• Smart Structures and Systems
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• 제18권5호
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• pp.865-884
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• 2016

We have previously demonstrated a microfluidic elastomer, which changes apparent color and could have potential applications in smart windows. The practical use of such functional microfluidic systems requires rapid and uniform fluid displacement throughout the channel network with minimal amount of liquid supply. The goal of this simulation study is to design various microfluidic networks for similar applications including, but not limited to, the color-switching windows and compare the liquid displacement speed and efficiency of the designs. We numerically simulate and analyze the liquid displacement in the microfluidic networks with serpentine, parallel and lattice channel configurations, as well as their modified versions with wide or tapered distributor and collector channels. The data are analyzed on the basis of numerical criteria defined to evaluate the performance of the corresponding functional systems. We found that the lattice channel network geometry with the tapered distributors and collectors provides most rapid and uniform fluid displacement with minimum liquid waste. The simulation results could give an important guideline for efficient liquid supply/displacement in emerging functional systems with embedded microfluidic networks.

• 한국분무공학회지
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• 제10권4호
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• pp.8-15
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• 2005

The use of clean gaseous fuels for the purpose of high efficiency and low emission in automotive engines has tendency to increase in order to meet the reinforcing emission regulations and to efficiently utilize limited natural resources. Automotive companies developed and commercialized a LPG liquid injection system, which is mounted on LPLi(Liquid Phase LPG Injection) engines and vehicles based on this research trend. This research examines the biggest problem in LPLi engine, that is, the leakage characteristics of low viscosity LPG fuel according to the injector design variables. This study is also aimed to improve the performance of fuel-leakage in LPLi engine through the addition of a lubrication improver in HFRR(High Frequency Reciprocating Rig) facility. The needle displacement and the spring displacement of an LPLi injector are found to be already optimized. The possibility of a maximum of 70% leakage reduction compared to a conventional case, is verified when 1000ppm of a lubrication improvement material is added and 40% increase of a injector spring constant (K) is applied.

• Smart Structures and Systems
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• 제21권1호
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• pp.37-51
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• 2018

Tuned Liquid Dampers (TLDs) have gained wide acceptance as a system for structural control and energy dissipation. However, they face limitation caused by low damping in deep water, which affects their efficiency. Another problem with deep water TLDs is that not all water depth participates in energy dissipation. This paper investigated the effect of upper mounted baffles on the effectiveness of TLDs. The Vertical Blockage Ratio (VBR) of baffles ranged from 10% - 90%. The TLD (with and without baffle), structure, and combined structure with TLD (with and without baffles) were subjected to free and harmonic forced vibrations. Results indicated that baffles could significantly enhance the energy dissipation of TLDs, thus reducing structural responses more than structures equipped with ordinary TLDs. It was found that, there was an optimum value of VBR in which the TLD's efficiency was maximized. When TLD had an appropriate VBR, the structural acceleration and displacement responses were suppressed significantly up to 51% and 56%, respectively.

• 한국분무공학회지
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• 제25권1호
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• pp.34-39
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• 2020

Automotive manufacturers are applying technologies for greenhouse gas reduction such as vehicle weight reduction, engine downsizing, direct injection technology, variable valves and transmission performance improvement to achieve the targets for enhanced greenhouse gas and fuel consumption efficiency. In this paper, compared and analyzed greenhouse emissions according to engine capacity, engine displacement, curb weight and sales volume of hybrid and internal combustion engine passenger vehicles. Hybrid emit 32~39% less greenhouse gas than internal combustion engines through the combined mode test method. Hybrid electric vehicle's curb weight was about 7% heavier on average for the same engine displacement, while greenhouse gas was about 36% lower. It was confirmed that in order to reduce the emission of pollutants of greenhouse gases as well as the air pollutants, it is necessary to expand the supply of eco-friendly vehicles.

• 한국분무공학회지
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• 제27권3호
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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.

• Earthquakes and Structures
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• 제14권6호
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• pp.567-576
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• 2018

This manuscript introduces a new damping device which is composed of a water tank and a pendulum. The new damping device can be tuned to multiple frequencies. In addition, it has a higher energy dissipation capacity when compared with the conventional Tuned Liquid Dampers (TLDs). In order to evaluate the efficiency of this new damping device a series of free vibration and forced vibration tests were conducted on a scaled down single-story one-bay steel frame. Two different configurations were studied for the mass of the pendulum that included a completely and a partially submerged mass. It was observed that the completely submerged configuration led to 44% higher damping ratio when compared with the conventional TLD. In addition, the completely submerged configuration reduced the peak displacement response of the structure 1.6 times more than the conventional TLD. The peak acceleration response of the structure equipped with the new damping device was reduced twice more than the conventional TLD. It was also found that, when the excitation frequency is lower than the resonance frequency, the conventional TLD performs better than the partially submerged configuration of the new damping device.

• 한국분무공학회지
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• 제29권2호
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• pp.53-59
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• 2024

Cars are one of the main causes of air pollution in large cities, and 34.6% of domestic air pollution emissions come from mobile sources, of which cars account for 69.6%. In particular, the importance of nitrogen oxides (NOx) and particulate matter (PM), which are major pollutants in diesel vehicles, is increasing due to their high contribution to emissions. Therefore, in this study, the problem of natural regeneration caused by low exhaust gas temperature during low speed and low load operation was solved by applying a complex regeneration DPF that is not affected by temperature conditions to large diesel vehicles with higher driving time and engine displacement than small and medium-sized vehicles. And the feasibility of application to large diesel vehicles was reviewed by measuring the emission reduction efficiency. As a result of the reduction efficiency test on the actual vehicle durability product, PM showed a reduction efficiency of 84% to 86%, and the reduction efficiency of gaseous substances showed a high reduction efficiency of over 90%. The actual vehicle applicability test was completed with three driving patterns: village bus vehicle, police car, and road-going construction equipment vehicle, and no device problems occurred until the end of the test. Both load and no-load smoke measurement results showed a smoke reduction efficiency of over 96%.

• 한국수소및신에너지학회논문집
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• 제13권4호
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• pp.297-303
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• 2002

The purpose of study is obtaining low-emission and high-efficiency in LPi engine with hydrogen enrichment. The test engine was named variable compression ratio single cylinder engine (VACRE). The fuel supply system provides LPG/hydrogen mixtures based on same heating value. A varied sensors such as crank shaft position sensor (CPS) and hall sensor supplies spark timing data to ignition controller. Displacement of VACRE is $1858.2cm^3$. VACRE was runned 1400rpm with compression ratio 8. Spark timing was set MBT without knocking. Relative air-fuel ratio($\lambda$) of this work was varied between 0,8 and 1.5.

• 대한화학회지
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• 제32권6호
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• pp.593-602
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• 1988

크라운 에테르를 반복 사용 기능의 상이동 촉매(phase transfer catalyst ; PTC)로 유도하기 위해 고분자 물질로 지지된 크라운 에테르(polymer-supported crown ether ; Ps-CE)류를 합성하고, 이들 Ps-CE(solid phase)를 이용하여 액-고-액 3상 불균일계에서의 1-bromooctane(유기층)의 iodide(수용층) 친핵 치환 반응속도를 측정하고 그 상이동 촉매능을 연구검토하였다. Ps-CE류는 hydroxymethyl기를 지니는 크라운 에테르류를 합성한 후 이를 1∼2% cross-linked chloromethylated polystyrene 에그라프트시켜 제조하였다. 3상 불균일계치환반응은 반응기질의 농도에 의존하는 유사 일차반응이었고 반응속도상수$(k_{obsd})$는 사용한 촉매량에 비례하였으며, 가교밀도, 온도, 용매 등에 영향을 받음을 알 수 있었다. Ps-CE의 촉매능을 구조적으로 유사한 가용성 크라운 에테르의 촉매능과 비교하였으며, 반응 후 단순히 여과분리하고 이를 PTC로서 반복사용하였을때 촉매능의 감소없이 재사용이 가능함을 알 수 있었다. 반응의 활성화 엔탈피 및 엔트로피는 각각 10∼20kcal $mol^{-1}, 20~55eu.이었고 활성화 자유 에너지는 ∼30kcal mol^{-1}$,/TEX>이었다.

• 비파괴검사학회지
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• 제28권2호
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• pp.211-216
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• 2008

이 연구에서 다층구조물에서 각 모드에 대한 위상속도, 군속도, 감쇠 그리고 파형구조를 구하는 프로그램을 개발하였다. 판의 수와 재료 물성치를 변화시키면서 각 모드의 파형구조를 얻었다. 유체가 닿아 있는 구조물에서 유도파를 이용한 비파괴 검사의 성공여부는 에너지 손실을 최소화하는 모드선정의 최적화이다. 이 연구에서는 자유표면판재의 표면에서 정규화된 두께방향의 변위가 감쇠의 변화를 예측하기 위해서 사용되었으며 감쇠와 파형구조의 관계를 밝혔다. 이것은 유도파의 감쇠를 물이 닿아 있는 경우 복소수근을 찾는 수학적 어려움을 경감하면서 자유표면에서 두께방향 변위의 변화로부터 손쉽게 얻을 수 있다. 이 연구를 통하여 다층구조물에서 보다 민감하고 효율적인 비파괴 검사를 위한 유도파의 모드선정의 최적화 개념을 완성했다.