• 대한기계학회논문집B
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• 제35권9호
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• pp.869-874
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• 2011

CNG/diesel dual-fuel 엔진은 CNG 를 주 연료로 사용하고 소량의 디젤을 착화제로서 실린더 내에 분사한다. 본 연구에서는 기존의 디젤엔진을 커먼레일직접분사(CRDI)를 통하여 고압으로 디젤을 분사하고, 예혼합을 위하여 CNG 를 흡기포트에 분사하는 CNG/diesel dual-fuel 엔진으로 개조하였다. CNG/diesel dualfuel engine 은 기존의 디젤엔진과 동등한 수준의 토크 및 출력성능을 나타내었다. 또한, CNG 대체율은 CNG/diesel dual-fuel 엔진의 전체 운전영역에 대하여 89% 이상을 만족시켰다. Dual-fuel 엔진의 PM 배출농도는 디젤엔진보다 94% 더 낮게 나타났지만, NOx 배출농도는 더 높게 나타났다.

• 대한기계학회논문집A
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• 제32권6호
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• pp.465-473
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• 2008

Type II compressed natural gas(CNG) storage vessels for automobiles have been acknowledged for their excellence and have recently become established in local regions. Their supply is not only to automakers in Korea such as Hyundai Motors but they are being increasingly exported. Although the available products have undergone safety evaluations and are certified by an authorized institution they are still short of the optimal design that is possible for such storage vessels. This research investigates the shape and thickness of the dome with the aim of optimizing the type II CNG storage vessels by using a finite element analysis technique. CNG storage vessels can be largely divided into 3 parts namely, the hear part, the cylinder part and the dome part. The head part is designed by means of a hot spinning process and this method is safer than that used in the design of the dome part even though its shape is similar. The thickness of the liners and reinforcing materials was optimized based on the requirements of the cylinder and dome parts. In addition, the shape of the dome, which is most suitable for Type II CNG storage vessels, is proposed by a process of review and analysis of various existing shape, and then conducting a structural stability evaluation to ensure the optimal design plan.

• 전기전자학회논문지
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• 제24권3호
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• pp.821-827
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• 2020

자동차에서 배출되는 배기가스가 대도시의 대기 오염원 중 큰 비중을 차지하고 있다. 특히 디젤이나 CNG버스 등 대중교통의 내연기관 차량은 매일 총 주행거리와 운행시간이 길고 차량 수량이 많기 때문에 배출가스 저감 대책이 시급하다. 본 논문에서는 실제로 전기버스의 도로 주행시험을 통한 연료소모율(km/kWh)을 측정하였다. 측정값을 근거로 버스 한 대당 내연기관과 전기버스에서 발생되는 CO₂배출량을 계산하였다. 전기버스를 시내버스로 대체할 경우 CNG버스 대비 예상되는 이산화탄소 저감 등 환경개선 효과와 더불어 전기버스로 대체가 확대될 경우 부가적인 효과를 분석하였다.

• 한국자동차공학회논문집
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• 제22권2호
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• pp.166-174
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• 2014

Fuel injection pressure has steadily increased in diesel engines for the purpose of improving fuel efficiency and cleaning exhaust gas, but it has now reached a point, where the cost for higher pressure does not warrant additional gains. Common rail systems on modern diesel engines have fuel pumps that are mechanically driven by crankshaft. The pumps actually house two pumping module inside: a low pressure pump component and a high pressure pump component. Part of the fuel compressed by the low pressure component returns to the tank in the process of maintaining the pressure in the common rail. Since the returning fuel represents pumping loss, fuel economy improves if the returned fuel can be eliminated by using a properly controled electrical fuel pump. As the first step in developing an electrical fuel pump the fuel supply system on a 6 liter diesel engine was modeled with AMESim to analyze the workload and the fuel feed rate of the injection pump, and the results served as basis for selecting a suitable servo motor and a reducer to drive the pump. A motor controller was built using a DSP and a program which controls the common rail pressure using a proportional control method based on the target fuel pressure information from the engine ECU. A test rig to evaluate performance of the fuel pump is implemented and used to show that the newly developed electrically driven fuel pump can satisfy the fuel flow demand of the engine under various operating conditions when the rotational speed of the pump is adequately controlled.

• 대한기계학회논문집B
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• 제38권9호
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• pp.731-737
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• 2014

와류실은 압축된 공기를 이용하여 고온과 저온 가스로 분리할 수 있는 단순한 장치로, 차세대 새로운 열교환기로 각광받고 있으나, 와류실 내부에서 발행하는 물리적 유동특성에 대해 아직까지 많이 알려지지 않았다. 본 연구에서는 온도 분리 현상을 조사하기 위해 실험 및 수치해석을 수행하였다. 공급 압력에 따른 온도 변화를 측정하기 위하여 다수의 압력 및 온도 센서를 사용하였으며, CFD 기법을 적용하여 3차원 비정상 압축성 유동장을 조사하였다. 연구를 통해 온도 분리 현상은 점성일과 밀접한 관계가 있는 공급 압력과 와류실의 직경에 영향을 받았으며, 와류실에서 발생하는 온도분리 현상은 압력구배파의 개념으로 확증할 수 없었다.

• 한국치위생학회지
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• 제7권3호
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• pp.213-230
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• 2007

The purpose of this study was to examine the state of infection control provided to members of Korean Dental Hygienists Association. The subjects in this study were dental hygienists who attended a symposium on July 1. 2006. after a survey was conducted, the answer sheets from 489 participants were analyzed, and the findings of the study were as follows: 1. Possession of disinfection room was being(72.7%), and person of infection control was zero(52.9%). Number of sterilizer was one(62.2%). 2. As a repetition choice, type of sterilizer was autoclave(97.9%), UV sterilizer(67.4%) and EO gas sterilizer(21.4%). As a repetition choice, infection materials was ethanol(84.1%). 3. Water tube of unit and chair was using of sterilized water(42.9%). Sterilizing of compressed air was no(69.0%). 4. Re-using of disposal was not using(62.5%), re-using disposal was suction tip(28.2%)(repetition choice) 5. In sterilization of instruments, hand-piece was every using time(28.4%), and reamer-file, bur, mirror, pincette, explorer, hand scaler and ultrasonic scaler were high in every using time. 6. Individual protection was high of using, cleaning of hands before treatment was every treatment(87.0%). Type of soap was liquid type in dental clinic(48.2%), infection soap in dental hospital(41.2%) and solid soap in public health center(50.6%). Answered that they need regular oral health education, and 82.9% respondents answered that they need oral health technicians in school. And 87.8% respondents needed individual oral health education for the benefit of better oral health.

• 한국추진공학회지
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• 제16권6호
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• pp.79-84
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• 2012

창이 있고 밀폐되어있는 시험챔버를 사용하여 고속가압에 의한 고체추진제의 균열진전시험을 수행하였다. 고체추진제 예균열 시험편은 시험챔버내에 설치되고, 축압기 내에 고압으로 축적된 질소가스는 고속가압을 위해 가압밸브를 통해 시험챔버를 가압한다. 시험챔버 내의 압력이 설정압력에 도달하게 되면 가압밸브는 닫히고 배기밸브를 통해 시험챔버는 감압이 된다. 본 논문에서는 시험결과로부터 시간에 따른 시험챔버압력을 나타내는 압력-시간 선도를 얻었으며, 선도로부터 가압비(${\Delta}P/{\Delta}t$)를 계산하였다. 3가지 가압비 64.34, 73.86, 85.44 MPa/s 에 대한 시험을 수행하였으며, 가압비에 따른 균열진전 길이를 측정하였다. 또한 고속 디지털카메라촬영을 통해 균열진전과정을 분석하였다.

• 대한조선학회논문집
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• 제57권4호
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• pp.213-220
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• 2020

In the present paper, implosion responses of two adjacent cylindrical tubes under external hydrostatic pressure were experimentally investigated. The cylinder models were fabricated of aluminium alloy 6061-T6 commercial tubes. In the experiment, a pair of two-cylinders were placed inside of a support frame in a medium-size pressure chamber, whose design pressure was 6.0MPa. The distance between the two-cylinders was 30 millimeter measured from outer shell at the mid-length. The implosion tests were performed with water and compressed nitrogen gas as the pressurizing media. The ambient static pressure of the chamber and local dynamic pressure near the two-imploded models were measured simultaneously. It was found that the energy released during an implosion from the first, weaker cylinder triggered the instability of the second, stronger cylinders. In other words, the resulting shock wave of the first implosive impact from the weaker cylinder could cause the premature failure of the neighboring stronger cylinders. The non-contact implosion phenomena from the two-cylindrical tube were clearly observed.

• 한국임상수의학회지
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• 제35권3호
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• pp.114-118
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• 2018

A 3-month-old intact male Lakeland terrier was presented with recurring regurgitation after removing cervical esophageal foreign body by endoscopy. Blood and urine analysis, radiography, ultrasonography, fluoroscopic esophagography, computed tomographic angiography (CTA) were performed. In radiography and fluoroscopic esophagography, vascular ring anomaly was considered as the primary cause of megaesophagus, and CTA with gas-inflation of the esophagus was performed. Compressed esophagus, persistent right aortic arch (PRAA), aberrant left subclavian artery (LSA), and a venous structure which was confirmed in surgery to be incomplete type persistent left cranial vena cava (PLCVC) connected with the left side azygos vein were observed. Left deviation of the trachea was also revealed in CT, which implies the compression by left ligamentum arteriosum. Therefore, type 3 PRAA with left ligamentum arteriosum and aberrant LSA, was considered as a prior differential diagnosis. Surgical repair was performed and the clinical signs improved. This report describes CTA characteristics of combination of PRAA with aberrant LSA, incomplete PLCVC and Lt. azygos vein in a dog. Although not every vascular anomaly does induce clinical sign, some types can complicate the surgical procedure, and cause clinical signs. Therefore, thorough evaluation of vascular anomalies in the thorax is important, and CTA is a useful method in identifying multiple vascular anomalies in dogs.

• 한국수소및신에너지학회논문집
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• 제27권6호
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• pp.642-650
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• 2016

One of the most feasible solution for reducing the excessive energy consumption and carbon dioxide emission is usage of more efficient fuel such as hydrogen. As is well known, there are three viable technologies for storing hydrogen fuel: compressed gas, metal hydride absorption, and cryogenic liquid. In these technologies, the storage for liquid hydrogen has better energy density by weight than other storage methods. However, the cryogenic liquid storage has a significant disadvantage of boiling losses. That is, high performance of thermal insulation systems must be studied for reducing the boiling losses. This paper presents an experimental study on the effective thermal conductivities of the composite layered insulation with aerogel blankets($Cryogel^{(R)}$ Z and $Pyrogel^{(R)}$ XT-E) and Multi-layer insulation(MLI). The aerogel blankets are known as high porous materials and the good insulators within a soft vacuum range($10^{-3}{\sim}1$ Torr). Also, MLI is known as the best insulator within a high vacuum range(<$10^{-6}{\sim}10^{-3}$ Torr). A vertical axial cryogenic experimental apparatus was designed to investigate the thermal performance of the composite layered insulators under cryogenic conditions as well as consist of a cold mass tank, a heat absorber, annular vacuum space, and an insulators space. The composite insulators were laminated in the insulator space that height was 50 mm. In this study, the effective thermal conductivities of the materials were evaluated by measuring boil-off rate of liquid nitrogen and liquid argon in the cold mass tank.