• Journal of ILASS-Korea
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• v.22 no.3
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• pp.129-136
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• 2017

Effects of collision angle on heat transfer characteristics of a liquid droplet impinging on a heated wall above the Leidenfrost point temperature were experimentally investigated. The heated wall and droplet temperatures were $506^{\circ}C$ and $100^{\circ}C$, respectively, and the impact angle varied from $20^{\circ}$ to $90^{\circ}$ while the normal collision velocity was constant at 0.27 m/s. The droplet collision behaviors and the surface temperature distribution were measured using synchronized high-speed video and infrared cameras. The major physical parameters influencing upon droplet-wall collision heat transfer, such as residence time, wall heat flux, effective heat transfer area, heat transfer amount, were analyzed. It was found at the constant normal collision velocity that the residence time, wall heat flux and effective heat transfer area were hardly not changed, resulting in the almost constant heat transfer amount.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.04a
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• pp.2-2
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• 1999

액체추진제 로켓엔진에서 분사기의 미립화 및 혼합 특성과 그에 따른 연소 특성은 성능과 안정성을 결정하는 중요한 파라미터이며 분사기는 제한된 설계 조건하에서 최대의 열방출율을 발휘하도록 설계되어야 한다. 여기서 연소효율은 연료와 산화제의 혼합특성과 충돌 분무의 미립화의 정도에 의해 결정되므로 충돌 분무 유동성의 혼합, 미립화 특성과 이에 따른 인조성능 특성을 명확하게 밝힘으로써 최대 엔진성능을 위한 설계가 가능하게 된다. 분사기의 설계에는 분사요소형태, 분사공의 형상 및 유동시스템 등이 포함되며 특히 분사요소 형태의 선택에는 추진제, 연소실냉각방법, 연소실 형상, 자동조건 및 엔진의 수명 등이 중요한 제한조건으로 고려된다. 이런 형태의 분사 요소들 중, 충돌형 분사기는 저장성 추진제를 사용하는 중, 저추력의 액체추진제 로켓엔진에 주로 사용된다. 이 분사형태는 미립화 성능이 높지 않고, 분사공 직경 및 운동량비에 따른 혼합성능이 만감하며 blow apart 등에 의한 열부하 혹은 안정성에 대한 문제가 있으나 양호한 혼합효율, 신뢰성과 제작의 용이함으로 인하여 광범위하게 사용된다.

• Journal of ILASS-Korea
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• v.2 no.2
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• pp.8-15
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• 1997

Combustion chamber systems using spray impinged on walls have been studied for improving combustion characteristics in high speed direct injection diesel engines. The fuel spray injected in a small combustion chamber may be easily impinged and deposited on the wall. The fuel deposit has been considered as the cause for unburned emission due to difficulty of fuel-air mixing. In this paper w-shaped combustion chamber which has four raised pips on the side wall is introduced and discussed by comparing with conventional chamber with no pips. The computer code employing new spray-wall interaction model in general non-orthogonal grids is used in here. The model is applied into the new chamber shape with raised pips. In this chamber system four-hole nozzle is used, and the sprays injected from the each hole impact on lands raised from the chamber wall surface. After impacting, the sprays break up into much smaller drops and distribute over all the chamber space, instead of distributing just near the wall surface in conventional omega-shape. The results showed the potential of the w-shaped chamber employing pips for dispersing droplets so as tn avoid the fuel deposit regions.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.4
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• pp.44-54
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• 2018

In a spray experiment using a venturi mounted on a lean premixed LPP injector, droplets appear to have non-uniform distributions. To solve this problem, the exit angle of the venturi was changed to form a dump surface on the nozzle neck. The dump surface improved the atomization performance and minimized droplet loss while forming recirculation zone in the venturi exit. In order to solve the non-uniform spray of the injector, the flow characteristics inside the venturi and SMD of the spray are compared. Finally, an optimum venturi shape is selected to minimize the spray loss and improve the spray performance.

• Journal of computational fluids engineering
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• v.13 no.2
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• pp.68-72
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• 2008

NUFLEX is a general purpose thermo/fluid flow analysis program which has various physical models including spray. In NUFLEX, spray models are composed of breakup and collision models of droplet. However, in case of diesel engine, interaction between wall-film and impingement model considering heat transfer is not coded in NUFLEX. In this study, Lee & Ryou impingement & wall-film model considering heat transfer is applied to NUFLEX. For the verification of this NUFLEX program, numerical results are compared with experimental data. Differences of film thickness and radius between numerical results and experimental data are within 10% error range. The results show that NUFLEX can be used for comprehensive analysis of spray phenomena.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.5
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• pp.30-37
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• 2001

Most gasoline engines employ a port injection system to achieve the better fuel-air mixing. A part of injected fuels adheres to the wall or intake valve and forms a film of liquid fuel. The other is secondarily atomized by the spray-wall interaction. A better understanding of this interaction will help in designing injection systems and controlling the strategies to improve engine performance and exhaust emissions. In the present research, the spray-wall interaction was investigated by a laser sheet visualization method. The shape of sprays was pictured at various impinging velocities and angles. The fuel dispersion was estimated by fluorescence light, and the atomization was evaluated by the enlarged images of droplets. The experimental results were compared with model predictions which are based on OPT method. The model has been modified to have the better agreement with the experimental result, and was implemented in the KIVA-II code.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.3
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• pp.77-84
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• 2003

It is an aim of this study to perform extensive numerical study for analyzing the anisotropic turbulence effects on spatial and temporal behaviors of diesel sprays after wall impingement. The turbulence model of Durbin is used for comparisons with the $k-\varepsilon$ model. The turbulence-induced dispersions of droplets are considered to describe the anisotropy of turbulence effectively and the spray/wall interactions are simulated using the model of Lee and Ryou. The present study investigates the internal structures of impinging diesel sprays such as Sauter mean diameter (SMD), loca1 droplet velocities, and local gas velocities and also compares the results predicted by two turbulence models with the experimental data. The Durbin's model considering the anisotropy of turbulence predicts both gas and droplet tangential velocities better than the$k-\varepsilon$ model does. It is concluded that the anisotropy of turbulence should be considered in simulating impinging diesel sprays.

• Journal of ILASS-Korea
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• v.2 no.1
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• pp.36-45
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• 1997

A spray-wall impingement model for fuel sprays is proposed and implemented as a module into the KIVA-POSTECH code. The model is based on the single droplet experiments. The droplet behaviors after impingement are determined from experimental correlations. Different behaviors of impinged droplets depend on the wall temperature and the critical temperature of the fuel. Fuel film formation is taken into account so that the model can be applicable to any wall temperature and injection conditions. Computational results on a normal and on inclined wall are in good agreement for the spray shape and penetration. More validation against experiments and development of the heat transfer model are needed for further improvement.

• Journal of ILASS-Korea
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• v.11 no.2
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• pp.75-80
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• 2006

The present article proposes a new droplet collision model including the stretching separation regime and the formation of satellite droplets. The new model consists of several equations to calculate the post-collision characteristics of colliding droplets and satellite droplets. These equations are derived from the energy balance of droplets between before and after collision. For binary collision of water droplets, the new model shows good agreement with experimental data far the number of satellite droplets.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.291-294
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• 2002

This study describes the external spray characteristics of deflector nozzle such as the breakup procedures of liquid sheet, spray angle, discharge coefficient and bubble behaviors of spray and SMD at deflector nozzle. In order to visualize the spray behaviors shadow graphy technique were used. According to the increase of injection pressure, development of the spray passes through the dribbling, distoted jet, closed bubble due to the contraction by surface tension forces, the bubble opens into hollow tulip shape, and the curved surface straightened to form a conical sheet like as the simplex swirl atomizer. Spray cone angle was nearly 90 deg. Variations of SMD were examined in order to describe the dependency of SMD on the injection pressure and orifice diameter. The shape of deflector and oriffice diameter had an effect on the discharge coefficient.