark plug. That extends the lean misfire limit and reduces cyclic variation in the low load mode.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.5
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• pp.86-96
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• 2007

A direct-injection stratified-charge(DISC) engine has been considered as a promising alternative in spite of high unburned hydrocarbon emission levels during light load operation. In this paper investigation is made to characterize formation and combustion processes of stratified mixture charge in a simple constant volume combustion chamber. Both experimental and numerical analyses are performed for fluid and combustion characteristics with 3 different induction types for rich, homogeneous and lean mixture conditions. The commercial code FIRE is applied to the turbulent combustion process in terms of measured and calculated pressure traces and calculated distributions of mean temperature, OH radical and reaction rate. It turns out that the highest combustion rate occurs for the rich state condition at the spark ignition location due to existence of stoichiometric mixture and timing.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.2064-2070
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• 1995

Characteristics of thermal flow stratification were studied experimentally by using the small scale pressurizer-surge line model. Thermal flow stratifications in the horizontal section of surge line were analyzed by the relation between the maximum temperature difference at any cross section in surge line and the Froude number representing the boundary conditions, i.e., in/out surge flow velocity and temperature difference of system. Thermal flow stratifications in outsurge flow decreased inversely proportional to the Froude number and did not exist for Fr>1. In insurge flow thermal flow stratifications disappeared near Fr=1.5, but resulted in the higher temperature difference than the case of outsurge flow.