• 한국자동차공학회논문집
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• 제12권2호
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• pp.9-16
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• 2004

Close-coupled catalyst (CCC) can reduce the engine cold-start emissions by utilizing the energy in the exhaust gas. However, in case the engine is operated at high engine speed and load condition, the catalytic converter may be damaged and eventually deactivated by thermal aging. Excess fuel is sometimes supplied intentionally to lower the exhaust gas temperature avoiding the thermal aging. This sacrifices the fuel economy and exhaust emissions. This paper describes the results of an exhaust heat exchanger to lower the exhaust gas temperature mainly under high load conditions. The heat exchanger was installed between the exhaust manifold and the inlet of close-coupled catalytic converter. The exhaust heat exchanger successfully decreased the exhaust gas temperature, which eliminated the requirement of fuel enrichment under high load conditions. However, the cooling of the exhaust gas through the heat exchanger may cause the deterioration of exhaust emissions at cold start due to the increment of catalyst light-off time.

• 한국분말재료학회지
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• 제19권2호
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• pp.110-116
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• 2012

This study investigated the effects of annealing environment for the densification and purification properties of pure titanium coating layer manufactured by cold spraying. The annealing was conducted at $600^{\circ}C$/1 h and three kinds of environments of vacuum, Ar gas, and $5%H_2+Ar$ mixture gas were controlled. Cold sprayed Ti coating layer (as sprayed) represented 6.7% of porosity and 228 HV of hardness, showing elongated particle shapes (severe plastic deformation) perpendicular to injection direction. Regardless of gas environments, all thermally heat treated coating layers consisted of pure ${\alpha}$-Ti and minimal oxide. Vacuum environment during heat treatment represented superior densification properties (3.8% porosity, 156.7 HV) to those of Ar gas (5.3%, 144.5 HV) and $5%H_2+Ar$ mixture gas (5.5%, 153.1 HV). From the results of phase analysis (XRD, EPMA, SEM, EDS), it was found that the vacuum environment during heat treatment could be effective for reducing oxide contents (purification) in the Ti coating layer. The characteristic of microstructural evolution with heat treatment was found to be different at three different gas environments. The controlling method for improving densification and purification in the cold sprayed Ti coating material was also discussed.

• PNF and Movement
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• 제7권3호
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• pp.29-38
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• 2009

Purpose : The aim of this study is to examine the effect of the phenol compound-cold therapy plus exercise therapy on the carrageenan(CAR)-induced muscle pain. Method : Mice were injected 0.1ml of 2% CAR into the gastrocmemius(GAS) muscle for the induction of muscle pain. After 4 hours from the injection of CAR, the cold therapy with 1% syringic acid was done to GAS muscle. After 2 hours from cold therapy, the exercise therapy such as muscle stretching, climing- and declining-movements was performed three times interval of 10 minutes in each experimental group. After 4, 10 and 24 hours from CAR-induced muscle pain, the measurements of muscle diameter, paw withdrawal latency(PWL) and, tail flick latency(TFL) were carried out. Results : In this study, the thickness of GAS muscle in CAR-induced muscle pain significantly increased compared with control. While, the thickness of GAS muscle adopted cold syringic acid-therapy with exercise-therapy group was significantly decreased than that of CAR-induced muscle pain. In the measurements of PWL and TFL, cold syringic acid-therapy with exercise-therapy group was remarkably increased than CAR-induced muscle pain group in PWL and TFL. All measurements were showed significantly different between the treated-group and the treated-time. Conclusions : From these results, it is suggested that the cold syringic acid-therapy with exercise-therapy such as muscle stretching, climing- and declining-movement was effective in the prevention of CAR-induced muscle pain by the decrease of muscle thickness and the increase of PWL and TFL.

• 한국수소및신에너지학회논문집
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• 제35권3호
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• pp.318-323
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• 2024

In this paper, computer modeling works have been performed for the power generation Rankine cycle using new working fluids and liquefied natural gas (LNG) cold heat. PRO/II with PROVISION released January 2023 from AVEVA company was used, and Peng-Robinson equation of the state model with Twu's alpha function was selected for the modeling of the power generation cycle. Optimal working fluid composition was determined to maximize LNG cold heat to increase power generation efficiency and net power production.

• 한국자동차공학회논문집
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• 제16권3호
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• pp.94-101
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• 2008

Since regulations of exhaust emissions are continuously reinforced, studies to reduce harmful emissions during the cold start period of SI engines have been carried out very extensively worldwide. During the cold start period, raising the temperature of cold exhaust gas is a key strategy to minimize the light-off time of three way catalysts. In this study, a synthetic gas containing a large amount of hydrogen was injected into the exhaust manifold to raise the exhaust gas temperature and to reduce harmful emissions. The authors tried to evaluate changes in exhaust gas temperature and harmful emissions through controlling the engine operating parameters such as ignition timings and lambda values. Also the authors investigated both combustion stability and reduction of harmful emissions. Experimental results showed that combustion of the synthetic gas in the exhaust manifold is a very effective way for solving the problems of harmful emissions and light-off time. The results also showed that the strategy of retarded ignition timings and increased air/fuel ratios with ESGI is effective in raising exhaust gas temperature and reducing harmful emissions. Futhermore, the results showed that engine operating parameters ought to be controlled to lambda = 1.2 and ignition timing = $0{\sim}3^{\circ}$ conditions to reduce harmful emissions effectively under stable combustion conditions.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.90-90
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• 2017

Cold spray (Cold gas dynamic spray, kinetic spray) is the latest spray coating process that is known as solid state deposition process. In cold spray, inert gases (typically nitrogen and helium) accelerate powder particles prior to impact onto the substrate. Accelerating particles start to deposit onto the substrate after reaching certain critical velocities depending on the coating materials and substrate. Since process gas temperatures are kept below to melting temperature of the coating materials, it is possible to spray temperature sensitive materials such as copper and titanium, nanocrystal materials, and amorphous metals without affecting the phase change and oxide formation. It is also possible to deposit thick coatings because cold spray coatings present compressive residual stresses. This ability to deposit thick coatings is suitable to repair or rebuild parts as an additive manufacturing process. In this presentation, cold spray is introduced and compared to other additive manufacturing processes such as laser and electron beam based processes. It is also presented some applications especially in the view point of additive manufacturing process.

• 한국자동차공학회논문집
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• 제9권2호
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• pp.67-74
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• 2001

A synchronized secondaty air injection method has been developed to hydrocarbon emission by injecting secondary air intermittently into exhaust port. The method has been tested in a single cylinder spark-ignition engine operating at cold-steady / cold-start conditions. Effects of air injection timing, intake pressure and engine air-fuel ratio have been investigated at cold-steady condition. Also, hydrocarbon emission and exhaust gas temperature with catalytic conberter are compared with a continuous SAI method and base condition at cold-start condition. Resules show that hydrocarbon reduction rate and exhaust gas temperature are sensitive to the timing of synchronized SAI. At cold-steady condition, HC emission is minimum at engine air-fuel ratio of 10. At cold-start condition, the accumulated hydrocarbon emission during the first 120 s decreases about 56% and 22% with the synchronized and continuous SAI, respectively, compared to that of base condition.

• 열처리공학회지
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• 제27권1호
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• pp.15-22
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• 2014

This study is to investigate the phase changes and cold workability after isothermal transformation at $780^{\circ}C$ by using the high temperature gas nitrided (HTGN) STS 430 ferritic stainless steel specimens. The phase diagram of STS 430 steel obtained by calculation showed that the phase appeared at $1100^{\circ}C$ showed as ${\alpha}+{\gamma}{\rightarrow}{\gamma}{\rightarrow}{\gamma}+Cr_2N{\rightarrow}{\gamma}+Cr_2N+CrN$ with increasing nitrogen concentration. Also, the transformation of ${\gamma}{\rightarrow}Cr_2N$ during heat treatment isothermally at $780^{\circ}C$, nitrogen pearlite with lamellar type was fully formed at the nitrogen permated surface layer for 10 hrs. However, this transformation was not completed for 1 hr, resulting nitrogen pearlite plus martensite. The cold rolled specimen of isothermally transformed at $780^{\circ}C$ for 10 hrs after high temperature gas nitriding decreased the layer thickness of nitrogen pearlite inducing the deformation of hard $Cr_2N$ phase. the dissolution rate of $Cr_2N$ phase increased rapidly with increasing cold rolling ratio. Specimens with the microstructure of nitrogen pearlite (isothermally transformed at $780^{\circ}C$ for 10 hrs) were possible to cold rolling without crack formation. However, the mixed structures of nitrogen pearlite + martensite (isothermally transformed at $780^{\circ}C$ for 1 hr) were impossible to cold deformation without cracking.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권6호
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• pp.387-394
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• 2000

This paper presents a method of cold gas flow-field analysis within puffer type GCB(Gas Circuit Breaker). Using this method, the entire interruption process including opening operation of GCB can be simulated successfully. In particular, the distortion problem of the grid due to the movement of moving parts can be dealt with by the fixed grid technique. The gas parameters such as temperature, pressure, density, velocity through the entire interruption process can be calculated and visualized. It was confirmed that the time variation of pressure which was calculated from the application of the method to a model GCB agreed with the experimental one. Therefore it is possible to evaluate the small current interruption capability analytically and to design the interrupter which has excellent interruption capability using the proposed method. It is expected that the proposed method can reduce the time and cost for development of GCB very much. It also will be possible to develop the hot-gas flow-field analysis program by combining the cold-gas flow field program with the arc model and to evaluate the large current interruption capability.

• 한국가스학회지
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• 제14권1호
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• pp.42-46
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• 2010

LNG (Liquefied Natural Gas)기지의 LNG 저장탱크에서 BOG (Boil Off Gas)가 약 0.5 vol%/day로 자연적으로 생성된다. 이를 회수하기 위해서 기존에는 LNG와 BOG를 1:12의 질량비로 직접 접촉시켜 액화시켰다. 이 공정은 단순하지만 하절기에는 LNG 사용량 저하로 인해 공정운영의 어려움이 있다. 이러한 단점을 보완하기 위해 대안된 LNG 냉열을 사용하는 간접접촉방식을 HYSYS를 이용하여 분석해보고 직접접촉방식과 BOG 재액화 효율비교를 통해 분석하여 유리한 공정을 도출하였다.