• 한국자동차공학회논문집
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• 제10권5호
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• pp.107-113
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• 2002

LPG has been well known as a clean alternative fuel for vehicles. Recently, several LPG engines for heavy duty vehicles have been developed, which can replace some diesel engines that are one of the main sources for air pollution in the urban area. Because cylinder bore of heavy duty LPG engine is larger than that of gasoline, the study of knock characteristics of LPG engine are needed. In this study, the knock characteristics were investigated with various engine speed, air excess ratios and LPG fuel compositions. Experimental results indicated that the Knock occurrence probability decreases with increasing engine speed and propane fraction of fuel. The Knock occurrence probability is highest at excess air ratio of 1 and decreases as the mixture strength became leaner.

• 영재교육연구
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• 제25권1호
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• pp.37-58
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• 2015

본 연구는 개념적 혼란이 지속되고 있는 융합교육의 특성을 규명하기 위하여 융합교육의 현장경험을 가진 교사 19명을 대상으로 델파이 연구를 수행하였다. 총 3차의 델파이 연구가 실시되었으며, 융합교육의 특성으로서 핵심요인과 기대효과를 도출하였다. 융합교육의 전제 조건인 핵심요인은 학습자의 다양한 질적 경험을 위해 교육내용과 교육방식의 개방적이고 융통적인 활용을 강조하는 '교육설계', 교사, 교사-동료 간, 교사-학습자 간의 관계 속에서 발휘되는 교사의 역량을 의미하는 '교사전문성', 다양한 교육주체의 심리적 지원을 통해 융합교육을 가능하도록 하는 '교육환경'으로 유형화되었다. 융합교육의 기대효과는 '학습자의 인지적 특성', '학습자의 정의적 특성', '교사 및 교육체제' 차원에서의 변화를 포함하였으며, 융합교육이 교육 본연의 가치를 실현하는 하나의 틀로서 인식되었다. 본 연구에서 융합교육은 다수의 일반적인 학습자를 대상으로 한 교육적 가치 실현을 지향하며, 다양한 교육내용과 교육방식을 적용하고 교사의 전문성을 비롯한 관련 교육주체의 심리적 요인이 중요한 핵심요인으로 다루어진다는 특성을 나타냈다. 연구의 결과는 융합교육의 실체를 다각적인 이해의 틀을 가지고 교육 현장의 맥락에서 확인하였다는 점에서 의의를 갖는다.

• 한국자동차공학회논문집
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• 제14권2호
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• pp.114-120
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• 2006

The basic effects of hydrogen addition for engine performance and emission were investigated in single cylinder research engine. Seven commercial injectors were tested to choose a suitable injector for hydrogen injection prior to its engine implementation. The hydrogen fuel leakage and flow rate were evaluated for each injector and KN3-1(Keihin, CO.) showed the best performance for hydrogen fuel. At the higher excess air ratio(${\lambda}=1.7$, 2.0), the better combustion stability was found with hydrogen addition even though its effect was small at lower excess air ratio (${\lambda}=1.0$, 1.3). Stable operation of the engine was even guaranteed at ${\lambda}=2.0$, if the amount of hydrogen gas was near 15% of total energy. In the lean region, ${\lambda}>1.3$, thermal efficiency was improved slightly while it was not clearly observed at ${\lambda}=1.0$, 1.3. It is considered that, in some cases, high temperature environment due to hydrogen combustion caused further heat loss to surroundings. Except for ${\lambda}=1.0$, with larger amount of hydrogen addition, CO was reduced drastically but it was emitted more at the leaner region. Nitric oxides(NOx) was increased a little more with hydrogen addition at ${\lambda}=1.0$, 1.3. However, at ${\lambda}>1.3$ its relative amount of emission was low. In addition, the amount of NOx was continuously decreased with hydrogen addition, but, at ${\lambda}=2.0$ the amount of NOx was lowered to 1/100 of that of ${\lambda}=1.0$. THC emission was significantly increased as air/fuel ratio was raised to leaner region due to misfire and partial burn.

• Journal of Information Technology Applications and Management
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• 제15권1호
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• pp.99-116
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• 2008

This study explores the impacts of e-learning system characteristics on learner committment and satisfaction by surveying the firms utilizing e-learning systems for learning. In the study, we have, first, drawn the key factors and instruments to measure e-learning system characteristics through intensive literature review. Second, we have investigated whether the characteristics contribute to increasing learner's commitment and satisfaction. Finally, we have examined the mediating effect of learner's commitment between the characteristics of e-learning system and learner satisfaction. We have conducted a survey on the employees having experience in using e-learning systems for learning, and collected a total of 93 responses. The results of a statistical analysis show the following: First, expression and interaction affect the learner's commitment. The results indicate that a learner should engage in e-learning and ultimately be more committed on it when there is a coherence in design and organization of learning contents, and when the system offers various multimedia options including audio, sound, image, graphics, etc. Second, leaner's commitment leads to higher learning satisfaction. Finally, our results show that the commitment plays a mediating role between learner characteristics (expression, control, and trust) and learner satisfaction.

• Journal of Mechanical Science and Technology
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• 제17권9호
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• pp.1371-1379
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• 2003

The effects of change in injection pressure on spray structure in high temperature and pressure field have been investigated. The analysis of liquid and vapor phases of injected fuel is important for emissions control of diesel engines. Therefore, this work examines the evaporating spray structure using a constant volume vessel. The injection pressure is selected as the experimental parameter, is changed from 22 MPa to 112 MPa using a high pressure injection system (ECD-U2). Also, we conducted simulation study by modified KIVA-II code. The results of simulation study are compared with experimental results. The images of liquid and vapor phase for free spray were simultaneously taken by exciplex fluorescence method. As experimental results, the vapor concentration of injected fuel is leaner due to the increase of atomization in the case of the high injection pressure than in that of the low injection pressure. The calculated results obtained by modified KIVA-II code show good agreements with experimental results.

• 한국자동차공학회논문집
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• 제10권2호
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• pp.73-79
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• 2002

The NO emissions at the exhaust manifo1d were investigated with a fast NO analyzer to investigate the cycle-by-cycle variations on NO emissions level and the dependence of NO emissions on combustion. The measurement was performed with a part load condition with respect to the mixture ratios and the changes in loads at 1800rpm. The averaged values were obtained during 200 cycles. We found that there is characteristic pattern in 70 emissions from exhaust port and it was possible to set a representative value with the data sampled during specific period. As the load increased, the characteristics of NO emissions were more dependent on combustion pressures. It was also analyzed that the correlation between combustion pressures and NO emissions for different equivalence ratios tends to increase as the mixture goes leaner, Furthermore, this correlation for the lean mixture near the lean limit seemed to be kept.

• Journal of Advanced Marine Engineering and Technology
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• 제29권2호
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• pp.154-160
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• 2005

The result of combustion experiment by using the methanol-gasoline blended fuel showed that the supplying pressure appeared the maximum pressure between equivalent rate 1.1 and 1.2. and the evaporation of the fuel has been known to have been greatly influenced by surrounding temperature and the combustion chamber temperature after being injected from the injector And it is confirmed that the rate of evaporation had been suddenly dropped according to the temperature in the combustion chamber though the injected foe) had been fully evaporated Such tendency has visibly appeared when the zone is leaner. and we recognize that the rich fuel supply is needed in the operation of cold operating.

• Journal of Advanced Marine Engineering and Technology
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• 제17권3호
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• pp.60-69
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• 1993

The speed control associated with dc servo motors for direct-drive applications of mobile robot is considered in this study. Robot is moved by power wheeled steering of two dc servo motors mounted to it. In order to cooperate with micro-computer and to achieve the high-performance operation of dc servo motor, speed control system is composed of a digital Phase Locked Loop and H-type drive circuit. And the motor is driven by Pulse Width Modulations. In controlling PWM, it is modified to compose of H-type drive circuit with feedback diodes and switching transistor and design of control sequence so that it may show linear characteristics. As a result, speed characteristics of motor showed linear features. In order to get data on design of PLL control system, the parameters of 80[W[ motor & robot device is measured by simple software control. The PLL speed control system is schemed and designed by leaner drive circuit and measured parameters. A complete speed control system applied to 80[W] dc servo motor showed good linearity, stability and high response. Also, it is verified that the PLL speed control system has good compatibility as a mobile robot driver.

• 한국자동차공학회논문집
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• 제14권3호
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• pp.1-9
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• 2006

Recently, there has been an interest in premixed diesel engines as it has the potential of achieving a more homogeneous and leaner mixture close to TDC compared to conventional diesel engines. Because this concept reduced NOx and smoke emissions simultaneously. Early studies are shown that in a HCCI(Homogeneous Charge Compression Ignition) engine, the fuel injection timing and intake air temperature affect the mixture formation. The purpose of this study is to investigate characteristics of combustion and mixture formation according to injection timing and intake air temperature in a common rail direct injection type HCCI engine using an early injection method called the PCCI(Premixed Charge Compression Ignition). From this study, we found that the fuel injection timing and intake air temperature affect the mixture formation and in turn affects combustion in the PCCI engine.

• 한국축산식품학회지
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• 제22권4호
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• pp.363-372
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• 2002

Reducing the fat content of processed meat products can be performed by (1) using leaner raw meat materials (2) inducing non-meat ingredients that serve to replace a portion or all of the fat, and (3) applying new ingredient combinations, technologies or processing procedures that decrease the fat and cholesterol content of meat products. Low-fat meat products were manufactured with Int replacers which were food ingredients that had the functional and sensory properties of fat without contributing fat calories, resulting in lower fat(<3%) content. Added water, non-meat proteins, carbohydrates, such as starch and hydrocolloids(gums) and vegetable oils have been used as typical fat replacers to be used in meat products. In addition, fat substitutes included structural lipids, sucrose polyester and ingredient combinations. Formulations for the manufacture of low-fat meat products in combined with new technologies have focused on the use of fat replacer combinations that contributes a minimum of calories and not detrimental to flavor, juiciness, mouthfeel or textural traits expected more traditional products. In conclusion, some combinations of fat replacements that mimics the flavor, mouthfeel and textural characteristics of fat offer potential for further development of low-fat meat products to have similar characteristics of regular-fat counterparts.