• Journal of Mechanical Science and Technology
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• 제16권7호
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• pp.999-1008
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• 2002

The spray structures and distribution characteristics of liquid and vapor phases in non-evaporating and evaporating Gasoline Direct Injection (GDI) fuel sprays were investigated using Laser Induced Exciplex Fluorescence (LIEF) technique. Dopants were 2% fluorobenzene and 9% DEMA (diethyl-methyl-amine) in 89% solution of hexane by volume. In order to study internal structure of the spray, droplet size and velocity under non-evaporating condition were measured by Phase Doppler Anemometry (PDA). Liquid and vapor phases were visualized at different moments after the start of injection. Experimental results showed that the spray could be divided into two regions by the fluorescence intensity of liquid phase: cone and mixing regions. Moreover, vortex flow of vapor phase was found in the mixing region. About 5㎛ diameter droplets were mostly distributed in the vortex flow region. Higher concentration of vapor phase due to vaporization of these droplets was distributed in this region. Particularly, higher concentration of vapor phase and lower one were balanced within the measurement area at 2ms after the start of injection.

• 대한기계학회논문집B
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• 제23권1호
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• pp.140-148
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• 1999

Experiments on flame spread in an one-dimensional droplet array up to supercritical pressures of fuel droplet have been conducted In normal gravity and microgravity. Evaporating process around unburnt droplet is observed through high-speed Schlieren and direct visualizations in detail, and flame spread rate is measured using high speed chemiluminescence images of OH radical. Flame spread behaviors are categorized into three: flame spread is continuous at low pressures and is regularly intermittent up to the critical pressure of fuel. flame spread is irregularly intermittent and zig-zag at supercritical pressures of fuel. At atmospheric pressure, the limit droplet spacing and the droplet spacing of maximum flame spread rate in microgravity are larger than those in normal gravity. In microgravity, the flame spread rate with the increase of ambient pressure decreases initially, takes a minimum, and then decreases after taking maximum. This is so because the flame spread time is determined by competing effects between the increased transfer time of thermal boundary layer due to reduced flame diameter and the reduced ignition delay time in terms of the increase of ambient pressure. Consequently, it is found that flame spread behaviors in microgravity are considerably different from those in normal gravity due to the absence of natural convection.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.353-358
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• 2000

To achieve the requirement for high fuel economy and low emissions, the research for GDI engines is recently very brisk in the whole world. This study was performed to measure distribution of average particle size in non-evaporating spray. The 2-D fluorescence/scattering images of fuel spray were captured simultaneously by visualization system composed of a laser sheet, a doubling prism, optical filters, and an ICCD camera. Using the ratio of the two light intensities, particle size distribution was obtained. The SMD measured by fluorescence/scattering technique was compared with it obtained by PDA. The experimental results show that the spray structure of GDI injector and temporal SMD distribution.

• 한국분무공학회지
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• 제5권1호
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• pp.13-22
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• 2000

The present study has numerically analyzed the vaporization characteristics of fuel droplets in the high temperature convective flow field. The axisymmetric governing equations for mass, momentum, energy, and species are solved by an iterative and implicite unstructured finite-volume method. The moving boundary due to vaporization is handled by the deformable unstructured grid technique. The pressure-velocity coupling in the density-variable flows is treated by the SIMPLEC algorithm. In terms of the matrix solver, Bi-CGSTAB is employed for the numerically efficient and stable convergence. The n-decane is used as a liquid fuel and the initial droplet temperature is 300K. Computations are performed for the nonevaporating and evaporating droplets with the relative interphase velocity(25m/s). The unsteady vaporization process has been simulated up to the nondimensional time, 25. Numerical results indicate that the mathematical model developed in this study succesfully simulates the main features of the droplet vaporization process in the convective environment.

• 대한기계학회논문집B
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• 제37권7호
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• pp.695-701
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• 2013

본 논문은 비이온의 계면 활성제에 의해 증발하는 물방울의 열모세관 유동(마랑고니 유동)이 억제되는 것을 실험적으로 검증한다. 물방울이 소수성 표면 위에서 증발할 때, 액적 내부의 마랑고니 유동을 관찰하였고, 계면 활성제 농도에 따라 이 유동이 억제되는 것을 조사하였다. 초기 계면 활성제 농도가 증가하면, 마랑고니 유동의 속도와 수명이 감소한다. 이 결과는 계면 활성제에 의해 액적 계면에서 점착 경계 조건이 성립됨을 보여주는데, 이것은 계면 점착 현상과 관련된 기존의 모델에 기초하여 설명되었다. 또한 액적의 초기 계면 활성제 농도가 임계 농도 이하일 때, 증발 초기 접촉선 비고정 현상을 발견했는데, 이것은 마랑고니 유동이 접촉각의 이력 현상을 감소시키기 때문이다.

• 동력기계공학회지
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• 제18권6호
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• pp.21-28
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• 2014

The studies of the spray characteristics for a CRDI engine had been advancing by many researchers, because the performance and exhaust emission were significantly affected with the spray characteristics. But most experiments of the studies would be done at low ambient pressure conditions under 2MPa. In this study, injection rates were measured with Zeuch's method at various ambient pressures to 5MPa and a constant injection pressure of 130MPa. On the same conditions, non-evaporating spray images were taken with a high speed camera and analyzed carefully with Adobe Photoshop CS3. Macroscopic spray characteristics and breakup processes in the spray could be found from the examined and analyzed data. The initial injection rate, penetration, angle, velocity and breakup of the spray were practically affected with a variation of the ambient pressure, but the injection start time and injection period were scarcely affected. As the ambient pressure was higher, the breakup of a high density droplet region in the spray was happened slowly and the main position of breakup was shifted from a front of the spray to a upstream around a nozzle. The results and techniques of spray visualization and injection rate measurement in this study would be practically effective to study a high pressure diesel spray for a CRDI.

• 오토저널
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• 제14권3호
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• pp.102-108
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• 1992

To clarify the structure of a diesel spray, a transient non-evaporating diesel spray injected under different ambient pressure and different injection pressure was studied. Spray tip penet- ration and spray angle were measured by taking the high speed shadowgraph of spray and Sauter mean Diameter(SMD) was also measured by light scattering technique at different positions along the spray axis and at different time from the start of injection. The effects of the operating parameters on the spray shape and SMD were investigated. By increasing the injection pressure, the spray tip penetration and the spray angle increased and the change of the ambient pressure also resulted in the considerable change in the shape of the spray. The analysis of SMD measurement showed that the atomization is a process that continues in sp- ace and time. As the injection pressure increases SMD decreases rapidly and with the increa- se of the ambient pressure the atomization process ends faster than the lower ambient press- ure and at lower pressure the atomization process continues to much farther downstream and far afterward.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.184-185
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• 2006

Two-step growth to incorporate the Mg atoms in the ZnO nanorods fabricate by thermal evaporation process and also utilized the ZnO film as a template. In the first step of low temperature, Zn seed metals with low melting temperature formed the droplet, and then MgZnO ternary nanorods were grown by injecting oxygen and evaporating Mg atoms in high temperature process of the second step. The vertical growth of the MgZnO nanorods with large-area distribution and uniformity was successfully performed on the ZnO template. We investigated the shape of the vertically grown 1-D MgZnO nanorods and characterized the optical and crystal properties. We confirmed the incorporation of Mg atoms by the EDS and PL spectrum.

• Journal of Advanced Marine Engineering and Technology
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• 제34권5호
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• pp.645-652
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• 2010

본 연구의 목적은 다양한 분위기 압력 하에서 커먼레일 디젤인젝터를 통해 분사되는 비증발 디젤 분무특성에 관한 연구이다. 디젤분무의 거시적 특성으로 분무관통거리와 분무각을 음영사진과 이미지프로세싱으로 연구하였다. 수치해석은 상용 CFD프로그램인 AVL-FIRE를 사용하였다. 분열모델은 WAVE모델을 사용하였으며 표준 $k-{\varepsilon}$난류모델을 적용하였다. 분무각과 Zeuch법을 적용한 연료 분사율을 수치해석의 입력값으로 사용하였다. 분무관통거리를 실험값과 비교하여 좋은 결과를 얻었고 수치해석을 통하여 노즐팁 하류방향으로 분무의 각 구간별 액적입경분포를 알아보았다.

• Korean Chemical Engineering Research
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• 제44권3호
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• pp.235-242
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• 2006

분무 열분해법이란 전구체를 용해시킨 용액을 수 마이크론에서 수십 마이크론 크기의 액적으로 분무한 후, 용매를 증발시키고 석출된 전구체를 열분해하여, 입자 및 필름을 제조하는 공정이다. 이 분무 열분해법의 핵심 요소는 전구체,용매, 액적 제조 그리고 분해 반응기 등 4가지이다. 이 4가지 요소의 적절한 조합에 의해서 현존하는 거의 대부분의 입자와 필름을 제조할 수 있는 범용성이 높은 기술이다. 현재 기술 수준으로는 상업적인 성공을 거두기는 힘들지만 향후 다성분계의 입자나 필름, 혹은 고기능성 입자의 제조에 응용될 경우 매우 유용한 기술로 각광을 받을 전망이다. 본 총설에서는 이 분문 열분해법을 이용해서 만들어지는 입자 중에서 주로 형광체를 중심으로 지금까지 개발된 다양한 분무 열분해 공정 기술을 소개한다