• 한국기계가공학회지
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• 제8권2호
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• pp.83-89
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• 2009

An air-fuel ratio control is essential in reducing hazardous exhaust emissions from a compressed natural gas(CNG) engine, and can be accomplished by accurate control of gas injection flow. In this study, theoretical research was conducted on injection characteristics of a solenoid gas injector, and injection experiments for calibration and analysis were performed. Various factors for gas injection flow such as injection pressure, gas temperature, and supply voltage are studied. A dynamic flow equation of the natural gas was proposed on the basis of flow dynamics theories and results of the injection experiment. The verification of the dynamic flow equation of the solenoid injector was carried out with a large CNG-engine applied to an urban bus. Air-fuel ratio control experiments were conducted in both steady and transient state. Results of injection experiments for the solenoid injector and the CNG-engine was proved the control method proposed herein to be effective.

• Journal of Biosystems Engineering
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• 제21권2호
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• pp.155-166
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• 1996

A direct injection sprayer was designed using the concepts of injection mixing and total flow control, flowrate-based system compensating for the variation of forwarding speed. A metered rate, proportionally to the actual diluent flow rate, of a tracer chemical was injected directly into the diluent stream. The injection of chemical may improve the precision and safety of chemical application process. The control system was evaluated for the variables of the control interval, tolerances and sensitivities of flow regulation valve and injection pump. Performance of the system was assessed as that the response time of flow rate, response time of injection rate, absolute steady state error, and the coefficient of variance(C.V.) of concentration were 8.5 and -0.53 seconds, 0.067 lpm(0.8%) and 3.15%, respectively, at optimal parameters of control interval of 1.0 sec, fast sensitivity of flow regulation valve, medium sensitivity of injection pump and medium tolerance of flow rate. Performance of the system can be improved by increasing the sensitivity of flow regulating valve and employing a high resolution velocimeter, such as Doppler radar.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.142-147
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• 2004

The flow in the LOX manifold of liquid rocket has been investigated using a CAE technique with an objective of economical modeling of injection holes in order to reduce the overall computational cost of flow analysis during the optimal rocket design procedure. The computational geometry is very close to that of the actual rocket design and the flow condition through the injection holes resembles that in the actual manifold of the liquid rocket. The result shows that the flow in the plane just above the injection holes is not uniformly distributed in terms of pressure and mass flow rate and this is attributed to the large-scale flow patterns present the LOX manifold. Thus, the flow physics should be understood correctly before making any attempt to model the injection holes. In the present study, several boundary conditions which were designed to effectively replace the presence of injection holes have been tested and it was found that a simple modeling can be possible by mimicking the actual geometry of the injection holes. By using this simple injection hole modeling, it was able to obtain about 30% reduction in computational cost but it was still able to reproduce the flow patterns correctly. Also the flow has been analyzed after incorporating a couple of different types of pre-distributors in LOX manifold and the effect of those will be discussed.

• 한국공작기계학회논문집
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• 제11권4호
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• pp.44-53
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• 2002

Injection molding process factors such as molding temperature, injection pressure, flow rate and flow velocity, must be controlled properly in filling and packing phases in the injection molding process. In this study, effects of these factors on the injection molding were investigated through the flow analysis for the filling and packing phases. Molding troubles like flow mark weld line, sink ma가 short shot and warpage car be caused by these injection molding process factors. Among them the short shot was caused by the fact that the packing pressure could not reach properly to the filling end part in the packing phase and hence the flow rate could not be supplied to the full. In addition as the flow rate for the volumetric shrinkage during the f개zen phase could not be supplied Properly by the packing pressure, the short shot appeared. Here, the volumetric shrinkage reduced with increasing the packing pressure and also the warpage of molded part increased with increasing the packing Pressure.

• 소성∙가공
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• 제12권8호
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• pp.738-743
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• 2003

The major problems of a plastic injection mould can be devided into two kinds, one is in mould another in injected parts. Most of defects of the former comes from mould design, such as, structure and working. The latter are weld line, warpage, sink mark, burning, flow mark, scratching, shading, black hole and so on. Most of problems in injection molding are difficult to find the reason because of complexity. The purpose of this paper is to improve the quality of plastic injection mould and parts with inquiring the counter plan and analizing troubles of the part of Flat TV Front Cover by flow control method and gas-assisted injection moulding. For minimizing defects of the injection moulded parts, computer aided simulation method for injection mould filling was used. Based on these numerical results, the guidelines of mould design and injection processing condition were established. As a result, the improvement of quality, such as minimizing surface defects of injection moulding parts and troubles in mould was achieved.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 춘계학술대회 논문집
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• pp.112-118
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• 2002

Injection molding process factors such as molding temperature, injection pressure, flow rate and flow velocity, must be controlled properly in filling and packing phases in the injection molding process. In this study, effects of these factors on the injection molding were investigated through the flow analysis fur the filling and packing phases. Molding troubles like flow mark, weld line, sink mark, short shot and warpage can be caused by these injection molding process factors. Among them, the short shot was caused by that the packing pressure could not reach properly to the filling end part in the packing phase and hence the flow rate could not be supplied to the full. In addition, as the flow rate for the volumetric shrinkage during the frozen phase could not be supplied properly by the packing pressure, the short shot appeared. Here, the volumetric shrinkage reduced with increasing the packing pressure and also the warpage of molded part increased with increasing the packing pressure.

• 대한기계학회논문집
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• 제16권4호
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• pp.795-802
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• 1992

본 연구에서는 일정한 각도의 분사를 갖는 평씨일(plain seal)에 대하여 각 인자들이 누수성능에 미치는 영향을 수치적으로 조사하였다. 인자들로는 축방향 레 이놀즈수, 축회전속도, 분사의 유입속도, 간극비, 분사의 위치 및 유입각 등이 고려되 었다.

• 한국기계가공학회지
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• 제7권3호
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• pp.25-29
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• 2008

In this paper, we design internal space in plunger-type low pressure vacuum injection molding machine from numerical study. And we study characteristic of viscoelastic flow for searching injection molding condition. Then the flow analysis was performed using the CAE S/W. The result shows optimal value of nozzle and hole in injection chamber. And we investigated qualitatively relationship between injection pressure and injection mass flow with variable shear rate

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.375-376
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• 2006

Thermoplastic elastomer(TPE) can be molded by conventional injection molding. Therefore TPE injection molding could be analyzed by commercial flow analysis software. However there are a little of gaps on CAE simulation results and practical molding. In this study, the properties of TPE were measured and applied to CAE simulation for comparing the simulation flow pattern and real flow pattern. The pattern that was controlled by injection time was match. The pattern that was controlled by injection stroke and rate was not match.

• 산업기술연구
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• 제20권B호
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• pp.45-53
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• 2000

A numerical study is done on the thrust vector control using gaseous secondary injection in the rocket nozzle. A commercial code, PHOENICS, is used to simulate the rocket nozzle flow. A $45^{\circ}-15^{\circ}$ conical nozzle is adopted to do numerical experiments. The flow in a rocket nozzle is assumed a steady, compressible, viscous flow. The exhaust gas of the rocket motor is used as an injectant to control the thrust vector of rocket at the constant rate of secondary injection flow. The injection location which is on the wall of rocket is chosen as a primary numerical variable. Computational results say that if the injection position is too close to nozzle throat, the reflected shock occurs. On the other hand, the more mass flow rate of injection is needed to get enough side thrust when the injection position is moved too far from the throat.