• 한국연소학회지
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• 제18권4호
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• pp.12-20
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• 2013

The ignition delay time is an important factor to understand the combustion characteristics of internal combustion engine. In this study, ignition delay times of cool and thermal flame were observed separately in homogeneous charge compression ignition(HCCI) engine. This study presents numerical investigation of ignition delay time of n-heptane and alcohol(ethanol and n-butanol) binary fuel. The $O_2$ concentration in the mixture was set 9-10% to simulate high exhaust gas recirculation(EGR) rate condition. The numerical study on the ignition delay time was performed using CHEMKIN codes with various blending ratios and EGR rates. The results revealed that the ignition delay time increased with increasing the alcohol fraction in the mixture due to a decrease of oxidation of n-heptane at the low temperature. From the numerical analysis, ethanol needed more radical and higher temperature than n-butanol for oxidation. In addition, thermal ignition delay time is sharply increasing with decreasing $O_2$ fraction, but cool flame ignition delay time changes negligibly for both binary fuels. Also, in high temperature regime, the ignition delay time showed similar tendency with both blends regardless of blending ratio and EGR rate.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.379-381
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• 2009

The simulation model for metal-supported Solid Oxide Fuel Cell(SOFC) is developed in this study. Open circuit voltage is calculated using Nernst equation and Gibbs free energy is required by thermodynamic. The exchange current densities are compared with experimental results since exchange current density is most effective factor for the activation loss. Liu's study is used for the exchange current density of cathode, BSCF, and Koide's result is applied for the exchange current density of anode, Ni/YSZ. For the ohmic loss, ionic conductivity of YSZ is described from Kilner's mode and the data are compared with Wanzenberg's experimental data. Diffusivity is an important factor for the mass transfer through the porous medium. Both binary diffusion and Knudsen diffusion are considered as the diffusion mechanism. For validation, simulation results at this work are compared with our experimental results.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 추계학술대회 논문집
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• pp.63-66
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• 2008

This study presents 0-dimensional model for solid oxide fuel cells(SOFCs). The physics of the cell and the simplifying assumptions are presented, and only hydrogen participates in the electrochemical reaction. The electrical potential is predicted using this model. The Butler-Volmer equation is used to describe the activation polarization and the exchange current density is changed according to the partial pressure of reactants and the temperature. The electrical conductivities of electrodes and an electrolyte are calculated for the ohmic polarization. Material characteristics and temperature affect those factors. Analysis of concentration polarization based on transport of gaseous species through porous electrodes is incorporated in this model. Both binary diffusion and Knudsen diffusion are considered as the diffusion mechanism. For validation, simulation results at this work are compared with our experimental results and numerical results by other researchers.

• 한국세라믹학회지
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• 제36권4호
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• pp.360-365
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• 1999

The combustion process was applied to synthesize the LiAlO2 powder with high specific surface area and pure crystalline ${\gamma}$-phase. For the combustion synthesis of LiAlO2 which is a binary-component oxide in-cluding lithium and aluminum ions the mixture of citric acid and urea with stoichiometric composition was selected as a promising fuel. The highest combustion temperature was measured in the reaction using the mixed fuel with a stoichiometric composition. The synthesized powder was very fine and its specific surface area was more than 15 m2/g.

• 멤브레인
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• 제27권1호
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• pp.53-59
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• 2017

본 연구에서는 고분자전해질 연료전지(PEMFC)의 전해질막의 성능향상을 위하여 sulfonated graphene oxide(sGO)와 Nafion을 이용하여 복합막을 개발하였다. sGO/Nafion 복합막 안의 sGO의 균일한 분산을 위해 각기 다른 용매를 사용한 sGO 분산액과 Nafion 현탁액을 혼합하여 복합막들을 제조하였다. 제조된 복합막들의 물성 및 전기화학적 특성을 평가하기 위해 SEM, FT-IR, 이온 전도도, 이온 교환 용량, 함수율, 열안정성 등을 수행하였다. 연구 결과 ODB와 DMAc 혼합 용매로 sGO를 분산하여 고분자 용액 내에서의 분산도를 향상시켰으며, 이 결과 11 wt%의 낮은 함수율에도 불구하고, $0.06Scm^{-1}$의 기존 연구와 유사한 이온 전도도를 나타내었다.

• 방사성폐기물학회지
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• 제19권3호
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• pp.353-366
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• 2021

The solubilities of different multicomponent lanthanide oxide (Ln₂O₃) solid solutions including binary (Ln₁ and Ln₂ = La, Nd, Eu, or Tm), ternary (Ln₁, Ln₂, and Ln₃ = La, Nd, Eu, or Tm), and higher systems (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) were studied after aging for four weeks at 60℃. Our recent study revealed that the phase transformations in binary ((La, Nd) and (La, Eu)) and ternary (La, Nd, Eu) systems are responsible for the formation of (La, Nd)(OH)₃, (La, Eu)(OH)₃, and (La, Nd, Eu)(OH)₃ solid solutions, respectively. The variations in the mole fractions of La³⁺, Nd³⁺, and Eu³⁺ in the sample solutions of these hydroxide solid solutions indicated that a thermodynamic equilibrium might account for the apparent La, Nd, and Eu solubilities. Conversely, the binary and ternary systems containing Tm₂O₃ as the heavy lanthanide oxide retained the oxide-based solid solutions, and their solubility behaviors were dominated by their congruent dissolutions. In the higher multicomponent system, the X-ray diffraction patterns of the solid phases, before and after contact with the aqueous phase indicated the formation of a stable oxide solid solution and their solubility behavior was explained by its congruent dissolution.

• Nuclear Engineering and Technology
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• 제56권5호
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• pp.1672-1678
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• 2024

We introduce a creative approach combining machine learning with optimization techniques to enhance the optimization of the loading pattern (LP). Finding the optimal LP is a critical decision that impacts both the reload safety and the economic feasibility of the nuclear fuel cycle. While simulated annealing (SA) is a widely accepted technique to solve the LP optimization problem, it suffers from the drawback of high computational cost since LP optimization requires three-dimensional depletion calculations. In this note, we introduce a technique to tackle this issue by leveraging neural networks to filter out inappropriate patterns, thereby reducing the number of SA evaluations. We demonstrate the efficacy of our novel approach by constructing a machine learning-based optimization model for the LP data of the Korea Standard Nuclear Power Plant (OPR-1000).

• Tribology and Lubricants
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• 제38권4호
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• pp.136-142
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• 2022

This paper investigates the enhanced wear performance of a CrAl coated accident tolerant fuel (ATF) cladding. In the wake of the Fukushima accident, extensive research on ATF with respect to improving the oxidation resistance of cladding materials is ongoing. Since coated Zr claddings can be applied without major changes to the criteria for reactor core design, many researchers are studying coatings for claddings. To improve the quality of the CrAl coating layer, optimization of the manufacturing process is imperative. This study employs arc ion plating to obtain improved CrAl coated claddings using CrAl binary alloy targets through an improved coating method. Surface roughness and adhesion are improved, and droplets are reduced. Furthermore, the coated layer has a dense and fine microstructure. In scratch tests, all the tested CrAl coated claddings exhibit a superior resistance compared to the Zr cladding. In a fretting wear test, the wear volume of the CrAl coated claddings is smaller compared to the Zr cladding. Furthermore, the coated cladding manufactured through the improved process exhibits better wear resistance than other CrAl coated claddings. Based on these results, we suggest that fine microstructure is attributed to a mechanically and microstructurally robust CrAl coating layer, which enhances wear resistance.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2012년도 춘계학술발표대회
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• pp.71.1-71.1
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• 2012

Proton Exchange Membrane Fuel Cells (PEMFCs) have been of great interest particularly in the automobile industries because of their high energy density and low pollutant emission. However, some of the issues such as, the necessarily high contents of Pt catalysts and their slow kinetics of cathode oxygen reduction reaction remain as obstacles in the commercialization of the PEMFC. In this presentation, after brief explanation on basic principles of PEMFC and its application to FC vehicles, recent researches to improve the activity and durability of Pt-based nano catalysts toward oxygen reduction will be introduced. It covers size and shape control of Pt nano particle, binary and ternary Pt-M alloys, novel core-shell nano structures of Pt, and a little bit about non-Pt catalysts. Strategies and methodologies for design and synthesis of novel catalysts will also be included.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
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• pp.209-211
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• 2015

Evaporation characteristics of a single droplet of carbon nanofluids were investigated in a rapid compression machine(RCM). n-Heptane and carbon black N990 were used to synthesize the carbon nanofluids. RCM is an experimental set-up to simulate a single compression stroke of reciprocating engine. Temperature and pressure in a reaction chamber were measured during the compression stroke. After the piston reaches top dead center(TDC), temperature and pressure decreased due to the heat loss at wall. In that process, a single droplet of carbon nanofluids underwent unsteady condition. A single droplet was put at the center of reaction chamber. Thermocouple whose tip is $50{\mu}m$ was used not only to measure transient bulk temperature, but also to suspend the droplet. The picture of single droplet was taken using high speed camera with a frame rate of 500 fps. From those pictures, the droplet diameter was measured by visual basic program.