• 한국자동차공학회논문집
• /
• 제22권4호
• /
• pp.121-130
• /
• 2014

This paper is the second investigation on the effects of intake flow control methods on the part load performance in a spark ignition engine. In the previous work, two control methods, port throttling and masking, were compared with respect to lean misfire limit, fuel consumption and emissions. In this work, the effects of these two methods on EGR characteristics were studied and simultaneously the differences between EGR and lean combustion as a dilution method were investigated. The results show that EGR limit is expanded up to 23% and 3 ~ 5% improvement in the fuel consumption are achieved around 8 ~ 13% rates by the flow controls comparing with 10% limit and 1.5% reduction around 3% rate of non-control case. The masking method is more effective on the limit expansion than throttling as like as lean misfire limit; however there is no substantial difference in fuel consumptions improvement regardless the control methods except high load condition. Also it is observed that there exist critical EGR rates around which the combustion performance and NOx formation change remarkably and these rates generally coincide with optimum rates for the fuel consumption. In addition, dilution with fresh air is much more advantageous than that of the exhaust gas from the view point of dilution limit and fuel consumption, while utilization of the exhaust gas is more effective on NOx reduction in spite of considerably small dilution compared with the use of fresh air. Finally, the improvement of fuel consumption by massive EGR is highly dependent on the EGR limit at which the engine runs stably, therefore the stratified combustion technique might be a best solution for this purpose.

• Journal of Ship and Ocean Technology
• /
• 제3권4호
• /
• pp.15-22
• /
• 1999

It is known that lubrication effect of an air cavity can reduced a drag of a ship. The present study intends to utilize the phenomena for the drag reduction of a passenger ship now operating in a lake. A scaled model of the model when air cavities are formed under the bottom of the model. Model experiments have been performed to determine adequate air supply rates, proper shapes and locations of air supply nozzles. It is shown that energy saving of mere than 10% can be achieved at the design speed of the ship even after excluding additional power consumed for air supplying. Multiple air supply nozzles, if allocated properly, are more effective than single one in resistance reduction of the ship.

• 대한화학회지
• /
• 제30권5호
• /
• pp.409-414
• /
• 1986

황산용액에서 에탄올에 의한 $VO_2^+$이온을 환원시키면 황산바나딜(IV)가 생성된다. 생성물 VOS$O_4$를 포함하는 용액에 대한 분광학적 결과가 보고된다. 에탄올에 의한 $VO_2^+$의 환원에 대한 속도론적 연구는 35${\circ}C$와 50${\circ}C$에서 행하여 졌다. $VO_2^+$의 환원반응메카니즘이 논의되었다.

• 한국환경보건학회지
• /
• 제25권3호
• /
• pp.1-6
• /
• 1999

This study was conducted to survey trihalomethane(THMs) levels in finished water of J water treatment plant and examine its reduction by powder activated carbon(PAC) treatment. Samples were collected weekly based and head-space technique was employed to determine THMs levels by G.C-ECD. THMs levels in finished waters were highest in August and showed close relationship with water temperature. All the samples satisfied the drinking water limit(100 ${\mu}$g/l) for THMs. The individual formation rates of THMs were 64.8% for CHCl$_3$, 28.4% for CHCl$_2$BR, 6.5% for CHClBr$_2$ and 0.3% for CHBr$_3$, respectively and showed little monthly difference. The reduction efficiency of THMs formation by PAC treatment was 67% during July and August. Bromine substituents were more efficiently reduced than CHCl$_3$ by PAC.

• 전자공학회논문지B
• /
• 제33B권3호
• /
• pp.126-132
• /
• 1996

In this paper, the complexity reduction method for QCELP speech coder (IS-96) without any perfomrance degradation is proposed for the vecoder of CDMA digital cellular system. The energy terms in pitch parameter search and codebook search routines that require large computations are calculated recursively by utilizing the overlapped structure of code vectors in adaptive codebook and excitation codebook. The additional complexity reduction in the codebook search routine can be achieved by using a simple form in calculation of the energy term when the initial codebook value is zero. In the case of lower transmission rates such as 4,2,1 kbps, the complexity reduction by recursive calulations of energy term is increased.

• 한국입자에어로졸학회지
• /
• 제9권4호
• /
• pp.271-277
• /
• 2013

This article reports the drag reduction phenomenon of aqueous suspensions containing carbon nanotubes (CNTs) flowing through horizontal tubes. Stable nanofluids were prepared by using a surfactant. It is found that the drag forces of CNT nanofluids were reduced at specific flow conditions compared to the base fluid. It is found that the friction factor of CNT nanofluids was reduced up to approximately 30 % by using CNT nanofluids. Increased kinematic viscosities of CNT nanofluids are suggested to the key factors that cause the drag reduction phenomenon. In addition, transition from laminar to turbulent flow is observed to be delayed when CNT nanofluids flow in a horizontal tube, meaning that drag reduction occurs at higher flow rates, that is, at higher Reynolds numbers.

• 한국생산제조학회지
• /
• 제22권3호
• /
• pp.421-428
• /
• 2013

The current vibration reduction methods for positioning systems lead to either complicated motion or the need for additional hardware when the positioning systems carry out frequent short-distance movements. This paper proposes a simple yet efficient vibration reduction method for positioning systems subjected to frequent short-distance movements. The essence of the proposed method is the trapezoidal or triangular velocity profiles, whose acceleration/deceleration rates are designed to be related to the natural frequency of concern. The combined use of the proposed method and the input shaping method is also proposed for the possible application to multi-mode systems. Experiments are performed to validate the proposed method. The simulation and experiments prove that the proposed method is of great use for residual vibration reduction in positioning systems subjected to frequent short-distance movement.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 1998년도 유체기계 연구개발 발표회 논문집
• /
• pp.240-247
• /
• 1998

Leakage vortices formed near blade tip causes an increase of total pressure loss near casing endwall region and as a result, the efficiency of rotor decreases. The reduction of rotor efficiency is related to the size of tip clearance. In this study, the three-dimensional flowfields in an axial flow rotor were calculated with varying tip clearance under various flow rates, and the numerical results were compared with experimental ones. The effects of tip clearance and attack angle on the leakage vortex and overall performance, and the less distributions were investigated through numerical calculations. In this study, tip leakage flow rate and total pressure loss by tip clearance were evaluated using numerical results and aprroximate equations were presented to evaluate the reduction of rotor efficiency by tip leakage flow.

• 전기학회논문지
• /
• 제57권11호
• /
• pp.2027-2034
• /
• 2008

There are concerns on possible health effects from exposure to electromagnetic fields. One reflection of this concerns is the considerable controversy, delay, and cost increases involved in the construction of power lines and facilities. To cope with such challenges, in this paper we investigated magnetic fields reduction techniques such as general compaction, in' span compaction, cruciform, vertical, 3 way splits phase, and 4way splits phase. As results, we found general compaction and 4 way splits phase could reduce magnetic fields up to 90%, while cruciform, vertical, and 3 way splits phase gave lower reduction rates of 30% because these configurations were similar to a current type of low reactance arrangement. We also knew 1 spacer in span compaction was appropriate in Korea in view of effectiveness and economy.

• Parasites, Hosts and Diseases
• /
• 제44권3호
• /
• pp.255-257
• /
• 2006

A field trial on the control effect of fipronil poison bait against German cockroaches (Blatella germanica) was carried out at different restaurant types in Sinchon, Seoul, Republic of Korea. Monitoring was performed applying food baited traps for 2 days per week. Reduction rates of German cockroaches by applying fipronil baits were 90.9% at Korean restaurants, 96.4% at Chinese restaurants, and 89.4% in beer hall kitchens after 4 weeks of the treatment. Overall average of the reduction rate was 93.9%. As the natural reduction rate at untreated restaurants was 11.5% after 4 weeks, a correction of the average reduction rate by applying the Abbot formula was 93.1 %.