• Tribology and Lubricants
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• 제13권3호
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• pp.63-72
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• 1997

The stability of a rotor-bearing system supported by swirl-controlled hybrid journal bearing with pair-type angled injection orifices is investigated for improvement of the whirl frequency ratio by allowing effective control of the tangential flow inside the bearing clearance, i.e., by achieving more freedom in controlling strength and direction of the supply tangential flow inside the bearing clearance. It is suggested that the system instability can be improved through the change of bearing dynamic characteristic parameters with the swirl control. The orifice diameter $d_0$ and recess injection angle $\alpha$ along with combinations of swirl/anti-swirl supply pressures and directions (3.0~3.0 MPa, 4.0~2.0 MPa, 2.0~4.0 MPa) are selected for design parameters for swirl-controlled effective factors dependent on journal speeds (3000, 9000, 15000, 21000 rpm). It has been found that the orifice diameter $d_0$ shows strong effects on effective maneuverability of direct-stiffness and direct damping values, while recess injection angle $\alpha$ results in substantial effects on the magnitude and direction of cross-stiffness. Specifically, recess injection parameters which are functions of angle of orifice feeding flow and recess dimensions showed very feasible effect on the stability control of swirl-controlled rotor-bearing system.

• Journal of Advanced Marine Engineering and Technology
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• 제24권2호
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• pp.38-49
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• 2000

A diesel engine has been studied for many years to improve fuel economy and to reduce emissions as important factors governing the emission performance of diesel engines. This study addresses to swirl effects on combustion characteristics in a large diesel engine. The transport equations of flows and chemical reactions are given for fully compressible fluid. The simulations have been done for compression and expansion strokes and the results are given at several crank angles which are the angles at just before injection start, TDC, ATDC 90 and just before exhaust valve open. The results show that the strength of the swirl flow makes many effects on burning fuel and forming emissions.

• 한국자동차공학회논문집
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• 제18권6호
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• pp.145-151
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• 2010

The performance of a direct-injection diesel engine often depends on the strength of swirl or squish, the shape of combustion chamber, the number of nozzle holes, etc. This is natural because the combustion in the cylinder was affected by the mixture formation process. Since the available duration to make the mixture formation of air-fuel is very short, it is difficult to make complete mixture. Therefore, an early stage of combustion is violent, which leads to the weakness of noise and vibration. In this paper, the combustion process of a common-rail diesel engine was studied by employing two kinds of pistons. One has several grooves with inclined plane on the piston crown to generate swirl during the compression and expansion strokes in the cylinder in order to improve the atomization of fuel. The other is a toroidal piston, generally used in high speed diesel engines. To take photographs of flame and flaming duration, a four-stroke diesel engine was remodeled into a two-stroke visible single cylinder engine and a high speed video camera was used.

• 한국자동차공학회논문집
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• 제17권1호
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• pp.105-113
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• 2009

The performance of a direct-injection type diesel engine often depends on the strength of swirl or squish, shape of combustion chamber, the number of nozzle holes, etc. This is of course because the combustion in the cylinder was affected by the mixture formation process. In this paper, combustion process of biodiesel fuel was studied by employing the piston which has several grooves with inclined plane on the piston crown to generate swirl during the compression stroke in the cylinder in order to improve the atomization of high viscosity fuel such as biodiesel fuel and toroidal type piston generally used in high speed diesel engine. To take a photograph of flame, single cylinder, four stroke diesel engine was remodeled into two stroke visible engine and high speed video camera was used. The results obtained are summarized as follows; (1) In the case of toroidal piston, when biodiesel fuel was supplied to plunger type injection system which has very low injection pressure as compared with common-rail injection system, the flame propagation speed was slowed and the maximum combustion pressure became lower. These phenomena became further aggravated as the fuel viscosity gets higher. (2) In the case of swirl groove piston, early stage of combustion such as rapid ignition timing and flame propagation was activated by intensifying the air flow in the cylinder. (3) Combustion process of biodiesel fuel was improved by the reason mentioned in paragraph (2) above. Consequently, the swirl grooves would also function to improve the combustion of high viscosity fuel.

• 한국항공우주학회지
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• 제49권2호
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• pp.139-146
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• 2021

하이브리드 로켓 연소에서 산화제 스월 분사는 회전방향 속도성분이 경계층 유동에 영향을 미쳐 연소안정화에 기여한다. 그러나 스월 강도가 증가할수록 연소성능을 과도하게 변화시키는 문제점이 나타난다. 따라서 참고문헌[7]의 삽입연료와 함께 사용하여 연소성능 변화를 최소화 하면서 연소불안정 억제를 시도하였다. 이를 위해, 일련의 실험을 계획하여 스월 강도와 삽입연료 위치를 변화하며 연소불안정의 발생과 연소성능 변화를 관찰하였다. 실험결과, 스월 각 6°, 삽입연료 위치 310 mm 조합에서 연소불안정이 억제되었으며 연소압력, O/F 비 그리고 연료 후퇴율 등의 변화가 최소인 것으로 확인하였다. 또한 고주파수 대역의 압력진동(p')와 열방출진동(q')의 위상차가 π/2로 음의 결합을 형성하도록 연소조건을 유지하는 것이 저주파수 연소불안정 발생을 억제하는 필요충분조건임을 재확인하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.3038-3043
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• 2008

Tumble or swirl flow is used adequately to promote mixing of air and fuel in the cylinder and to enlarge turbulent intensity in the late time of compression stroke. However, since in-cylinder flow is a kind of transient state with rapid flow variation, that is, non-steady state flow, swirl or tumble flow has not been analyzed sufficiently and not been recognized whether they are available for combustion theoretically yet. In the investigation of intake turbulent characteristics using PIV method, different flow characteristics were showed according to SCV figures. SCV installed engine had higher vorticity, turbulent strength by fluctuation and turbulent kinetic energy than a baseline engine, especially around the wall and lower part of the cylinder. Consequently, as swirl flow was added to existing tumble flow, it was found that fluctuation component increased and flow energy was conserved effectively through the experiment.

• 대한환경공학회지
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• 제36권12호
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• pp.837-842
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• 2014

LNG 난류 화염에서 수증기나 물을 전기분해한 기체를 투입할 경우 발생하는 NO 생성을 예측하기 위하여 컴퓨터 프로그램을 개발하였다. 본 연구는 그 첫 번째로서 NO 생성에 대한 수증기 영향을 다룬 연구이다. 개발한 이 프로그램을 한국에너지기술연구원에서 실험 연소로를 대상으로 적용하였다. 수증기 양에 따른 LNG 화염에서 NO 생성 효과를 검토하기 위하여 투입된 전체 공기량에 수분양을 0~10%까지 2% 간격으로 주입하였다. 계산 결과 강한 선회 유동의 결과로 나타나는 전형적인 유동분리에 따른 화염분리와 함께 NO 농도가 분리되는 양상이 나타났다. 수분양이 증가하면서 출구에서의 연소가스의 온도와 NO의 농도는 $973^{\circ}C$에서 $852^{\circ}C$로 NO의 농도는 139 ppm에서 71 ppm으로 일관성 있게 감소하였다. 그리고 연소로 복사 현상은 본 연구에서 고려한 영역에서 선회강도보다도 NO 생성에 큰 영향을 나타내었다. 그러나 본 연구에서 고려한 강한 선회 효과는 NO 농도가 연소로 전단에 이어 출구 근처에서 다시 높아지는 분리 현상을 나타내었다.

• Journal of Advanced Marine Engineering and Technology
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• 제28권3호
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• pp.475-481
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• 2004

Recently it is strongly required on lower fuel consumption. lower exhaust emission, higher engine performance. and social demands in a spark ignition gasoline engine. In this study. the experimental engine used at test. it has been modified the lean burn gasoline engine. and used the programmable engine management system, and connected the controller circuit which is designed for the engine control. At the parametric study of the engine experiment, it has been controlled with fuel injection, ignition timing. swirl mode, equivalence ratio engine dynamometer load and speed as the important factors governing the engine performance adaptively. It has been found the combustion characteristics to overcome the hysteresis phenomena between normal and lean air-fuel mixing ranges. by mean of the look-up table set up the mapping values. at the optimum conditions during the engine operation. As the result, it is found that the strength of the swirl flow with the variation of engine speed and load is effective on combustion characteristics to reduce the bandwidth of the hysteresis regions. The results show that mass fraction burned and heat release rate pattern with crank angle are reduced much rather, and brake specific fuel consumption is also reduced simultaneously.

• 한국군사과학기술학회지
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• 제22권6호
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• pp.763-772
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• 2019

There is a need to use sheath flow nozzle to detect bioaerosol such as virus and bacteria due to their characteristics. In order to enhance the detection performance depending on nozzle parameters, numerical analysis was carried out using a commercial code, ANSYS CFX. Eulerian-lagrangian approach method is used in this simulation. Multiphase flow characteristics between primary fluid and solid were considered. The detection performance was evaluated based on the results of flow field in nozzle chamber such as focusing efficiency and swirl strength. In addition, Latin hypercube sampling(LHS) of design of experiment(DOE) was used for generating a near-random sampling. Then, the acceleration section is optimized using response surface method(RSM). Results show that the optimized model achieved a 6.13 % in a focusing efficiency and 11.47 % increase in swirl strength over the reference model.

• 한국추진공학회지
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• 제20권4호
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• pp.68-76
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• 2016

본 연구는 이원추진제 추력기의 핵심부품에 대한 성능평가의 일환으로, 기체메탄/액체산소를 추진제로 사용하는 스월 동축형 인젝터의 리세스 길이 및 분사압력에 따른 분무특성 파악을 목표로 하였다. 분무형상은 슐리렌 가시화 기법을 이용하여 획득하였고, 슐리렌장치는 광원, 오목거울, 초고속카메라 등으로 구성된다. 내부 인젝터에 의한 액체 분무의 경우 hollow cone 형상을 확인하였으며, 내부 인젝터 오리피스 길이의 증가와 함께 스월강도 감쇠의 영향으로 분무각은 줄어들었다. 기체-액체를 함께 분사할 때, 분무각은 리세스 길이가 증가함에 따라 외부혼합영역에서 증가하지만, 내부혼합영역에서는 작아졌는데, 액체분무 분사 압력의 높고 낮음에 무관하다는 사실을 확인하였다.