• Tribology and Lubricants
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• 제14권4호
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• pp.108-113
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• 1998

In order to investigate the characteristics of top ring groove deposit formation in diesel engine, engine test and simulation test were performed. From component analysis of used oils sampled from actual running engines, soot content in engine oil was selected as a main parameter for evaluating oil degradation. Deposit formation is highly related to soot content in lubricating oils. And high soot content oil accelerates deposit formation even in low temperature region below 26$0^{\circ}C$. In low temperature region below 26$0^{\circ}C$, deposit formation rate is mainly affected by top ring groove temperature. However, in high temperature region above 26$0^{\circ}C$, deposit formation rate is affected by soot content as well as top ring groove temperature. Therefore, soot content as well as top ring groove temperature should be kept a certain level in order to prevent troubles due to carbon deposit formation.

• 공업화학
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• 제29권5호
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• pp.626-629
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• 2018

연료전지는 높은 연료유연성을 갖고 있어, 탄소 및 탄화수소 등을 통해서도 전기를 생산할 수 있다. 하지만 이러한 연료원을 사용한 경우, 불안정한 장기 구동성능이 종종 관측된다. 본 연구에서는 반응기 내부에 존재하는 탄화수소가 장기 구동성능을 불안정하게 함을 밝힌다. 본 연구진은 비활성기체인 아르곤을 이용하여 산화극 반응기 내부의 가스화경로를 예측하고, 이를 통해 탄화수소의 영향을 억제하여 불안정한 장기 구동성능을 극복한다. 더 나아가, 산화극 반응기 내부에 이산화탄소를 공급하여 역부드아반응을 유도한다. 역부드아반응을 통해 탄소연료전지에서 연료로 사용될 수 있는 일산화탄소를 만들어낸다. 과도한 이산화탄소의 주입은 오히려 연료손실 등의 문제를 야기함을 확인한다. 따라서, 본 연구에서는 이산화탄소 공급량의 최적화가 중요함을 밝히고, 이를 통해 연료전지 구동 성능을 안정화한다.

• Corrosion Science and Technology
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• 제7권2호
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• pp.69-76
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• 2008

Common methods for large scale hydrogen production, such as steam reforming and coal gasification, also involve production of carbonaceous gases. It is therefore necessary to handle process gas streams involving various mixtures of hydrocarbons, $H_2$, $H_2O$, CO and $CO_2$ at moderate to high temperatures. These gases pose a variety of corrosion threats to the alloys used in plant construction. Carbon is a particularly aggressive corrodent, leading to carburisation and, at high carbon activities, to metal dusting. The behaviour of commercial heat resisting alloys 602CA and 800, together with that of 304 stainless steel, was studied during thermal cycling in $CO/CO_2$ at $650-750^{\circ}C$, and also in $CO/H_2/H_2O$ at $680^{\circ}C$. Thermal cycling caused repeated scale separation, which accelerated chromium depletion from the alloy subsurface regions. The $CO/H_2/H_2O$ gas, with $a_C=2.9$ and $p(O_2)=5\times10^{-23}$ atm, caused relatively rapid metal dusting, accompanied by some internal carburisation. In contrast, the $CO/CO_2$ gas, with $a_C=7$ and $p(O_2)=10^{-23}-10^{-24}$ atm caused internal precipitation in all three alloys, but no dusting. Inward diffusion of oxygen led to in situ oxidation of internal carbides. The very different reaction morphologies produced by the two gas mixtures are discussed in terms of competing gas-alloy reaction steps.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.306-309
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• 2005

One of the most critical issues in sol id oxide fuel cell (SOFC)running on hydrocarbon fuels is the risk of carbon formation from the fuel gas. The simple method to reduce the risk of carbon formation from the reactions is to add steam to the fuel stream, leading to the carbon gasification react ion. However, the addition of steam to fuel is not appropriate for the auxiliary power unit (APU) and potable power generation (PPG) systems due to an increase of complexity and bulkiness. In this regard, many researchers have focused on so-called 'direct methane' operation of SOFC, which works with dry methane without coking. However, coking can be suppressed only by the operation with a high current density, which may be a drawback especially for the APU and PPG systems. The single chamber fuel cell (SC-SOFC) is a novel simplification of the conventional SOFC into which a premixed fuel/air mixture is introduced. It relies on the selectivity of the anode and cathode catalysts to generate a chemical potential gradient across the cell. Moreover it allows compact and seal-free stack design. In this study, we fabricated honeycomb type mixed-gas fuel cell (MGFC) which has advantages of stacking to the axial direction and increasing volume power density. Honeycomb-structured SOFC with four channels was prepared by dry pressing method. Two alternative channels were coated with electrolyte and cathode slurry in order to make cathodic reaction sites. We will discuss that the anode supported honeycomb type cell running on mixed gas condition.

• 한국세라믹학회지
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• 제42권12호
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• pp.860-864
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• 2005

In this study, we fabricated honeycomb type Mixed-Gas Fuel Cell (MGFC) which has advantages of stacking to the axial direction and increasing volume power density. Honeycomb-shaped anode with four channels was prepared by dry pressing method. Two alternative channels were coated with electrolyte and cathode slurry in order to make cathodic reaction sites and the others were filled with partial oxidation (POX) catalyst to increase fuel conversion. Furthermore we employed the sol-gel technique which can increase cell performance and decrease carbon coking.

• 항공우주시스템공학회지
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• 제14권4호
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• pp.32-39
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• 2020

A technological review and analysis were performed on thermal cracking of aviation hydrocarbon fuels that circulate as coolants in regenerative cooling systems of hypersonic flights. Liquid hydrocarbons decompose into low-carbon-number hydrocarbons when they absorb a considerable amount of energy at extremely high temperatures, and these thermal cracking behaviors are represented by heat sink capacity, conversion ratio, reaction products, and coking propensity. These parameters are closely interrelated, and thus, they must be considered for optimum performance in terms of the overall heat absorption in the regenerative cooling system and supersonic combustion in the scramjet engine.

• 공업화학
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• 제32권1호
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• pp.83-90
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• 2021

본 연구에서는 저온 열처리 탄소의 물리·화학적 특성이 이차전지 음극재로서의 전기화학적 거동에 미치는 영향에 대하여 고찰하였다. 석유계 핏치의 코크스화를 위하여 600 ℃ 열처리를 수행하였으며 제조된 코크스는 700~1500 ℃로 탄화 온도를 달리하여 저온 열처리 탄소 음극재로 제조되었다. 탄소 음극재의 물리 화학적 특성은 N2 흡·탈착 등온선, X-ray diffraction (XRD), 라만 분광(Raman spectroscopy), 원소 분석 등을 통하여 확인하였으며,저온 열처리 탄소의 음극 특성은 반쪽 전지를 통한 용량, 초기 쿨롱 효율(ICE, initial Coulomb efficiency), 율속, 수명 등의 전기화학적 특성을 통하여 고찰하였다. 저온 열처리 탄소의 결정 구조는 1500 ℃ 이하에서 결정자의 크기와 진밀도가 증가하였으며 비표면적은 감소하였다. 저온 열처리 탄소의 물리화학적 특성 변화에 따라 음극재의 전기화학 특성이 변화하였는데 수명 특성은 H/C 원소 비, 초기 쿨롱 효율은 비표면적, 율속 특성은 진밀도의 특성에 기인하는 것으로 판단되었다.

• Korean Chemical Engineering Research
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• 제56권2호
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• pp.176-185
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• 2018

지구 온난화가 가속화됨에 따라 온실가스 감축이 보다 중요해졌다. 이산화탄소 건식 개질은 온실가스인 $CO_2$와 $CH_4$를 활용하여 부가가치가 높은 물질인 CO와 $H_2$를 얻을 수 있는 유망한 온실가스 감축 기술이다. 그러나 이 반응이 일어나는 반응기의 운전 중에 심각한 코킹 문제가 발생할 수 있다. 이산화탄소 개질반응은 매우 강한 흡열반응이기 때문에 반응기 입구 근처에서 반응 온도가 많이 떨어지면서 코크 생성을 야기시킨다. 이러한 문제를 해결하기 위해서는 코크 생성이 잘 일어나지 않는 온도영역에서 반응이 일어나도록 하는 것이 중요하다. 본 연구에서는 새로운 촉매 배열 방법을 이용하여 반응기 전 구간이 코크 생성이 잘 일어나지 않는 온도 영역 내에서 유지되도록 하는 설계 방법을 제안하였다. 이 설계 방법은 연료 유량, 촉매 밀도, 구간 별 출구 온도를 최적화 변수로 하여 주어진 전환율에 대하여 반응기 길이를 최소화 할 수 있는 최적화 문제를 풀도록 하여 반응기를 최적화한다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.115.2-115.2
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• 2010

Autothermal reforming(ATR) processes of hydrocarbon liquids such as diesel fuels are spotlighted as methods to produce hydrogen for Fuel cell. However, the use of heavy hydrocarbons as feedstocks for hydrogen production causes some problems which increase the catalyst deactivation by the carbon deposition. Coking can be inhibited by increasing the water dissociation on the catalyst surface. This results in catastrophic failure of whole system. Performance degradation of diesel autothermal reforming leads to increase of undesirable hydrocarbons at reformed gases and subsequently decrease the performance. In this study, perovskite-based catalysts were investigated as alternatives to substitute the noble metal catalyst for the ATR of diesel. The investigated perovskite structure was based on LaCrO3. and metals were added at the A-site to enhance oxygen ion mobility, transition metals were doped on the B-site to enhance the reformation. Substituted Lanthanum chromium perovskite were made by aqueous combustion synthesis, which can produce high surface area. And for the homogeneous fuel supply, we made ultrasonic injection system for reforming. We compared durability of evaporation system and ultrasonic system for fuel injection.

• 한국수소및신에너지학회논문집
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• 제29권6호
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• pp.559-569
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• 2018

Catalytic supports made of carbon have many advantages, such as high coking resistance, tailorable pore and surface structures, and ease of recycling of waste catalysts. Moreover, they do not require pre-reduction. In this study, ash-free coal (AFC) was obtained by the thermal extraction of carbonaceous components from raw coal and its performance as a carbon catalytic support was compared with that of well-known activated carbon (AC). Nickel was dispersed on the carbon supports and the resulting catalysts were applied to the steam reforming of toluene (SRT), a model compound of biomass tar. Interestingly, nickel catalysts dispersed on AFC, which has a very small surface area (${\sim}0.13m^2/g$), showed higher activity than those dispersed on AC, which has a large surface area ($1,173A/cm^2$). X-ray diffraction (XRD) analysis showed that the particle size of nickel deposited on AFC was smaller than that deposited on AC, with the average values on AFC ${\approx}11nm$ and on AC ${\approx}23nm$. This proved that heteroatomic functional groups in AFC, such as carboxyls, can provide ion-exchange or adsorption sites for the nano-scale dispersion of nickel. In addition, the pore structure, surface morphology, chemical composition, and chemical state of the prepared catalysts were analyzed using Brunauer-Emmett-Taylor (BET) analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM), x-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, and temperature-programmed reduction (TPR).