• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.2
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• pp.128-135
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• 2008

EGR(exhaust gas recirculation) is considered as a most effective method to reduce the NOx emissions. But high EGR tolerance is always pursued not only for its advantages of the pumping loss reduction and fuel economy benefit in Gasoline-Hybrid engine. However, the occurrence of excessive cyclic variation with high EGR normally prevents substantial fuel economy improvements from being achieved in practice. Therefore, the optimum EGR rate should be carefully determined in order to achieve low fuel consumption and low exhaust emission. In this study, 2 liters gasoline engine with E-EGR system was used to investigate the effects of EGR on fuel efficiency, combustion stability, engine performance and exhaust emissions. With optimal EGR rates, the fuel consumption was improved by 4%. This improvement was achieved while a reduction in NOx emissions of 75% was accomplished. Increase of EGR gas temperature causes the charge air temperature to affect the knock phenomenon and moreover, the EGR valve lift changes for the same control signal.

• Journal of Biosystems Engineering
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• v.14 no.2
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• pp.85-93
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• 1989

This study was intended to develop the system which controls header height of combine automatically by means of sensing the difference between the header and the ground surface. A micro-computer was used for the controller. The sensing unit designed for the study was composed of potentiometer, oscillating link, and gage wheel. An electric-hydraulic circuit was driven by microcomputer to control header height of combine. Performance of the control system was tested by computer simulation, stationary operation of header, and traveling on the simulated ground.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.5B no.2
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• pp.181-188
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• 2005

In this paper, a DC smoothing filterless soft switching pulse modulated high frequency AC power conversion circuit connected to utility. frequency AC power source is proposed for consumer induction heating hot water producer, steamer and super heated steamer. The operating principle of DC link filterless utility frequency AC-high frequency AC (HF AC) power conversion circuit defined as high frequency cycloinverter is described, which can operate under a principle of ZVS/AVT and power regulation based on alternate asymmetrical PWM in synchronization with the utility frequency single phase AC positive or negative half wave voltage. The dual mode modulation control scheme based on high frequency PWM and commercial frequency AC voltage PDM for the proposed high frequency cycloinverter are discussed to enlarge its soft switching commutation operating range for wide HF AC power regulation. This high frequency cycloinverter is developed for high frequency IH Dual Packs Heater (DPH) type boiler used in consumer and industrial fluid pipeline systems. Based on the experiment and simulation results, this high frequency cycloinverter is proved to be suitable for the consumer use IH-DPH boiler and hot water producers. The cycloinverter power regulation and power conversion efficiency characteristics are evaluated and discussed.

• Journal of the Korean Society of Safety
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• v.27 no.5
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• pp.64-69
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• 2012

The concept of SIL is applied in the most of all standards relating to functional system safety. However there are problems for the people to apply SIL to their plants. as these standards don't include sufficient informations. In this regards, this paper will suggest the direction of SIL application and concept based on IEC 61508 and IEC 61511. A Safety Integrity Level(SIL) is the discrete level(one out of possible fours), corresponding to a range of the probability of an E/E/PE (Electric/Electrical/Programmable Electrical) safety-related system satisfactorily performing the specific safety functions under all the stated conditions within a stated period of time. SIL can be divided into the target SIL(or required SIL) and the result SIL. The target SIL is determined by the risk analysis at the analysis phase of safety lifecycle and the result SIL is calculated during SIL verification at the realization phase of safety lifecycle. The target SIL is determined by the risk analysis like LOPA(Layer Of Protection Analysis), Risk Graph, Risk Matrix and the result SIL is calculated by HFT(Hardware Fault Tolerance), SFF(Safe Failure Fraction) and PFDavg(average Probability of dangerous Failure on Demand). SIL is applied to various areas such as process safety, machinery(road vehicles, railway application, rotating equipment, etc), nuclear sector which functional safety is applied. The functional safety is the part of the overall safety relating to the EUC and the EUC control system that depends on the correct functioning of the E/E/PE safety-related systems and other risk reduction measures. SIL is applied only to the functional safety of SIS(Safety Instrumented System) in safety. EUC is the abbreviation of Equipment Under Control and is the equipment, machinery, apparatus or plant used for manufacturing, process, transportation, medical or other activities.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.291-300
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• 1999

Currently under development is an airborne auxiliary power unit with 100 Kw equivalent power, which is composed of a centrifugal compressor, a reverse annular combustor, and a radial turbine. Air-foil bearings are used in this power unit to eliminate the oil supplying system, which can reduce the system complexity and weight. The high speed generator is adopted as an electric power generation and engine starting system, which can also eliminate the reduction gear system. Not only electric power but also pneumatic power is provided by bleeding the compressed air This power unit is aimed for the multi-purpose use such as a primary power unit In the army weapon system, an auxiliary power and environmental control unit in a next-generation tank, and a smoke generating unit.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.684-685
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• 2006

In the present study, the powder metallurgical fabrication of $Bi_{0.4}Te_3Sb_{1.6}$ thermoelectric materials has been studied with specific interest to control the microstructure by the mechanical grinding process. The $Bi_{0.4}Te_3Sb_{1.6}$ thermoelectric powders with a various particle size distribution were prepared by the combination of the mechanical milling and blending processes. The specific electric resistivity of the $Bi_{0.4}Te_3Sb_{1.6}$ sintered bodies mainly depended on the orientation of the crystal structure rather than the particle size of the raw powders.

• 연구논문집
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• s.31
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• pp.89-99
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• 2001

This paper presents the modeling and analysis of dynamic characteristics of hydraulic snubber in electric power plant. The nonlinear state-space model of 14th order to describe the dynamics of the snubber was established by Simulink. The simulation results show that the hydraulic snubber reacts as like the conventional shock absolvers against the high pulse shock load. The snubber also shows the peculiar characteristics to the small step load, which temporarily lock the control valves up, however maintain same steady-state pressures of all internal chambers in the long run. Two case studies for the analysis of the snubber are addressed. Practical pulse testing method was also proposed to identify the frequency response of the snubber.

• Journal of Biosystems Engineering
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• v.39 no.1
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• pp.21-33
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• 2014

Background: Significant technological development and changes happened in the tractor industries. Contrariwise, the test procedures of the major standard development organizations (SDO's) remained unchanged or with a little modification over the years, demanding new tractor test standards or improvement of existing ones for tractor performance, safety, and comfort. Purpose: This study focuses on reviewing the research trends regarding performance, safety and comfort evaluation of agricultural tractors. Based on this review, few recommendations were proposed to revise or improve the current test standards. Review: Tractor power take-off power test using the DC electric dynamometer reduced human error in the testing process and increased the accuracy of the test results. GPS signals were used to determine acceleration and converted into torque. High capacity double extended octagonal ring dynamometer has been designed to measure drawbar forces. Numerical optimization methodology has been used to design three-point hitch. Numerous technologies, driving strategies, and transmission characteristics are being considered for reducing emissions of gaseous and particulate pollutants. Engine emission control technology standards need to be revised to meet the exhaust regulations for agricultural tractors. Finite Element Analysis (FEA) program has been used to design Roll-Over Protective Structures (ROPS). Program and methodology has been presented for testing tractor brake systems. Whole-body vibration emission levels have been found to be very dependent upon the nature of field operation performed, and the test track techniques required development/adaptation to improve their suitability during standardized assessment. Emphasizes should be given to improve visibility and thermal environment inside the cab for tractor operator. Tractors need to be evaluated under electromagnetic compatibility test conditions due to large growing of electronic devices. Research trends reviewed in this paper can be considered for possible revision or improvement of tractor performance, safety, and comfort test standards.

• Journal of Biosystems Engineering
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• v.42 no.1
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• pp.56-61
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• 2017

Purpose: High energy requirement and long cooking time are limiting consumption of pigeon pea (Cajanus cajan), a nutritious food. This study was performed to estimate energy and time demand by different methods of cooking pigeon pea. Methods: Pigeon pea (150 g) was soaked in 2.0 L of water at ambient temperature ($29{\pm} 2^{\circ}C$) to determine hydration behavior. Cooking experiments were conducted using aluminum and pressure-cooking pots. Efficiency of cooking was evaluated using four types of cooking appliances (kerosene, liquefied petroleum gas (LPG), electric, and charcoal stoves). Normal (continuous heating until the food was satisfactorily cooked) and control (controlling the energy input to closely match the actual energy required) cooking were conducted. Energy requirement and duration of cooking were determined using standard procedures. Results: Soaking increased moisture content from 11.99 to 30.01% in 90 min, while water absorption rate decreased with soaking duration. In cooking 150 g of pigeon pea using kerosene stove, presoaked normal pressure-pot cooking method consumed the least energy (10 800 kJ) and time (205 min), while unsoaked normal cooking consumed the highest energy (18 450 kJ) and time (336 min). Using LPG stove, unsoaked normal cooking method required the highest energy (52 470 kJ), while presoaked control pressure-pot required the least energy (14 405 kJ). For electric stove, the lowest energy (15 560 kJ) and shortest duration (105 min) were recorded during control cooking of presoaked sample in the pressure-pot. Conclusions: Control cooking was not practicable using charcoal stove. Generally, kerosene stove consumed the least energy, while electric stove was found to have the shortest duration of cooking.

• Proceedings of the KIPE Conference
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• 2002.11a
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• pp.7-11
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• 2002

This paper proposes an APF(Active Power Filter) with WRIM(Wounded Rotor Induction Motor) controlled by sliding mode which can compensate harmonic currents generated in a power system. As non-linear loads increase gradually in industry fields, harmonic current generated In the electric power network system also increases. Harmonic current makes a power network current distorted and generates heat, vibration and noise In the power machinery, Many approaches have been applied to compensate harmonic currents generated in the power system. Among various control strategy, in this paper, a sliding mode controlled systems is designed and evaluated. This is a flywheel compensator based on secondary excitation of WRIM(wounded rotor induction motor) with SMC(sliding mode controller). The proposed system uses a flywheel as an energy storage device. The designed control scheme is verified through simulation.