• 한국자동차공학회논문집
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• 제10권4호
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• pp.23-32
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• 2002

Combustion and flame propagation characteristics of the liquid phase LPG injection (LPLI) engine were investigated in a single cylinder optical engine. Lean bum operation is needed to reduce thermal stress of exhaust manifold and engine knock in a heavy duty LPG engine. An LPLI system has advantages on lean operation. Optimized engine design parameters such as swirl, injection timing and piston geometry can improve lean bum performance with LPLI system. In this study, the effects of piston geometry along with injection timing and swirl ratio on flame propagation characteristics were investigated. A series of bottom-view flame images were taken from direct visualization using an W intensified high-speed CCD camera. Concepts of flame area speed, In addition to flame propagation patterns and thermodynamic heat release analysis, was introduced to analyze the flame propagation characteristics. The results show the correlation between the flame propagation characteristics, which is related to engine performance of lean region, and engine design parameters such as swirl ratio, piston geometry and injection timing. Stronger swirl resulted in foster flame propagation under open valve injection. The flame speed was significantly affected by injection timing under open valve injection conditions; supposedly due to the charge stratification. Piston geometry affected flame propagation through squish effects.

• 한국분무공학회지
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• 제26권2호
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• pp.81-87
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• 2021

This study was performed to calculate the swirl ratio of a diesel engine intake port by a 1D computer simulation under actual engine operating conditions. The swirl ratio of the intake port was simulated according to the change of the engine speed during the operation of the motoring without fuel injection. The swirl ratio of the intake port was simulated according to changes in the crank angle during the four-cycle operation of intake, compression, expansion and exhaust. The swirl ratio represented by the three regions of the piston, center and squish was simulated. Among the three regions, the piston-region swirl ratio is important for effective air-fuel mixing in the engine cylinder. In particular, it was confirmed during the simulation that the piston swirl ratio before and after the compression top dead center (TDC) point when fuel is injected in the DI diesel engine can have a significant effect on the mixing of air and fuel. It was desirable to set the average piston swirl ratio over a crank angle section before and after compression TDC as the representative swirl ratio of the cylinder head intake port according to the change of the engine speed.

• 대한기계학회논문집A
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• 제36권11호
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• pp.1441-1446
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• 2012

유압피스톤모터는 정압베어링부분의 마찰손실과 용적손실, 기구적 운동부분의 마찰손실, 오일의 관로저항에 의한 압력저하, 압축성에 의한 체적손실 그리고 하우징 오일 처닝(churning) 손실 등이 있다. 이러한 손실 중에서 일정한 틈새의 유막(oil film, $8{\sim}15{\mu}m$)으로 고속 회전하는 피스톤 슈(piston shoe)와 슈 플레이트(shoe plate) 사이 정압베어링 부분의 마찰 및 용적손실이 유압모터의 전체효율을 좌우 한다. 본 연구에서는 최고압력 35MPa, 최고회전수 2500rpm, 배재용적 320cc/rev급 2속(2-speed) 초대형 굴삭기의 주행모터용 유압피스톤모터를 대상으로 정압베어링비가 유압모터의 전 효율에 미치는 영향을 실험적으로 분석하였다.

• 한국자동차공학회논문집
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• 제8권6호
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• pp.79-86
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• 2000

The effects of recirculated exhaust gas on the wears of piston and piston rings were investigated by the experiment with a two-cylinder, four cycle, indirect injection diesel engine operating at an engine load of 75% and an engine speed of 1600 rpm. For the purpose of comparison between the wear rates of two cylinders with and without EGR, the recirculated exhaust gas was sucked into one of two cylinders after the soot contenets in exhaust emissions were removed by an intentionally designed cylinder-type scrubber equipped with 6 water injectors(A water injector has 144 nozzles of 1.0 mm diameter), while only the fresh air was inhaled into the other cylinder. These experiments were carried out on the fuel injection timing fixed at 15.3$^{\circ}$ BTDC. It was found that the wear rate of piston skirt with EGR increased a little bit, but the piston head diameter increased, rather than decreased, owing to soot adhesion and erosion wear, and especially larger with EGR, and that the wear rates of the top and second piston ring(compression ring)thickness with EGR were more than twice the wear rate of top ring in case of no EGR, but the wear rate of oil rings thickness without EGR increased greater than that with EGR.

• Journal of Biosystems Engineering
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• 제17권4호
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• pp.396-403
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• 1992

In order to operate a combine harvester at the optimum conditions and maximum performance, a forward speed control system(FSCS) was designed and develped. The FSCS consisted of engine, continuously variable V-belt transmission, threshing unit, traveling unit, detecting unit, and controller. Each components of the system were mathematically modeled. By a computer simulation, the effects of control parameters such as hydraulic piston speed, speed ratio, dead band of engine speed on the system performance were analysed, and the optimum control conditions were identified. The system appeared to be the most stable at the hydraulic piston speed of 10.6mm/s and the speed ratio of 0.4. The proper dead band of engine speed appeared to be 30rpm through the simulation and verification tests.

• 한국산학기술학회논문지
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• 제16권12호
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• pp.8274-8283
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• 2015

텔레비전의 가스 스프링은 롱 스트로크 (200 ~ 300mm, TV 상승 변위) 하에서 작동 할 때 피스톤 속도의 제어가 가능하다. 이 원리에 의해서 사용자는 높낮이 조절이 가능하다. 먼저 피스톤의 흐름 해석을 수행하였다. 정확한 관형 단면을 위한 피스톤 속도 조절기술을 조사하였다. 유동률 제어 및 높낮이 작용을 위한 피스톤 구조를 제안되었다. 본 연구는 대형 텔레비전 스탠드를 통해 50 인치 이상 TV의 가스 스프링의 개발을 위한 것이다. 최적 피스톤 로드 제어를 위한 중공축(외경 19.9mm, 내경 13.9mm)에 질소 개스(0.3m/s)를 주입하였다. 그 결과, 유동율이 증대함에 따라 피스톤 로드의 압력강하는 외력의 변화 없이 증대되었다. 결과적으로, 가스스프링을 통한 변위의 제어는 가능하다.

• 한국산학기술학회논문지
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• 제16권11호
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• pp.7745-7753
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• 2015

텔레비전의 가스 스프링은 롱 스트로크 (200 ~ 300mm, TV 상승 변위) 하에서 작동 할 때 피스톤 속도의 제어가 가능하다. 이 원리에 의해서 사용자는 높낮이 조절이 가능하다. 먼저 피스톤의 흐름 해석을 수행하였다. 정확한 관형 단면을 위한 피스톤 속도 조절기술을 조사하였다. 유동률 제어 및 높낮이 작용을 위한 피스톤 구조를 제안되었다. 본 연구는 대형 텔레비전 스탠드를 통해 50 인치 이상 TV의 가스 스프링의 개발을 위한 것이다. 최적 피스톤 로드 제어를 위한 중공축(외경 19.9mm, 내경 13.9mm)에 질소 개스(0.3m/s)를 주입하였다. 그 결과, 유동율이 증대함에 따라 피스톤 로드의 압력강하는 외력의 변화 없이 증대되었다. 결과적으로, 가스스프링을 통한 변위의 제어는 가능하다.

• Journal of Mechanical Science and Technology
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• 제20권3호
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• pp.358-365
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• 2006

The hydraulic pump of an Electro-hydrostatic Actuator should be able to quickly feed large volume of oil into hydraulic cylinder in order to reduce the response time. On the other hand, it should be also able to precisely dispense small amount of oil through low-speed operation so that the steady state position control error of the actuator can be accurately compensated. Within the scope of axial piston type hydraulic pumps, this paper is focused on the investigation how the surface treatment of their cylinder barrel with TiN plasma coating can contribute to the reduction of the friction and wear rate of valve plate in the low-speed range with mixed lubrication. The results showed that the friction torque of the valve plate mated with a TiN coated cylinder barrel could be reduced to 22% of that with an uncoated original one when load pressure was 300 bar and rotational speed 100 rpm. It means that the torque efficiency of the test pump was expected to increase more than 1.3% under the same working condition. At the same time, the wear rate of the valve plate could be reduced to $40\sim50%$.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제31회 춘계학술대회
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• pp.106-113
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• 2000

A pump which is a fundamental device in a hydraulic system affects on overall system performance to a great deal. Such problems as leakage and solid friction loss become important in field applications, especially for the case of operation under high pressure and at high speed. So the research on this kind of subjects is necessary to improve the performance of hydraulic devices. A high pressure radial piston pump is analyzed here, which has a stationary cylinder block. It pumps hydraulic fluid by letting camring push a piston in a cylinder. Fluid leaks between the piston and cylinder so that it deteriorates the pump efficiency. Furthermore, the piston happens to touch the cylinder wall to increase the friction loss and wear. In this research, by means of FDM, volumetric, mechanical and overall efficiencies are observed by varying several design Parameters and operation conditions. Design values or their trends are presented to improve these efficiencies.

• Tribology and Lubricants
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• 제16권4호
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• pp.259-265
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• 2000

Pump which is the fundamental device in the hydraulic system affects on overall system performance to a great deal. Such problems as leakage and solid friction loss become important in field applications, especially for the case of operation under high pressure and at high speed. So the research on this kind of subjects is necessary to improve the performance of hydraulic devices. A high pressure radial piston pump is analyzed here, which has a stationary cylinder block. It pumps hydraulic fluid by letting camring push a piston in a cylinder. Fluid leaks between the piston and cylinder so that it deteriorates the pump efficiency. Furthermore, the piston happens to touch the cylinder wall to increase the friction loss and wear. In this research, by means of FDA, volumetric, mechanical and overall efficiencies are observed by varying several design parameters and operation conditions. Design values or their trends are presented to improve these effciencies.