• 대한기계학회논문집B
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• 제20권10호
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• pp.3262-3271
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• 1996

Flow patterns were measured in a shrouded centrifugal impeller. The flow rate in measurements was fixed at the value corresponding to a nearly zero incidence at the blade inlet. By using a single slanted hot-wire probe and a Kiel probe mounted on the impeller hub disk, the 3-D relative velocities and the rotary stagnation pressures were measured in seven circumferential planes from the inlet to the outlet of impeller rotating at 700 rpm, and the static pressure distribution along flow passage and the slip factor at impeller outlet were calculated from the measured values. From these measured data, the primary and secondary flows, the wake production and the static pressure rise in the impeller passage were investigated. Furthermore, the secondary flow patterns and the wake's location in this impeller passage were compared with those of the unshrouded impeller.

• 한국소음진동공학회논문집
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• 제25권8호
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• pp.532-538
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• 2015

In a reciprocating compressor, highly impulsive pressure fluctuations induced by a reciprocating piston give rise to serious noise and vibration problems. A muffler is frequently used to reduce this impulsive noise, but also has adverse effects on compressor performance due to additional pressure drop and heat transfer of refrigerants through it. Therefore, the flow and acoustic performances of mufflers used in a compressor should be considered simultaneously. In this study, both of flow and acoustic performances of mufflers are investigated using computational fluid dynamic techniques by solving full three-dimensional compressible Reynolds-Averaged Navier-Stokes equations. For validation purpose, the numerical method is initially applied to predict the transmission loss of a simple expansion muffler, and its predicted results show good agreements with theoretical and experimental results. Then, the flow and acoustic performances of an existing muffler is numerically investigated. On the basis of the analysis results, a new muffler is purposed and its performances are compared with the existing one. Improved performances of the new muffler are confirmed.

• International Journal of Automotive Technology
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• 제7권6호
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• pp.645-652
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• 2006

This paper is concerned with an experimental study of a turbocharged diesel engine operating on dimethyl ether(DME). The combustion and emission characteristics of DME engine were investigated. The results showed that the maximum torque and power with DME could achieve a greater level compared to diesel operation, particularly at low speeds; the brake specific fuel consumption with DME was lower than the diesel at low and middle engine speeds. The injection delay of DME was longer than that of diesel. However, the maximum cylinder pressure, maximum pressure rise rate and combustion noises of DME engine were lower than those of diesel. The combustion velocity of DME was faster than that of diesel, resulting in a shorter combustion duration of DME. Compared with the diesel engine, $NO_x$ emissions of the DME engine were reduced by 41.6% on ESC data. The DME engine was smoke free at all operating points of the engine.

• 대한기계학회논문집B
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• 제38권6호
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• pp.451-464
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• 2014

본 연구에서는 HCCI엔진의 과급조건에서 EGR의 영향에 대하여 수치해석적인 방법으로 연구하였다. 수치해석은 CHEMKIN-PRO에 있는 single-zone model을 사용하였고 연료로는 N-heptnae, Iso-octane 그리고 PRF50을 사용하였다. 사용된 연료의 화학반응 매커니즘과 열역학적 변수들은 Lawrence Livermore National Laboratory(LLNL)의 모델을 사용하였다. 연소상의 변화는 열효율에 큰 영향을 미치게 되므로 이영향을 배제하기 위해 본 연구에서는 CA50을 $365^{\circ}CA$($5^{\circ}CA$ aTDC)로 일정하게 고정하였다. 연구결과 EGR의 영향으로 줄어든 산소의 영향에 의해 저온산화반응과 NTC, 고온산화반응이 모두 약화되고 열발생률이 감소하는 것을 확인할 수 있었다. 과급과 EGR을 함께 사용하게 되면 과급에 의해 증가한 산소량과 연료의 영향으로 인해 연소가 강화되어 저온산화반응, NTC, 고온산화반응이 강화되고 열 발생률이 증가하는 것을 확인할 수 있었다. EGR만을 사용하는 경우 IMEP가 감소하는 경향을 나타내지만 과급과 EGR을 함께 사용하는 경우 과급의 영향으로 인해 IMEP가 크게 증가하여 낮은 압력상승률과 높은 출력을 함께 얻을 수 있는 것을 확인하였다.

• 한국분무공학회지
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• 제16권1호
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• pp.51-57
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• 2011

An experimental study was performed to explore characteristics of combustion and exhaust emissions in the compression ignition engine of RCCI (reactivity controlled compression ignition) using diesel-gasoline dual fuel. A dual-fuel reactivity controlled compression ignition concepts is demonstrated as a promising method to achieve high thermal efficiency and low emissions. For investigating combustion characteristics, engine experiments were performed in a light-duty diesel engine over a range of SOIs (start of injection) and gasoline percents. The experimental results showed that cases of diesel-gasoline dual fuel combustion is capable of operating over a middle range of engine loads with lower levels of NOx and soot, acceptable pressure rise rate, low ISFC (indicated specific fuel consumption), and high indicated thermal efficiency.

• 한국산업융합학회 논문집
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• 제19권1호
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• pp.31-38
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• 2016

Since the oil shock of 1970's there was a strong upward tendency for the use of the high viscosity and poorer quality fuels. Therefore the misfiring engine occurs due to the decrease of quantity injected for lean burn and emission control in Compression Ignition Common Rail Direct Injection diesel engine. In this study, it is designed and used the test bed which is installed with fuel injector controller. In addition to equipped engine using CRDI by controlling the injection timing with mapping modulator, it has tested and analyzed the engine performance and combustion characteristics, as it is varied that they are the operating parameters: fuel injected quantity, engine speed and injection timing.

• Interaction and multiscale mechanics
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• 제4권2호
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• pp.139-153
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• 2011

In this paper we develop a fully anisotropic pressure and temperature dependent model to investigate the effect of the microstructure on the shock response of ${\beta}$-HMX molecular single and polycrystals. This micromechanics-based model can account for crystal orientation as well as crystallographic twinning and slip during deformation and has been calibrated using existing gas gun data. We observe that due to the high degree of anisotropy of these polycrystals, certain orientations are more favorable for plastic deformation - and therefore defect and dislocation generation - than others. Loading along these directions results in highly localized deformation and temperature fields. This observation confirms that most of the temperature rise during high rates of loading is due to plastic deformation or dislocation pile up at microscale and not due to volumetric changes.

• 한국유체기계학회 논문집
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• 제9권3호
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• pp.44-48
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• 2006

Comprehensive experimental works are carried out for the optimal design of a centrifugal blower adopted in an indoor unit of an air-conditioner. The models for consideration are typical multi-blade turbo blower and limit loaded one, respectively. The main interest lies on the fluid dynamics performance when the blower Is installed in the practical system. The methodologies are an experimental estimations with a wind tunnel for blower performance and PIV measurement for the detail flow information. A centrifugal blower with limit loaded fan shows pronounced performances in terms of the flow rate and static pressure rise and the reason is explained by the precise measurement of the flows between blades using PIV. Consequently, it is found that the blower is proper for the flows with a resistance in down stream such as a heat exchanger.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.181-186
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• 2010

A numerical study was conducted to predict the performance curve of a canned motor pump for SMART(System Integrated Modular Advanced ReacTor). The study used a computational domain which included not only the pump but also a suction pipe and a volute casing with a discharging pipe in order to simulate an experimental setup. The ANSYS CFX program was utilized to obtain flow characteristics inside the pump as well as the overall pressure rise across the pump operating on- and off-design points. Computed results showed that the performance of the pump at off-design points was much lower than expected. Special attention was made to find the cause of the low performance of the pump operating at low flow rate.

• 한국산업융합학회 논문집
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• 제6권4호
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• pp.307-313
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• 2003

A technique for the design of cooling tower fans with sweep is presented. This technique is developed using the equations for the one dimensional inviscid flow through the fan blade, the empirical equations, and the experimental correlations. A parabolic function is used to generate a sweep of the fan. Design data for the fan and the balde can be obtained for a given flow rate and a pressure rise. Also, the present method is used to construct the three dimensional model for the designed fan. Design data and the model show general characteristics of the axial propeller fan.