• Korean Journal of Metals and Materials
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• v.46 no.5
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• pp.321-327
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• 2008

Cu based amorphous ($Cu_{54}Zr_{22}Ti_{18}Ni_6$) coating was produced by cold spraying as a new fabrication process. The microstructure and macroscopic properties of amorphous coating layer was investigated and compared with those of cold sprayed pure Cu coating. Amorphous powders were prepared by gas atomization and Al 6061 was used as the substrate plate. X-ray diffraction results showed that Cu based amorphous powder could be successfully deposited by cold spraying without any crystallization. The Cu based amorphous coating layer ($300{\sim}400{\mu}m$ thickness) contained 4.87% porosity. The hardness of Cu based amorphous coating represented $412.8H_v$, which was correspond to 68% of the hardness of injection casted bulk amorphous material. The wear resistance of Cu based amorphous coating was found to be three times higher than that of pure Cu coating. The 3-point bending test results showed that the adhesion strength of Cu based amorphous coating layer was higher than that pure Cu coating. It was also observed that hard Cu base amorphous particle could easily deform soft substrate by particle collisions and thus generated strong adhesion between coating and substrate. However, the amorphous coating layer unexpectedly represented lower corrosion resistance than pure Cu coating, which might be resulted from the higher content of porosity in the cold sprayed amorphous coating.

• Journal of ILASS-Korea
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• v.27 no.3
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• pp.117-125
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• 2022

This study examines whether engine fuel efficiency is improved by optimization of the exhaust valve timing in a state where the intake valve timing has been optimized in a small turbo gasoline engine that has intake cams and exhaust cams with fixed valve opening periods. When the exhaust valve is opened late, the expansion stroke is longer, and the efficiency can be improved. A 2-cylinder turbo gasoline engine with 0.8 liters of displacement and an MPI (Multi Point Injection) fuel system was used. The engine was operated at 1,500 and 3,000 rpm, and the load conditions included a partial load of 50 N·m and a high load of 70 N·m. Data was recorded as the exhaust valve timing was controlled, and this was used to calculate the efficiency of combustion using a heat release, the fuel conversion efficiency, and the pumping loss. Results and the hydrocarbon concentrations in the exhaust gas were compared for each condition. Experiment results confirmed that additional fuel efficiency improvements are possible through exhaust valve timing control at 1,500 rpm and 50 N·m. However, in other operating conditions, fuel efficiency improvements could not be obtained through exhaust valve timing control because cases where the pumping loss and fuel/air mixture slip increased when the exhaust valve timing changed and the fuel efficiency declined.

• Journal of ILASS-Korea
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• v.29 no.2
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• pp.68-74
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• 2024

As awareness of environmental pollution problems increases worldwide, interest in air pollutants is increasing. In particular, NOx and PM, which are major pollutants in diesel vehicles, are contributing significantly to emissions. As a result, its importance is increasing. In this study, based on research results applied to large diesel vehicles, the problem of natural regeneration caused by low exhaust gas temperature during low speed and low load operation is solved by applying a complex regeneration DPF that is not affected by temperature conditions to small diesel vehicles. The feasibility of application to small diesel vehicles was reviewed by measuring the emission reduction efficiency. As a result of the engine test, the power reduction rate and fuel consumption rate before and after device installation under full load conditions were 2.9% decrease and 3.5% increase, respectively, satisfying the standard for a 5% reduction, and as a result of the regeneration equilibrium temperature (BPT) test, the regeneration temperature was 310℃. appeared at the level. The reduction efficiency test results for the actual vehicle durability test equipment showed 97.3% PM, 51.0% CO, and 31.1% HC, while the city commuter vehicle had PM 97.5%, CO 61.7%, HC 40.0%, and the school bus vehicle had PM 96.8%, CO 44.4%, HC 34.3%, and low-speed logistics vehicles showed a reduction efficiency of 98.2% for PM, 36.0% for CO, and 45.7% for HC. Based on the results of this study, in the future, it is necessary to secure DPF technology suitable for all vehicle types through actual vehicle application research on temperature condition-insensitive composite regenerative DPF for medium-sized vehicles.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.3
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• pp.275-283
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• 2013

An injector that uses methane gas ($CH_4$) and liquid oxygen ($LO_x$) as propellants was designed to verify the combustion characteristics of an engine that uses methane, which is one of the next-generation propellants. A swirl/shear coaxial-type injector was used, and flow analysis was performed using Fluent to determine the main design parameters of the injector. A hydraulic test was performed to understand the atomization and spray pattern characteristics of the injector. Next, a combustion test was performed at the design point to understand the ignition and combustion stability. Additional combustion tests were performed according to the O/F ratio to investigate the combustion characteristics and stabilities using the characteristic exhaust velocity ($C^*$) and fluctuation of the chamber pressure. The experimental results showed that the combustion efficiency was greater than 90%, and the pressure fluctuation was lower than 2% under all conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.4
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• pp.299-304
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• 2013

The HAN which is an ionic liquid is a non-toxic monopropellant with high storability, and its specific impulse can be increased by blending methanol, thereby it can substitute the hydrazine. The HAN was synthesized by acid-base reaction of hydroxylamine and nitric acid, and the blending ratio of HAN and methanol is 8.2:1. The iridium catalyst was used to decompose the HAN, and 1 N class thruster with shower head type injector having one orifice was used to evaluate the HAN/Methanol propellant. The thermal stability of distributor was increased by using ceramic material to endure the high temperature of product gas. The preheating temperature of catalyst should be $400^{\circ}C$ at least for the complete decomposition. The feeding pressure should be increased to increase the $C^*$ efficiency, thereby the decomposition performance was decreased upstream catalyst, and the performance of thruster was decreased. The fine metal mesh was inserted after the injector to improve the atomization of propellant, thereby it can settle the performance decrease problem. The phenomenon of performance decrease was remarkably improved owing to the insertion of fine metal mesh.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2001.11a
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• pp.30-30
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• 2001

$Bi_2Te_3$계 열전재료는 200~400K 정도의 저온에서 네어지 변환효율이 가장 높은 재료로써 열전냉각, 바런재로 등에 응요하기 위하여ㅠ 제조법 및 특서에 관한 많은 연구가 진행되어 왔다. $Bi_2Te_3$계 화합물은 rhombohedral의 결정 구조를 가지는 층상 화 ;물로 결정대칭성으로 인해 연전기적으로 큰 이방성을 나타낸다. 현재는 일반향용고법에 의해서 입자를 a축 방향으로 성장시켜 큰 결정립을 가진 다결정재료를 사용하고 있으나, c면이 매우 취약하기 때문에 가공서이 나쁘다. 따라서 이와같은 단점을 개선하기 위하여 기계적 강도를 높일 수 있는 가공공정 및 합금설계에 대한 연구가 활발히 진행되고 있다. 측히 열간 압출법으로 제조된 열전재료는 결정립의 미세화와 높은 이방성으로 성능지수와 기계적 강도를 향상시킬 수 있다는 연구결과가 보고되고 있다 또한 Schultz드의 연구결과에 의하면 $Bi_2Te_3$ 계 열전재료는 소성변형에 의하여 발생한 점결함에 의하여 캐리어 농도가 변화되며 이로 인하여 재료의 전기적 성질이 결정된다고 하였다. 따라서 상당히 큰 소성가공량과 열전측성과의 관계를 규명하는 것은 매우 중요하다. 이에 본 연구에서는 압출변수 중 소성가공량에 중요한 변수로 작요아는 압출비를 변화시켜 최적의 열간 소성가공량을 검토하고, 이에 따른 열전측성과 압출비와의 상관관계에 대하여 연구하는 것을 목적으로 하였다. 연구에 사용된 N형의 조성은$Bi_2Te_{2.75}Se_{0.15}$로서 순도 99.99를 사용하였고, dopant로 0.1wt%의 $SbI_3$를 사용하였다. $Bi_2Te_{2.75}Se_{0.15}$ 분말은 가스분사법(Gas atomization Process)를 이용하여, 용탕제조시 아르곤가스로 산화를 방지하였고, 냉매로는 질소가스를 이용하였다. 제조된 분말을 기ㅖ적 분급법을 이용하여 분급하였고, 냉매로는 질소가스를 이용하였다. 제조된 분말을 기계적 분급ㅂ법을 이용하여 분급하였고, 압출에 이용된 분말은 250$\mu\textrm{m}$이하의 크기를 사용하였다. 또한 분말제조과정 중 형성되는 표면산화층을 제거하기 위하여 36$0^{\circ}C$에서 4시간동안 수소 환원처리를 행하였다. 제조된 분말은 열간 압출을 위하여 Aㅣcan에 넣고 냉간성형체를 만들고, 진공처리를 한 후 밀봉하여 탈가스처리를 하였다. 압출다이는 압출비가 각각 28:1과 16:1인 평다이(9$0^{\circ}C$)를 사용하여 각각 내경이 9, 12cm이고, 길이가 50, 30cm인 압출재를 제조하였다. 열간압출한 후의 미세조직을 광학현미경으로 압출방향에 평행한 방향과 수직방향으로 관찰하였고, 열간 압출재 이방성을 검토하기 위하여 X선 회절분석을 실실하여 결정방위를 확인하였다. 전기 비저항 및 Seebeck 계수 측정을 위하여 각각 2$\times$2$\times$10$mm^3$ 그리고 5$\times$5$\times$10$mm^3$ 크기의 시편을 준비하였다.준비하였다.

• Journal of Powder Materials
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• v.25 no.2
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• pp.137-143
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• 2018

In this study, two types of SKD61 tool-steel samples are built by a selective laser melting (SLM) process using the different laser scan speeds. The characteristics of two kinds of SKD61 tool-steel powders used in the SLM process are evaluated. Commercial SKD61 tool-steel power has a flowability of 16.68 sec/50 g and its Hausner ratio is calculated to be 1.25 by apparent and tapped density. Also, the fabricated SKD61 tool steel powder fabricated by a gas atomization process has a flowability of 21.3 sec/50 g and its Hausner ratio is calculated to be 1.18. Therefore, we confirmed that the two powders used in this study have excellent flowability. Samples are fabricated to measure mechanical properties. The highest densities of the SKD61 tool-steel samples, fabricated under the same conditions, are $7.734g/cm^3$ (using commercial SKD61 powder) and $7.652g/cm^3$ (using fabricated SKD61 powder), measured with Archimedes method. Hardness is measured by Rockwell hardness testing equipment 5 times and the highest hardnesses of the samples are 54.56 HRC (commercial powder) and 52.62 HRC (fabricated powder). Also, the measured tensile strengths are approximately 1,721 MPa (commercial SKD61 powder) and 1,552 MPa (fabricated SKD61 powder), respectively.

• Journal of the Korean Chemical Society
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• v.50 no.1
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• pp.14-22
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• 2006

the basic model of chemical reactor using glow discharge, we used cathode discharge cell with vacant cavity in the middle. Currently glow discharge is widely studied as a radiation source or atomization device in atomic spectroscopy and remarkable technological achievements are made through the graft with other analysis devices such as microanalysis and steel analysis.1 Additionally, as the characteristics of basic glow discharge and radiation have been reviewed many times, those results could be used in this experiment.2-3 In 1993, an article regarding the treatment of poisonous gas in the air using low temperature plasma was published. According to this article, if DC Glow Discharge is used under continuous atmospheric flow, poisonous gases such as SO2 and NO can be removed.4 Based on those findings, we designed highly efficient reactor where stable air plasma is composed and all air flow pass the negative glow area passing through the tube. It was observed that the cathode tube type glow discharge developed in this study would be economical, easy to use and could be used as radiation source as well.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.1
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• pp.98-103
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• 2017

In this study, contributes to improving the state of this problem using cavitation by ultrasonic energy to reduce fuel costs, which take up a considerable part of ship operation costs, by making the use of on-board blended fuel oil more stable. An experiment simulating on-board blending methods was completed. Fuel (M.G.O & MF-180) was mixed at a volume ratio of 0.25:0.75 and, 0.75:0.25, and the effect of ultrasonic energy on blended fuel oil was examined after applying ultrasonic energy to blended fuel oil using an ultrasonic treatment unit. With the results, we confirmed the blending problem reported by vessels and residual carbon was reduced by up to 28.4%. In addition, based on the results for reduction of residual carbon content and dispersion stability, it was confirmed that the collapse pressure of the cavity due to the ultrasonic energy was effective to atomization of fuel particle and the temporary availability of mixed fuel containing a heavy fuel increased.