• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.5
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• pp.114-122
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• 1997

Nowadays, gasoline direct injection engines are being commercialized by virtue of improvement in control technology of spray, flow, air fuel ratio. The stratified charge type has the advantage of improving lean limit. The homogeneous type has the advantage of reducing engine-out hydrocabon emissions in the first 30 seconds after a cold start, in addition, improving transient air fuel ratio control. The vaporization and mixing if injected fuel with air has to e completed in a short time and the fuel film in cylinder and on piston has to be minimized. So, the flow and injection should be well controlled. This paper surveyed the spray characteristics of gasoline direct injection by using laser equipment and the combustion characteristics of the single cylinder engine using homogeneousas-mixture type gasoline direct injection.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1709-1712
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• 2003

Almost the on-off type solenoid valve is used to hydraulic system. It has a strong point that concerned about rapid response, electric and hydraulic characteristic at the same time. In this paper we produced the new type spool using the MR fluid different from the others. Also we controlled a cylinder position through PWM method. And using the AMESim software, We compared our new type spool valve with existed one from data of simulation and experiment.

• Journal of Power System Engineering
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• v.6 no.2
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• pp.82-87
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• 2002

For the dynamic behavior evaluation of a semi-active vibration control system, it is very important to use an accurate mathematical model for the hydraulic damper applied to the control system. In this study, a mathematical model for a symmetric type hydraulic damper was suggested. In this model, the effects of gas volume and oil temperature variation on the bulk modulus of oil were considered. The dynamic behavior of the damper was investigated by experiments and simulations. It was confirmed that the pressure variation, damping force, and mean pressure variation could be estimated with comparatively good precision by the suggested mathematical model. Moreover, it was shown that excessive pressure rise can be generated by the oil expansion due to the heat energy transformed from the exciting energy of the damper for a short period of the damper operation.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.11a
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• pp.129-135
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• 1999

A numerical analysis between the piston and cylinder in swash plate type hydraulic piston pumps under reciprocating motion is presented. A finite difference method and the Newton-Raphson method are used simultaneously to solve the Reynolds equation In the clearance and the equation of motion for the piston. The tapered piston showed stable behaviors regardless of their initial eccentric conditions in the clearance and the reciprocating speed affect highly on the piston end trajectories. Therefore, the results of present study can be used other types fluid machineries.

• Proceedings of the Safety Management and Science Conference
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• 2009.11a
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• pp.223-229
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• 2009

The engine backfire leading to the damage to the intake system is observed in the mixer-type LPG engines. The hot spot flowing back into the intake manifold from the engine cylinder during the valve overlap period is known to give rise to the backfire. This backfire is known to be the main cause of the abrupt stop of the vehicle leading to the accidents on the streets. In this study, the cylinder pressure buildup at the later stage of combustion due to the prolonged burning is presumed to be the main cause of the backflow leading to the backfire. This is experimentally observed by creating the engine misfire using the ill-conditioned ignition systems.

• Proceedings of the KSR Conference
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• 1999.05a
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• pp.110-115
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• 1999

Experimental study is conducted to clarify the pneumatic characteristics of brake system for freight car. KNR(Korean National Railroad)'s freight cars have the laden-tare type control valve of brake system. But, laden-tare type control valve has some shortcomings to match the high speed freight car. Newly developed diaphragm type control valve is introduced to adopt freight car for speed-up. The test using the formated train set consisted of 21 cars is conducted to estimate the pneumatic braking efficiency of the mixed train set. From the results of experiment, the pressure characteristics of each brake cylinder show similar patterns qualitatively. But, in the case of release and brake application, quantitative pressure values of brake cylinder are different.

• Journal of Biosystems Engineering
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• v.35 no.6
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• pp.380-386
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• 2010

This study was carried out to develop soybean thresher which is able to reduce the soybean threshing damage in comparison to the conventional thresher. A threshing cylinder with different diameter of 480 and 384 mm at each end and with one quarter disc pegs of 60 mm radius was developed and attached to the prototype thresher. A conventional thresher which has a threshing cylinder with $\wedge$ type threshing pegs and same diameter of 480 mm at each end was used for comparative test. A series of comparative performance test was conducted using sun-yu and chung-ja soybean. For sun-yu bean, which is white and usually used for soybean paste and soy sauce, the ratio of damaged beans of prototype ranged 2-3% for 330-360 rpm which is recommended cylinder speed by manufacturer. The ratio of damaged beans of conventional thresher was 3-4% for the same range of cylinder speed. chung-ja beans with black color usually shows high damaged ratio compared with white beans, thus cylinder speed of 250-300 rpm is recommended by manufacturer to reduce the damaged ratio. For this range of cylinder speed, the damaged ratio of prototype was 1.3-1.4% and it was 2.7-6.1% for the conventional thresher. Thus prototype is able to reduce the damaged ratio 1.5-5.0% compared with conventional thresher. Prototype shows 0.4% of unthreshed soybean ratio for sun-yu bean in the optimum range of cylinder speed and it was 0.87% for the conventional thresher. For chung-ja bean, the ratio of unthreshed soybean was almost same for both prototype and conventional thresher with the value of 4.0%. The reason of high unthreshed soybean ratio for chung-ja bean compared sun-yu bean is due to the high seed moisture content of 29.11% which is much higher than that of the recommended.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.4
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• pp.302-310
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• 2013

As an initial step to develop a liquid hydrogen pump of piston type operated under cryogenic and high pressure, leakage and piston head shape for the piston pump were discussed with temperature and pressure. As the results, the leakage depended on correlation among density, viscosity, clearance area by the low temperature. In order to reduce the leakage, it was found that the air-tightness can be improved by minimizing contact surface between piston and cylinder, and also increasing pressure in-cylinder can reduce piston clearance. Among the proposed piston shapes, D type piston shape had the most air-tightness. D type piston had smaller contact surface than other piston shape and easier expansion of cup shape by pressure. The leakage of D type piston shape was found about 7%, compared with A type piston shape. But it was required that analyze about vapor lock by friction and wear resistance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.1
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• pp.105-116
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• 2003

The flow structure around the free end of a finite circular cylinder (FC) embedded in an atmospheric boundary layer (ABL) over open terrain was investigated experimentally with varying the free end shape. The experiments were carried out in a closed-return type subsonic wind tunnel. A finite cylinder with an aspect ratio (L/D) of 6 was mounted vertically on a long flat plate. The Reynolds number based on the cylinder diameter is about Re=7,500. The velocity fields near the FC free end were measured using the single-frame double-exposure PIV method. As a result, for the FC with a right-angled free end, there is a peculiar vortical structure, showing counter-rotating twin vortices near the FC free end. It is caused by the interaction between the entrained irrotational fluids from both sides of FC and the downwash flow from the FC free-end.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1075-1080
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• 2007

In order to reduce energy consumption, secondary controlled system has been applied to many types of equipments. In lifting equipments or press machines using hydraulic cylinder, a hydraulic transformer is used as a control component instead of a valve for motion control and a component for recovering potential energy of load. The transformer is a combination of a variable displacement pump/motor as a secondary controlled element and a fixed displacement pump/motor. In this paper the effect of transformer is studied. Multiple closed loop controllers with displacement feedback of variable pump/motor, speed feedback and position feedback of cylinder are used. The efficiency and energy consumption when cylinder is driven up and down is calculated by simulation. Simulation results show that considerable energy saving is achieved by choosing load ratio, circuit type and supply pressure.