바이오디젤-CNG 혼소 엔진시스템에서 압축비가 성능 및 연소 특성에 미치는 영향

유경현,원종근 한국자동차공학회 2024 한국 자동차공학회논문집 Vol.32 No.2

This paper explores the effects of compression ratio on the performance and emission characteristics of abiodiesel-CNG dual-fuel combustion system in a single-cylinder direct injection diesel engine. Engine tests were conducted with the compression ratios(CR) of 14.5 and 16.5 at an engine speed of 1,700 rpm and various engine loads. This study showed that the cylinder pressure peak of the dual-fuel combustion decreased as CR decreased. The ignition delay periods of the pilot fuel at CR 14.5 increased compared to those at CR 16.5. For maximum output, the pilot injection timing of CR 14.5 should be advanced approximately by 5 % compared to CR 16.5. Engine operation became stable with a COVimep of 3 % at CR 14.5, except when there is no load. The biodiesel-CNG dual-fuel combustion system reduced smoke emissions compared to a conventional single-fuel diesel combustion system. As CR decreased, smoke emission also decreased.

6-sigma 방법론을 적용한 종합설계 교육모델 개발

유경현 한국공학교육학회 2020 공학교육연구 Vol.23 No.4

Capstone design education is essential in the engineering design process according to the certification standards of ABEEK. Capstone design process should be properly trained in undergraduate courses in order to increase the design ability of systems, components and processes within realistic constraints. In this study, a modified design model as a capstone design education model was proposed to reduce the separation between the design process at industrial sites and the design process at university education. The modified design model based on 6-sigma methodology is composed of 6 design steps such as define, measure, analyse, design, verify, and report. Each step has appropriated design contents and tools, and is configured to generate design results. The proposed design model was directly applied to the capstone design class for automotive engineering in Kunsan National University, and it was confirmed that the proposed DMADVR methodology was a very useful design education model to enhance the design ability, teamwork ability and communication skills required by ABEEK.

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.

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.

Fe 이온 치환 beta-tricalcium phosphate의 하소 온도에 따른 미세구조 및 분해 특성

유경현,김현진,선우경,윤석영 한국결정성장학회 2020 한국결정성장학회지 Vol.30 No.6

β-삼인산칼슘(β-tricalcium phosphate, β-TCP, Ca3(PO4)2)은 뼈와 유사한 성분을 가지는 인산 칼슘계 세라믹 중 하나로, 생분해성과 골 전도성을 가지고 있어 골 대체재 등으로 다양하게 사용된다. 이러한 β-TCP의 생체 활성과 골유도성을향상시키기 위해 다양한 이온 치환 연구가 진행되어왔으며 그 중 철 이온은 필수 미량 원소로 체내에서 다양한 기능을 한다. 본 연구에서는 β-TCP에 철 이온이 치환되었을 때 열처리 온도에 따른 구조의 변화를 분석하고, 이에 따른 생분해 특성을 평가하였다. 또한 분해 후의 구조를 분석하여 분해 거동을 확인하였다. 철 이온을 치환한 β-TCP는 공침법으로 합성을하였고, 925℃와 1100℃에서 하소 처리를 실시하였다. X-선 회절 분석과 Rietveld refinement를 이용하여 구조 분석을 실시하였다. 철 이온은 온도에 따라 Fe2+또는 Fe3+ 상태로 바뀌기 때문에 β-TCP에 치환되었을 때 열처리 온도에 따라 치환 위치(Ca(4), Ca(5))가 바뀌고, 1100℃에서 열처리를 실시한 철 이온 치환 β-TCP의 분해 속도가 가장 빨랐다. 또한 세포 증식특성이 향상된 것을 통해 β-TCP에 철 이온을 치환하는 것이 생체적합성과 생체 활성 특성을 향상시키고 골 결손부 회복등 더욱 다양한 분야에 사용될 수 있을 것으로 기대된다. β-Tricalcium phosphate (β-TCP, Ca3(PO4)2) is a kind of biodegradable calcium phosphate ceramics with chemicaland mineral compositions similar to those of bone. It is a potential candidate for bone repair surgery. To improve thebioactivity and osteoinductivity of β-TCP, various ions doped calcium phosphate have been studied. Among them, Iron is atrace element and its deficiency in the human body causes various problems. In this study, we investigated the effect of Feions on the structural variation, degradation behavior of β-TCP. Fe-doped β-TCP powders were synthesized by the coprecipitationmethod, and the heat treatment temperature was set at 925 and 1100℃. The structural analysis was carried out by Rietveld refinement using the X-ray diffraction results. Fe ions existed in a different state (Fe2+ or Fe3+) with different heat treatment temperatures, and the substitution sites (Ca-(4) and Ca-(5)) also changed with temperature. The degradation rate was fastest at Fe-doped β-TCP with heated at 1100℃. The cell viability behavior was also enhanced with the substitution of Fe ions. Therefore, the substitution of Fe ion has accelerated the degradation of β-TCP and improved the biocompatibility. It could be more utilized in biomedical devices.

Papaverine이 단일 심근세포의 막전류에 미치는 영향

유경현,심태섭,방효원 중앙대학교 의과대학 의과학연구소 1991 中央醫大誌 Vol.16 No.4

Ventricular myocytes of guinea-pig were isolated by means of collagenase digestion in order to investigate the effects of papaverine on the membrane currents in them. After formation of a gigaseal with patch microelectrodes, membrane currents were recorded from single ventricular myocytes in a whole cell mode of patch-clamp technique. For membrane currents recording, electrodes were filled with Cs-solution. Results were as follows: 1. Slow inward calcium was reduced by papaverine dose-dependently. 2. No significant changes were observed in the steady-state inactivation. 3. Recovery time of the calcium currents prolonged in high concencial papaverine. 4. Fast inward sodium currents showed no noticeable changes with papaverine treatment. From these results, it is strongly suggested that the effects of papaverine on the membrane currents in the single ventricular myocytes may be attributable to its antagonistic action on the calcium channel rather than its inhibitory effect on the phosphodiesterase activity.

2008 Student Formula SAE competition of JAPAN

유경현,김덕중 한국자동차공학회 2008 한국자동차공학회 지부 학술대회 논문집 Vol.2008 No.11

Multiple TCM 코드에서의 Uniform TCM 조건의 적용 ( Application of Uniform TCM Conditions to Multiple TCM Scheme )

유경현,김기호 한국통신학회 1995 한국통신학회 학술대회논문집 Vol.- No.-

Effect of antioxidants on the oxidative stability and combustion characteristics of biodiesel fuels in an indirect-injection (IDI) diesel engine

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.

초고속 가입자선 전송의 기술동향 ( Very high-speed Digital Subscriber Lines ( VDSL ) )

유경현 한국통신학회 1998 한국통신학회 학술대회논문집 Vol.- No.-