• 한국자동차공학회논문집
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• 제6권6호
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• pp.202-209
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• 1998

For development of SDI(Spark-ignited Direct Injection) engine, stratified mixture formation with adequate strength at spark plug was required in wide range of engine operating conditions. So, spray structure under high ambient pressure and spray distribution after impingement on piston bowl in motoring engine was visualized by using laser equipments. Also, incylinder bulk flow structure was measured by using PIV (Paiticle Image Velocimetry) system. Counter-rotating tumble port and bowl piston was found effective to conserve bulk motion directed to spark plug in compression stroke. In addition, mask attached near valve seat in intake port was proposed to attenuate conventional tumble component and enhance counter-rotating tumble component.

• 한국신뢰성학회:학술대회논문집
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• 한국신뢰성학회 2000년도 추계학술대회
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• pp.75-86
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• 2000

본 연구사례는 댐 수문용 대형유압실린더(Piston Diameter :630mm, Stroke:8.3m, weight :30ton, Retraction Force:450ton)의 신뢰성평가를 위한 검토과정에서 제기된 문제를 보완하여, 평가규격을 정립하고, 시험장비를 구축하여, 초대형 유압실린더의 신뢰성 평가를 실시한 사례에 대하여 정리한 것이다.

• 오토저널
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• 제10권5호
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• pp.33-41
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• 1988

내연기관에서 crankshaft는 piston에 작용하는 수직 gas force 및 관성력을 회전력으로 바꾸어 주는 역할을 한다. 그러므로 engine작동중 높은 부하를 반복적으로 받기 때문에 이에 견딜 충분한 stiffness를 유지해야 한다. Engine의 stroke 운동시에 gas force와 관성력이 변하고 crankshaft의 형상이 복잡하므로 실제적으로 응력계산은 간단하지 않다. 여기에서는 crankshaft에 작용하는 하중과 반력을 계산하고 crankshaft의 stress 및 safety factor를 계산하여 crankshaft를 설계하는 방법을 설명하고자 한다. 근래 FEM에 의한 stress analysis를 많이 수행하나, loading condition을 주기 위해서는 classical method에 의해서 구할 수 있다.

• Journal of Advanced Marine Engineering and Technology
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• 제32권8호
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• pp.1129-1140
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• 2008

Many turbulence models have been developed in order to analyze the flow characteristics in an engine cylinder. Watkins introduced k-${\varepsilon}$ turbulence model for in-cylinder flow, and Reynolds modified turbulence dissipation rate by applying rapid transformation theory, Wu suggested k-${\varepsilon}-{\tau}$ turbulence model in which length scale and time scale are separated to introduce turbulence time scale, and Orszag proposed k-${\varepsilon}$ RNG model. This study applied the models to in-cylinder flow induced by intake valve and piston moving. All models showed similar flow fields during early stage of intake stroke. At the end of compression stroke, ${\kappa}-{\varepsilon}$ Watkins, ${\kappa}-{\varepsilon}$ Reynolds and ${\kappa}-{\varepsilon}$ RNG predicted well second and third vortex, especially ${\kappa}-{\varepsilon}$ RNG produced new forth vortex near central axis at the lower part of cylinder which was not predicted by the other models.

• 유공압시스템학회논문집
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• 제7권1호
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• pp.11-19
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• 2010

A gas-assisted hydraulic breaker uses both hydraulic and pneumatic energies and the appropriate balance between them mostly effects its performance. Mathematical modeling of the breaker is established and verified by experiment. Through sensitivity analysis using AMESim, the key design parameters are selected, which mostly affect the performance of the breaker. Taguchi method is used to optimize the key design parameters to maximize the output power for long and short strokes through simulation. As the result, the output power as well as the impact energy are increased significantly compared with the existing design. The pressure pulsation in the supply line is reduced to a tolerable level and the dynamic characteristics of the piston displacement is also improved by the optimization.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 추계학술대회 논문집
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• pp.235-241
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• 1998

Flow characteristics of a compressible gas flow through a rotating disc-type rotary valve are investigated experimentally under various conditions. It is known that the mass flow rate through poppet valves of 4-stroke cycle engines and through piston valves of 2-stroke cycle engines decrease with increase in engine speed. Rotary valve is one means by which air maybe made to flow intermittently through a pipe. In this paper a exhaust system simulator of engine was used to experimentally analyzer the decrease inflow rate at high rotation speeds and to determine what variables, other than rotational speed, give rise to the observed behaviour. These variables have been included in an empirical equation which is representative of the measured flow characteristics.

• 대한기계학회논문집B
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• 제32권11호
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• pp.878-883
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• 2008

The spray characteristics of a high pressure 6-hole injector were examined in a single cylinder optical direct injection spark ignition (DISI) engine. The effects of injection timing, in-cylinder charge motion, fuel injection pressure and coolant temperature were investigated using the 2-dimensional Mie scattering technique. It was confirmed that the in-cylinder charge motion played a major role in the fuel spray distribution during the induction stroke while the propagation of fuel spray was restrained during the compression stroke by the increasing pressure and the upward moving piston. In additions, it was confirmed that the liquid fuel droplets existing at the sprays edges were vaporized by the increase of the coolant temperature.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
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• pp.209-211
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• 2015

Evaporation characteristics of a single droplet of carbon nanofluids were investigated in a rapid compression machine(RCM). n-Heptane and carbon black N990 were used to synthesize the carbon nanofluids. RCM is an experimental set-up to simulate a single compression stroke of reciprocating engine. Temperature and pressure in a reaction chamber were measured during the compression stroke. After the piston reaches top dead center(TDC), temperature and pressure decreased due to the heat loss at wall. In that process, a single droplet of carbon nanofluids underwent unsteady condition. A single droplet was put at the center of reaction chamber. Thermocouple whose tip is $50{\mu}m$ was used not only to measure transient bulk temperature, but also to suspend the droplet. The picture of single droplet was taken using high speed camera with a frame rate of 500 fps. From those pictures, the droplet diameter was measured by visual basic program.

• Coupled systems mechanics
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• 제5권2호
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• pp.191-201
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• 2016

Coupled structures are widely seen in civil and mechanical engineering. In coupled structures, monitoring the translational motion of its key components is of great importance. For instance, some coupled arms are equipped with a hydraulic piston to provide the stiffness along the piston axial direction. The piston moves back and forth and a distance sensing system is necessary to make sure that the piston is within its stroke limit. The measured motion data also give us insight into how the coupled structure works and provides information for the design optimization. This paper develops two distance sensing systems for coupled structures. The first system measures distance with ultrasonic sensor. It consists of an ultrasonic sensing module, an Arduino interface board and a control computer. The system is then further upgraded to a three-sensor version, which can measure three different sets of distance data at the same time. The three modules are synchronized by the Arduino interface board as well as the self-developed software. Each ultrasonic sensor transmits high frequency ultrasonic waves from its transmitting unit and evaluates the echo received back by the receiving unit. From the measured time interval between sending the signal and receiving the echo, the distance to an object is determined. The second distance sensing system consists of a wire draw encoder, a data collection board and the control computer. Wire draw encoder is an electromechanical device to monitor linear motion by converting a central shaft rotation into electronic pulses of the encoder. Encoder can measure displacement, velocity and acceleration simultaneously and send the measured data to the control computer via the data acquisition board. From experimental results, it is concluded that both the ultrasonic and the wire draw encoder systems can obtain the linear motion of structures in real-time.

• 동력기계공학회지
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• 제13권4호
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• pp.11-17
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• 2009

This paper deals with the effects of pulsating flow on volumetric efficiency, which may be generated during the gas exchange procedure, due to piston motion, valve event on intake and exhaust stroke and unsteady flow of turbocharger of a three-cylinder four stroke turbo-charged diesel engine. Consequently, volumetric efficiency affects significantly the engine performance; torque characteristics, fuel economy and further to emission and noise level. As the expansion ratio became larger the engine speed varies and torque increases, the pressure pulsation in an exhaust gas pipe acts as an increasing factor of intake air charging capacity totally. The phase and amplitude of pressure pulsation in the intake system only affects volumetric efficiency favorably, if it is well matched and tuned effectively to the engine. Thus, to verify the exact phase and amplitude of the pressure variation is the ultimate solution for the air-flow ratio assessment in the intake stroke. Some experimental results of pressure diagrams in the intake pipe and gas-flow of turbine in-outlet are presented, under various kinds of operating condition.