• Tribology and Lubricants
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• 제10권1호
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• pp.14-26
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• 1994

The minimum oil film thickness(MOFT) in the connecting-rod bearing of a 1.5 liter, L-4, gasoline engine is measured up to 5500 rpm and calculated to study the dynamically loaded engine bearing. Short bearing approximation and Mobility method are used for theoretical analysis of oil film characteristics. And cylinder pressure, crank-pin surface temperature and bearing temperature are measured as the input data of theoretical analysis. The MOFT are measured by the total capacitance method(TCM). To improve the reliability of the test results, a reasonable determination method of bearing clearance is introduced and used, and the effects of cavitation and aeration on the test results are neglected. The crankshaft is grounded by means of a slip ring. A scissor type linkage system was developed to measure the MOFT and bearing temperature. The effects of engine speed, load and oil viscosity on the measured and calculated minimum oil film thicknesses are investigated at 1500 to 5500 rpm. From the comparison between the measured and calculated MOFT, it is found that a qualitative similarity exists between them, but in all cases, the measured MOFT are smaller than those calculated.

• 한국컴퓨터정보학회논문지
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• 제20권1호
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• pp.207-216
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• 2015

IT 기술의 발달은 컴퓨터를 이용하여 상호간에 정보를 주고 받으며 작전을 지휘하는 등 군 작전에 있어서 많은 변화를 가져왔다. 특히 해군의 경우 암호화된 유 무선망을 통해 실시간으로 이루어지는 문자 교신을 작전 훈련에 활용하고 있다. 하지만 이는 단순한 정보 교환에만 이용되고 있으며 실제 작전 훈련에 필요한 정보(교범, 지침서 등)의 내용은 필요할 때마다 찾아보고 있는 실정이다. 이에 따라 본 논문에서는 ECA 규칙을 문자 교신과 연동시켜 실시간으로 필요한 정보를 제공할 수 있는 규칙 기반 엔진을 설계하였으며 가상 시나리오 적용을 통해 이를 검증한 결과 83%의 정확율을 보였다.

• Tribology and Lubricants
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• 제32권4호
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• pp.132-139
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• 2016

The piston of a marine diesel engine works under severe conditions, including a combustion pressure of over 180 bar, high thermal load, and high speed. Therefore, the analyses of the fatigue strength, thermal load, clamping (bolting) system and lubrication performance are important in achieving a robust piston design. Designing the surface profile and the skirt ovality carefully is important to prevent severe wear and reduce frictional loss for engine efficiency. This study performs flexible multi-body dynamic and elasto-hydrodynamic (EHD) analyses using AVL/EXCITE/PU are performed to evaluate tribological characteristics. The numerical techniques employed to perform the EHD analysis are as follows: (1) averaged Reynolds equation considering the surface roughness; (2) Greenwood_Tripp model considering the solid_to_solid contact using the statistical values of the summit roughness; and (3) flow factor considering the surface topology. This study also compares two cases of skirt shapes with minimum oil film thickness, peak oil film pressure, asperity contact pressure, wear rate using the Archard model and friction power loss (i.e., frictional loss mean effective pressure (FMEP)). Accordingly, the study compares the calculated wear pattern with the field test result of the piston operating for 12,000h to verify the quantitative integrity of the numerical analysis. The results show that the selected profile and the piston skirt ovality reduce friction power loss and peak oil film pressure by 7% and 57%, respectively. They also increase the minimum oil film thickness by 34%.

• 항공우주시스템공학회지
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• 제14권3호
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• pp.60-68
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• 2020

항공기 엔진 내의 파손된 블레이드가 케이스를 관통하여 외부로 나가게 되면, 동체에 부딪혀 승객의 안전을 위협하게 된다. 따라서 엔진 케이스 설계 시 항공청의 안전성 평가 인증을 받아야한다. 본 논문에서는 국내의 독자적인 엔진 개발을 위해 필요한 엔진 케이스의 컨테인먼트 인증 요구조건과 개발 기술에 대하여 조사하였다. 미국과 유럽의 항공청에서 제시하는 컨테인먼트 안전성 요구 조건을 정리하고 이 인증에 부합하는 케이스의 파편 봉쇄를 검증하는 실험적/해석적 방법에 대하여 확인하였다. 컨테인먼트 케이스에 대한 최근의 연구를 분석하여 케이스 개발 시 검증 방법을 제시하고자 한다.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2010년도 춘계학술발표대회
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• pp.852-855
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• 2010

트리 유형의 규칙들을 처리하는 기존의 규칙기반시스템은 실제의 규칙들을 절차형 프로그램으로 구성된 규칙 엔진에게 제공하여 결과값을 반환받는 형식으로 동작한다. 이와 같은 방식은 두 가지 단점이 있는데, 그 하나는 업무의 변경에 따라 규칙 엔진을 변경해야 한다는 점이고, 또 하나는 엄청나게 많은 규칙들을 가진 경우에는 규칙 엔진이 복잡해지고 규칙 엔진의 속도가 저하된다는 점이다. 본 연구에서는 ID 트리의 원리를 적용하여 규칙기반시스템에 사용되는 규칙들을 생성하는 규칙간소화 알고리듬을 제안한다. 제안하는 알고리듬은 규칙기반시스템에 필요한 최소의 규칙들을 생성할 수 있을 뿐 아니라 업무가 변경되는 경우 알고리듬의 수행으로 쉽게 규칙들을 생성할 수 있으므로 업무변화에 유연하다. 그리고 규칙 엔진이 필요하지 않아 수행속도의 향상과 경비 절감의 효과도 기대한다.

• 동력기계공학회지
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• 제8권2호
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• pp.5-11
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• 2004

The failure frequency of the Emergency Diesel Generator(EDG) at Nuclear Power Plants(NPPs) is not so much lower than that of the Marine engines, whereas the running hours of the diesel engine at NPPs is much less than those of the engines for commercial service. The primary factor results from the severe surveillance test requirements such as fast start, large number of starting test, fast load-run, high load running, etc. The other factor comes from the excessive maintenance based on the engine maker's instruction manual that did not incorporate the peculiar characteristics of the diesel engines at NPPs. In this paper, the present preventive maintenance program on the basis of the Pielstick diesel engines was reviewed for the purpose of securing the reliability of the emergency diesel generator at NPPs and the ways for its improvement were presented by referring to the overseas cases for their applications.

• 한국자동차공학회논문집
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• 제20권3호
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• pp.45-51
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• 2012

This work was investigated 2-stage injection strategy on combustion and emissions in a direct injection compression-ignition engine fueled with DME. Single cylinder engine was equipped with common rail. Injection pressure was 700bar, dSOI between the main injection and the pilot injection was varied. Diesel was used as compared fuel of DME in all cases. The results was shown that maximum pressure was higher than all cases and its amount of DME and diesel was similar. Regardless the pilot injection, the main fuel injection timing was same. The heat release rate of the main injection for diesel was high while that of pilot injection for DME was high. The THC was very low regardless of the fuel type and injection strategy. In the single injection, NOx was increased to retard of main injection timing regardless of the fuel type. NOx emissions was decreased with the retardation of the main injection timing regardless of the fuel type in the case of 2-stage injection strategy.

• 한국자동차공학회논문집
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• 제14권4호
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• pp.26-31
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• 2006

An experimental investigation of an early injection strategy was conducted on a small single cylinder common-rail DI diesel engine to reduce the oxides of nitrogen($NO_x$) emission. The main objectives of this study were to investigate the emissions, performance and combustion characteristics in a diesel engine with early and two-stage injections. The two- stage injection was conducted to reduce the wall-wetting of early injected fuels on the cylinder wall or to promote the ignition of premixed charge. The engine test was performed at conditions of 1500rpm, injection timing ranging from TDC to BTDC $80^{\circ}$. The experimental results show that $NO_x$ emissions were decreased in both cases of early injection and two stage injection compared to the conventional diesel combustion by the near TDC injection. However, soot and products of incomplete products (i.e. HC and CO) are slightly increased. Also, the second injection near TDC promoted the ignition of premixed fuel, therefore, IMEP was increased.

• International Journal of Automotive Technology
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• 제8권4호
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• pp.421-428
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• 2007

This paper investigates the combustion and emission characteristics of a compression ignition engine fueled with neat and blended Shell's gas-to-liquid (GTL) fuel, which was derived from natural gas through the Fischer-Tropsch process. The experiments were conducted in a 6-cylinder DI diesel engine with pump timing settings of $6^{\circ},\;9^{\circ}\;and\;12^{\circ}$crank angle before TDC over ECE R49 and US 13-mode cycles separately and compared to a conventional diesel fuel. The results show that GTL exhibited almost the same power and torque output, improved fuel economy and effective thermal efficiency. It was found that GTL displayed lower peak in-cylinder combustion pressure and maximum heat release rate (HRR), the timings of the peak pressure and the maximum HRR were generally delayed, and the combustion durations were almost equivalent for diesel and GTL under the same speed-load condition. The results also indicate that, compared to diesel fuel, GTL blends showed a trend forward decreasing four regulated emissions simultaneously and a higher GTL fraction in blends contributing to further reductions in the emissions. In particular and on average, neat GTL significantly reduced HC, CO, NOx and PM by 16.4%, 17.8%, 18.3% and 32.4%, respectively, for all cases.

• 한국전산유체공학회지
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• 제22권1호
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• pp.43-50
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• 2017

Thermal flowfield of a micro turbojet engine was computationally investigated for exhaust nozzles with different aspect ratio and curvature. Special attention was paid to maximum and average temperature of the nozzle surface and the exhaust nozzle plume. The IR signatures of the micro turbojet engine nozzle were then calculated through the narrow-band model based on thermal flowfield data obtained through CFD analysis. Finally, in order to check the similarity of thermal flowfields and IR signature of the sub-scale micro turbojet engine model and the full-scale UCAV propulsion system, several non-dimensional parameters associated with temperature and optical property of plume were introduced. It was shown that, in spite of some differences in actual values of non-dimensional parameters, the scaling characteristics on spectral feature of IR signature and effects of aspect ratio and curvature of nozzle configuration remain similar in sub-scale and full-scale cases.