• 에너지공학
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• 제24권4호
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• pp.166-174
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• 2015

본 연구에서는 물성 변화에 따라 자동차 성능 및 환경에 미치는 영향을 살펴보기 위하여 휘발유 대비 물성이 상이한 연료를 선정하여 연소특성을 살펴보았다. 실험은 각 연료에 맞는 점화시기 및 공연비제어를 수행하여 물성변화에 따른 최적의 점화시기와 희박연소에 에서의 연소특성을 살펴보았으며, 그에 따른 배출가스도 평가하였다. 실험을 위해 단기통 엔진을 사용하였으며, 휘발유 물성변화를 위해 "석유 및 석유대체사업법"에 고시된 품질기준을 벗어나는 가짜연료를 선정하여 실험을 수행하였다. 그 결과 선정된 연료의 경우 옥탄가와 증류성상, 증기압에서 차이를 보였으며, 불안정 연소 및 다량의 유해배출가스를 유발함을 알 수 있었다.

• 한국세라믹학회지
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• 제47권1호
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• pp.82-85
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• 2010

Recently, thin film processes for oxides and metal deposition, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), have been widely adapted to fabricate solid oxide fuel cells (SOFCs). In this paper, we presented two research area of the use of such techniques. Gadolinium doped ceria (GDC) showed high ionic conductivity and could guarantee operation at low temperature. But the electron conductivity at low oxygen partial pressure and the weak mechanical property have been significant problems. To solve these issues, we coated GDC electrolyte with a nano scale yittria-doped stabilized zirconium (YSZ) layer via atomic layer deposition (ALD). We expected that the thin YSZ layer could have functions of electron blocking and preventing ceria from the reduction atmosphere. Yittria-doped barium zirconium (BYZ) has several orders higher proton conductivity than oxide ion conductor as YSZ and also has relatively high chemical stability. The fabrication processes of BYZ is very sophisticated, especially the synthesis of thin-film BYZ. We discussed the detailed fabrication processes of BYZ as well as the deposition of electrode. This paper discusses possible cell structure and process flow to accommodate such films.

• 한국세라믹학회지
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• 제45권4호
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• pp.245-249
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• 2008

The SiC and ZrC are critical and essential materials in TRISO coated fuel particles since they act as protective layers against diffusion of metallic and gaseous fission products and provides mechanical strength for the fuel particle. However, SiC and ZrC have critical disadvantage that SiC loses chemical integrity by thermal dissociation at high temperature and mechanical properties of ZrC are weaker than SiC. In order to complement these problems, we made new combinations of the coating layers that the ZrC layers composed of SiC. In this study, after Silicon carbide(SiC) were chemically vapor deposited on graphite substrate, Zirconium carbide(ZrC) were deposited on SiC/graphite substrate by using Zr reaction technology with Zr sponge materials. The different morphologies of sub-deposited SiC layers were correlated with microstructure, chemical composition and mechanical properties of deposited ZrC films. Relationships between deposition pressure and microstructure of deposited ZrC films were discussed. The deposited ZrC films on SiC of faceted structure with smaller grain size has better mechanical properties than deposited ZrC on another structure due to surface growth trend and microstructure of sub-deposited layer.

• The Korean Journal of Ceramics
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• 제5권4호
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• pp.371-374
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• 1999

Y2O3 and Nb2O5 co-doped tetragonal zirconia polycrystals((Y, Nb)-TZP) containing 10 to 30 vol% $Al_2O_3$ were prepared and hydrothermal stability of the composites was evaluated after aging for 5 h at the temperature range of $150^{\circ}C$ $250^{\circ}C$ under 4 MPa $H_2O$ vapor pressure in an autoclave. The (Y, Nb)-TZP/Al2O3 composites showed excellent phase stability under the hydrothermal conditions, as compared with the 3Y-TZP/$Al_2O_3$ composites, due to the combined effects of the Y-Nb ordering in the $t-ZrO_2$ lattice, the reduction of oxygen vacancy concentration, and the $Al_2O_3$ addition. The strength and fracture toughness of the (Y, Nb)-TZP/$Al_2O_3$ composite, containing 20 vol% of 2.8 $Al_2O_3$ particles, were 700 MPa and 8.1 MP.$am^{1/2}$, respectively.

• 대한기계학회논문집A
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• 제39권9호
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• pp.909-916
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• 2015

본 연구는 디젤-과산화수소 에멀젼연료의 충돌분무를 대상으로 과산화수소의 혼합비가 증발분무 거동특성에 미치는 영향을 조사하였다. 에멀젼연료의 증발을 위해 온도조절이 가능한 가열판을 사용하여 온도를 $150^{\circ}C$, $200^{\circ}C$ 및 $250^{\circ}C$로 각각 설정하였고, 연료 분사압력을 400bar, 600bar, 800bar 및 1000bar로 설정하여 분사압력이 에멀젼연료의 증발특성에 미치는 영향을 확인하였다. 에멀젼연료의 혼합을 위 한 계면활성제로 span80과 tween80을 9:1의 비율로 혼합하여 에멀젼연료 전체 체적의 3%로 고정하였고 과산화수소의 혼합비율을 EF(Emulsified Fuel)0, EF2, EF12 및 EF22로 설정하여 디젤연료와 혼합하였다. 또한 에멀젼연료 증발 충돌분무의 가시화를 위해 슐리렌방법을 적용하였다. 본 연구의 결과로서 충돌하는 가열판의 온도와 분사압력이 높을수록 에멀젼연료 증발 촉진으로 연료 기상의 확산이 활발해지는 것을 알 수 있었다. 이러한 결과로부터 실제엔진에 에멀젼연료를 사용할 경우 연료 내 과산화수소 증발에 의한 연소실 온도 저하효과와 함께 보다 신속한 혼합기 형성은 엔진배출물의 감소를 일으키는 것으로 기대된다.

• 한국분말재료학회지
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• 제21권6호
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• pp.434-440
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• 2014

Silicon carbide(SiC) layer is particularly important tri-isotropic (TRISO) coating layers because it acts as a miniature pressure vessel and a diffusion barrier to gaseous and metallic fission products in the TRISO coated particle. The high temperature deposition of SiC layer normally performed at $1500-1650^{\circ}C$ has a negative effect on the property of IPyC layer by increasing its anisotropy. To investigate the feasibility of lower temperature SiC deposition, the influence of deposition temperature on the property of SiC layer are examined in this study. While the SiC layer coated at $1500^{\circ}C$ obtains nearly stoichiometric composition, the composition of the SiC layer coated at $1300-1400^{\circ}C$ shows discrepancy from stoichiometric ratio(1:1). $3-7{\mu}m$ grain size of SiC layer coated at $1500^{\circ}C$ is decreased to sub-micrometer (< $1{\mu}m$) $-2{\mu}m$ grain size when coated at $1400^{\circ}C$, and further decreased to nano grain size when coated at $1300-1350^{\circ}C$. Moreover, the high density of SiC layer (${\geq}3.19g/cm^3$) which is easily obtained at $1500^{\circ}C$ coating is difficult to achieve at lower temperature owing to nano size pores. the density is remarkably decreased with decreasing SiC deposition temperature.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2014년도 제49회 KOSCO SYMPOSIUM 초록집
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• pp.293-294
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• 2014

In Korea, only butane gas could be used as fuel gas of the outdoor gas stove. However, butane is not vaporized well at low temperatures. For this reason, in the field, nozzle of the portable butane gas stove is converted illegally to use propane gas. Because vapor pressure of propane gas is higher than that of butane gas at same temperature, gas accidents such as gas leakage could be occurred. To prevent gas accidents and use portable propane gas stoves safely, international standards need to be analyzed and verification tests need to be performed with prototype stove. This study could suggest to revise standard for safety improvement with portable propane gas stoves.

• 한국안전학회지
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• 제19권2호
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• pp.54-60
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• 2004

Flammable substances are frequently used chemical industry processes. An accurate knowledge of the ALTs(Autoignition Temperatures) is important in developing appropriate prevention and control measures in industrial fire protection. The AITs describe the minimum temperature to which a substance must be heated, without the application of a flame or spark, which will cause that substance to ignite. The AITs are dependent upon many factors, namely initial temperature, pressure, volume, fuel/air stoichiometry, catalyst material, concentration of vapor, ignition delay. This study measured relationship between the AITs and the ignition delay times by using ASTM E659-78 apparatus for methanol and ethanol. The A.A.P.E.(Average Absolute Percent Error) and the A.A.D.(Average Absolute Deviation) of the experimental and the calculated delay times by the AITs for methanol were 14.59 and 1.76 respectively. Also the A.A.P.E. and the A.A.D. of the experimental and the calculated delay times by the ATIs for ethanol were 8.33 and 0.88.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 추계 학술대회논문집
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• pp.179-182
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• 2005

We have developed a numerical scheme to reproduce the unsteady flows with cavitation by the finite-difference method. The evolution of cavitation is represented by the source/sink of vapor phase in the incompressible liquid flow. The pressure-velocity coupling is based on the fractional-step method for incompressible fluid flows, in which the compressibility is taken into account through the low Mach number assumption. We applied our method for the cavitating flows in a two-dimensional cascade, which approximates the portion near the tip of inducer in liquid-fuel engine. Particular attention was focused on the influence of turbulence model in this report. Using an eddy viscosity model, although it was not an optimized one for our purpose, the agreement with the experimental observation was improved.

• 한국안전학회지
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• 제21권4호
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• pp.66-72
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• 2006

An accurate knowledge of the AITs(autoignition temperatures) is important in developing appropriate prevention and control measures in industrial fire protection. The measurement of AITs are dependent upon many factors, namely initial temperature, pressure, vessel size, fuel/air stoichiometry, catalyst, concentration of vapor, ignition delay time. The values of the AITs used process safety are normally the lowest reported, to provide the greatest margin of sefety. This study measured the AITs of o-xylene+n-pentanol system from ignition delay time by using ASTM E659-78 apparatus. The experimental AITs of o-xylene and n-pentanol were $480^{\circ}C\;and\;285^{\circ}C$, respectively. The experiment AITs of o-xylene+n-pentanol system were a good agreement with the calculated AITs by the proposed equations with a few A.A.D.(average absolute deviation).