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플립러닝 교수법에서 사전학습태도가 학업성취도에 미치는 영향 (응용열역학 교과목 적용 사례)
유경현 한국공학교육학회 2023 공학교육연구 Vol.26 No.6
In this study, the effects of pre-learning attitude on learning participation and academic achievement was analyzed when applying the flipped learning methodology to engineering subject education. The modified PARTN teaching and learning model was applied, and pre-class survey, assessment on learning in pre-class, and post-class survey were conducted to analyze the effectiveness of flipped learning. The results were analyzed for 24 students who took the applied thermodynamics lecture. They were asked to take the course with the videos provided in the pre-class stage, and a pre-learning assessment was conducted to measure the completeness and understanding of the learning. As a result of the study, it was found that students with relatively excellent learning ability had excellent pre-learning evaluation results and excellent final academic achievement. In addition, the lower the pre-learning completion rate within the pre-learning period or the higher the learning rate using mobile devices, the more difficult it was to faithfully complete pre-learning, leading to poor pre-learning evaluation results. Meanwhile, the survey revealed that conducting pre-learning assessments were helpful in encouraging individual learning. In addition, cases reflecting pre-learning evaluation results to course grades showed higher pre-learning evaluation results than cases not reflecting pre-learning evaluation results to course grades, and in flipped learning classes, pre-learning evaluations act as a factor that promotes pre-class learning.
유경현 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.11
Biodiesel fuels that consist of saturated and unsaturated long-chain fatty acid alkyl esters are an alternative diesel fuel produced from vegetable oils or animal fats. However, autoxidation of biodiesel fuels during storage is easily caused by air, reducing fuel quality by adversely affecting its properties such as kinematic viscosity and acid value. One approach to improve the resistance of biodiesel fuels to autoxidation is to mix them with antioxidants. This study investigated the effectiveness of five such antioxidants in mixtures with biodiesel fuels produced by three biodiesel manufacturers: butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), tert-butylhydroquinone (TBHQ), propyl gallate (PrG) and α-tocopherol. An engine test was also performed to investigate the combustion characteristics of biodiesel fuel with antioxidants in an indirect-injection (IDI) diesel engine. Oxidation stability was determined using Rancimat equipment. The results showed that TBHQ, BHA, and BHT were the most effective and α-tocopherol was the least effective in increasing the oxidation stability of biodiesel. The combustion characteristics and exhaust emissions in diesel engine were not influenced by the addition of antioxidants in biodiesel fuel. This study recommends TBHQ and PrG to be used for safeguarding biodiesel fuel from the effects of autoxidation during storage.
유경현,오영택,Ryu, Kyung-Hyun,Oh, Young-Taig 한국자동차공학회 2007 한국 자동차공학회논문집 Vol.15 No.3
Three diesel engines were fueled with BDF 20, a blend of 80% diesel fuel and 20% biodiesel fuel by volume, and run in excess of 200 h to evaluate their combustion characteristics and durability. The engines used for this study were a 4-cylinder 2476-cc displacement IDI diesel engine(Engine 1), a 4-cylinder l732-cc displacement IDI diesel engine(Engine 2), and a single cylinder 673-cc displacement DI diesel engine(Engine 3). Engine dynamometer testing was performed on each engine at regularly scheduled intervals to monitor the performance and exhaust emissions, which were sampled at 1h intervals for analysis, The peak combustion pressure with BDF 20 increased in Engines 1 and 3 over that measured when burning pure diesel fuel, but that in Engine 2 remained constant. Combustion parameters, such as the maximum combustion pressure and corresponding crank angle, did not change over the long-term dynamometer testing. The BSFC with BDF 20 in Engine 1 was less than that measured with pure diesel fuel. The amount of smoke produced with BDF 20 was less for all engines ; the greatest reduction was observed for Engine 3. The NOx emissions were lower in the IDI engines than the DI engine. The traditional trade-off between smoke and NOx emissions was maintained for BDF 20 fuel for Engines 1 and 3. There was not a big difference in the $CO_2\;and\;O_2$ emissions for BDF 20, as compared to pure diesel fuel, but more $CO_2$ was exhausted by Engine 1 than by Engines 2 or 3 and less $O_2$ was exhausted by Engine 1 than by Engines 2 or 3. The engine parts remained clean, except for some carbon attached to the area surrounding the nozzle hole of the DI diesel engine.
흡기관내로의 물 분사에 의한 디젤기관의 연소특성 (I)
유경현,윤용진,오영택,Ryu, Kyung-Hyun,Yun, Yoong-Jin,Oh, Young-Taig 대한기계학회 2002 大韓機械學會論文集B Vol.26 No.12
To effectively meet current regulations on the exhaust emissions of diesel engine required to control the deterioration of air pollution in the whole world, this study is to investigate the effects of water induction through the air intake system on the characteristics of combustion and exhaust emissions in IDI diesel engine. A method fur supplying water through the air intake system to reduce the exhaust emissions has been considered with other methods such as water introduction in the form of water-in-fuel emulsion or water injection directly into the combustion chamber, but it has not been studied about the effects of water on the combustion concepts and the characteristics of exhaust emissions in detail until now. In this study, the formation of NOx was significantly suppressed by decreasing the gas peak temperature during the initial combustion process because the water play a role as a heat sink during evaporating in the combustion chamber, but the smoke was slightly increased by increasing water amount.
바이오디젤유(미강유 에스테르)를 이용한 농업용 디젤기관의 연소 특성
유경현,윤용진,오영택,Ryu, Kyung-Hyun,Yun, Yoong-Jin,Oh, Young-Taig 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.2
Biodiesel fuel as an alternative fuel for diesel engine has a great possibility to solve the problems such as air pollution. It is a domestically produced, renewable fuel that can be manufactured from vegetable oils, used vegetable oils, or animal fats. In this study, the usability of biodiesel fuel derived from rice bran oil as an alternative fuel for diesel engines was investigated in agricultural diesel engine. Emissions were characterized with neat biodiesel fuel and with a blend of biodiesel fuel and conventional diesel fuel. Since the biodiesel fuel includes oxygen of about 11%, it could influence the combustion process strongly. So, the use of biodiesel fuel resulted in lower emissions of carbon monoxide, carbon dioxide, and smoke emissions without any increase of oxides of nitrogen. It is concluded that biodiesel fuel can be utilized effectively as a renewable and an environmentally Innocuous fuel for diesel engine.