• 한국수소및신에너지학회논문집
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• 제30권6호
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• pp.531-539
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• 2019

The development of cost-effective electrocatalysts with high durability is one of the most important challenges for the commercialization of polymer electrolyte fuel cells (PEFCs). The durability of the electrocatalyst has been studied in terms of structural change in the active metal and the support. In particular, in fuel cell vehicles, degradation of the carbon-based support is known to have a significant effect on the electrocatalyst deterioration since the start-up/shut-down cycle is frequently repeated. The requirements for the support of the electrocatalyst include high surface area, electrical conductivity, chemical stability, and so on. In this study, we propose the evaluation methods for choosing better support materials and present the physicochemical properties that promising carbon supports should have. Three kinds of carbon materials with different crystallinity are compared. From in-depth study using X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, and accelerated stress test, it is clearly confirmed that the durability of carbon-supported electrocatalysts is closely related to the physicochemical properties of the carbon supports.

• Korean Membrane Journal
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• 제3권1호
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• pp.69-74
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• 2001

Films of TiO$_2$/SiO$_2$ were deposited on the inner surface of the porous glass support tubes by decomposition of tetraisopropyl titanate (TIPT) and tetraethyl orthosilicate (TEOS) at atmospheric pressure. Dense and hydrogen -permselective membranes were formed at 400-600$\^{C}$. The permeation rates of H$_2$ through the membrane at 600$\^{C}$ were 0.2-0.4 ㎤(STP)/min-㎠ atm and H$_2$:N$_2$permeation ratios were above 1000. The permeation properties of the membranes were investigated at various deposition temperatures and TIPT/TEOS concentrations. Decomposition of TIPT alone at temperatures above 400$\^{C}$ produced porous crystalline TiO$_2$ films and they were not H7-selective. Decomposition of TEOS produced H$_2$-permeable SiO$_2$ films at 400-600$\^{C}$ but film deposition rate was very low. Addition of TIFT to the TEOS stream significantly accelerated the deposition rate and produced highly H$_2$-selective films. Increasing the TIPT/TEOS concentration ratio increased the deposition rate. The TiO$_2$/SiO$_2$ membranes formed at 600 $\^{C}$ have the permeation properties comparable to those of SiO$_2$ membranes produced from TEOS.

• 한국추진공학회지
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• 제26권5호
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• pp.24-34
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• 2022

초임계 영역에서 작동하는 탄화수소 연료를 사용하는 재생냉각채널의 냉각성능을 예측하기 위해서는 타당한 물성 예측이 필수이다. 본 연구는 고분자 탄화수소의 임계 압축인자에 따라 밀도와 비열을 적절하게 예측하기 위해 2-파라미터 상태방정식인 SRK(Soave-Redlich-Kwong) 및 PR(Peng-Robinson) 상태방정식과 이를 합한 3-파라미터 상태방정식인 RK-PR 상태방정식에 대한 비교 분석을 수행하였다. 대표적으로 낮은 임계압축 인자를 갖는 n-dodecane 연료와 높은 임계압축 인자를 갖는 JP-10 연료를 선정하여 두 연료의 열역학적 물성을 예측할 때 적합한 상태방정식을 제시하였다. 마지막으로 밀도와 비열의 예측 결과를 NIST REFPROP 데이터와 비교하여 검증하였다.

• Bulletin of the Korean Chemical Society
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• 제35권5호
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• pp.1305-1311
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• 2014

The nickel oxide, the most widely used cathode material for the molten carbonate fuel cell (MCFC), has several disadvantages including NiO dissolution, poor mechanical strength, and corrosion phenomena during MCFC operation. The surface modification of NiO with lanthanum maintains the advantages, such as performance and stability, and suppresses the disadvantages of NiO cathode because the modification results in the formation of $LaNiO_3$ phase which has high conductivity, stability, and catalytic activity. As a result, La-modified NiO cathode shows low NiO dissolution, high degree of lithiation, and mechanical strength, and high cell performance and catalytic activity in comparison with the pristine NiO. These enhanced physico-chemical and electrochemical properties and the durability in marine environment allow MCFC to marine application as a auxiliary propulsion system.

• 대한기계학회논문집B
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• 제27권11호
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• pp.1595-1603
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• 2003

Droplet combustion at high ambient pressures is studied numerically by formulating one dimensional combustion model in the mixture of n-heptane fuel and air. The ambient pressure is supercritical conditions. The modified Soave-Redlich-Kwong state equation is used in the evaluation of thermophysical properties to account for the real gas effect on fluid p-v-T properties in high pressure conditions. Non-ideal thermodynamic and transport property at near critical and supercritical conditions are also considered. Several parametric studies are performed by changing ambient pressure and initial droplet diameter. Droplet lifetime decreased with increasing pressure. Surface temperature increased with increasing pressure. Ignition time increased with increasing initial droplet diameter. Temporal or spatial distribution of mass fraction, mass diffusivity, Lewis number, thermal conductivity, and specific heat were presented.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2002년도 제24회 KOSCO SYMPOSIUM 논문집
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• pp.212-219
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• 2002

Waste fuels, which originate from different sources, have unique combustion characteristics. The characteristics should be considered in applying FBC(fluidized bed combustor) technology to those fuels. The effects of fuel properties and operating conditions on FBC reactivity were investigated by means of carbon based parameter called mean carbon conversion time, rate of carbon conversion, fraction of carbon conversion and carbon recovery. And the basic physical and chemical mechanisms taking place in a fluidized bed were summarized. Major parameters in designing and operating FBC were evaluated in terms of the fuel properties and the combustion environment.

• Tribology and Lubricants
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• 제29권2호
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• pp.117-123
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• 2013

Dimethyl ether (DME) has a high cetane number that is suitable for diesel fuel. DME does not contain sulfur or nitrogen, and is an oxygenated fuel so it produces no particulate matter when combusted and is environmentally friendly. DME fuel for diesel engines show excellent material properties such as a lower volumetric heating value, lower boiling point, lower lubricity, and stronger solvent effect than light oil. This study experimentally examined a lubricity improver (LI) for dimethyl ether. A diesel LI based on biodiesel and fatty acid methyl ester was tested among DME LI candidates. The long-term storage stability and physical properties of the optimum LI for DME were determined.

• Carbon letters
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• 제16권3호
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• pp.198-202
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• 2015

Carbon-supported Pt catalyst systems containing defect adsorption sites on the anode of direct methanol fuel cells were investigated, to elucidate the mechanisms of H₂ dissociation and carbon monoxide (CO) poisoning. Density functional theory calculations were carried out to determine the effect of defect sites located neighboring to or distant from the Pt catalyst on H₂ and CO adsorption properties, based on electronic properties such as adsorption energy and electronic band gap. Interestingly, the presence of neighboring defect sites led to a reduction of H₂ dissociation and CO poisoning due to atomic Pt filling the defect sites. At distant sites, H₂ dissociation was active on Pt, but CO filled the defect sites to form carbon π-π bonds, thus enhancing the oxidation of the carbon surface. It should be noted that defect sites can cause CO poisoning, thereby deactivating the anode gradually.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.478-483
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• 2003

This paper describes spray characteristics of a swirl injector which is intended for use in a HCCI engine. Many optical diagnostics such as laser diffraction methods, and high speed camera photography are applied to measure the spray drop diameter and to investigate the spray development process. The effect of fuel properties on the spray characteristics was investigated using three different fuels because HCCI combustion is tolerant of the chemical composition of various fuels. From these results, the HCCI injector formed a hollow cone sheet spray rather than a liquid jet and the atomization efficiency is high for the low-pressure injector. The SMD of test injector was ranged from $15{\mu}m$ ${\mu}m$ We also found that the spray breakup characteristics were dependent on the fuel properties such as density, viscosity, and surface tension.

• 한국분무공학회지
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• 제14권3호
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• pp.122-130
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• 2009

Vegetable oil and its derivatives as an alternative diesel fuel have become more attractive recently because of its environmental benefits and the fact that they are made from renewable resources. Viscosity is the most significant property to affect the utilization of vegetable oil and its derivatives in the compression ignition engines. This paper presents the existing correlations for predicting the viscosity of vegetable oil and its derivatives for compression ignition engines. According to the parameter considered in the correlations, the empirical correlations can be divided into six groups: correlations as a function of temperature, of proportion, of composition, of temperature and composition, of temperature and proportion, and of fuel properties. Out of physical properties of fuel, there exist in the literature several parameters for giving the influence on kinematic viscosity such as density, specific gravity, the ratio of iodine value over the saponification value, higher heating value, flash point and pressure. The study for the verification of applicability of existing correlations to non-edible vegetable oil and its derivatives is required.