• 한국자동차공학회논문집
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• 제15권5호
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• pp.30-37
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• 2007

Dimethyl Ether(DME) is an alternative fuel for diesel engine, it is renewable and offers potential reductions in emissions. This work was conducted to figure out the macroscopic behavior and the atomization characteristics of DME using a common-rail injection system. The macroscopic behavior was visualized with the spray visualization system composed of a Nd;YAG laser and an ICCD camera. The atomization characteristics were investigated in terms of axial mean velocity, Sauter mean diameter(SMD) and droplet distributions obtained from a phase Doppler particle analyzer(PDPA) system. In this study, it was revealed that the macroscopic behavior and the atomization characteristics of DME are similar compared with commercial diesel fuel. However, DME fuel has a shorter spray tip penetration and a small SMD due to the effect of evaporation characteristics.

• 한국분무공학회지
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• 제25권3호
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• pp.111-118
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• 2020

This paper describes the effect of DME, biodiesel blended fuels on the macroscopic spray characteristics in a high pressure diesel injection system using Background Oriented Schlieren (BOS) method. The BOS method for visualization of impingement evaporation sprays to analyze macroscopic spray properties and evolutionary processes. In this work, the blending ratio of DME in the blended fuel are 0, 50, 100% by weight ratio. In order to investigate the macroscopic impinged spray characteristics under the various injection parameters and blending ratio. In this work, a mini-sac type single-hole nozzle injector with nozzle hole was length 0.7 mm and diameter of 0.3 mm was used. According to the result, the spray area of the collision wall increased as the DME mixing ratio increased, and the evolutionary pattern showed a stepwise increase due to the collision effect of the wall. Also, results of impinged spray area were increased according to increasing injection pressure.

• 한국분무공학회지
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• 제6권2호
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• pp.16-21
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• 2001

This paper describes the macroscopic behavior and atomization characteristics of the high-pressure gasoline swirl injector in direct-injection gasoline engine. The global spray behavior of fuel injector was visualized by shadowgraph technique. The atomization characteristics of gasoline spray such as mean diameter and mean velocity of droplets were measured by the phase Doppler particle analyzer system. The macroscopic visualization and experiment of particle measurement on the fuel spray were investigated at 7 and 10 MPa of injection pressure under different spray cone angle. The results of this work show that the geometry of injector was more dominant over the macroscopic characteristics of spray than the fuel injection pressure and injection duration. As for the atomization characteristics, the increase of injection pressure resulted in the decrease of fuel droplet diameter and the atomization characteristics differed as to the spray cone angle. The most droplets had under $25{\mu}m$ diameter and for the large droplets(upper $40{\mu}m$) as the spray grew the atomization presses were very slow. Comparison results between the measured droplet distribution and the droplet distribution functions revealed that the measured droplet distribution is very closed to the Normal distribution function and Nukiyama-Tanasawa's function.

• 한국분무공학회지
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• 제23권1호
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• pp.22-29
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• 2018

The purpose of this study is to investigate the macroscopic spray characteristics and spray pattern of a gasoline direct injection (GDI) injector according to the increase of injection pressure. The macroscopic spray characteristics, such as a spray tip penetration and spray angle, were measured and analyzed from the frozen spray images, which are obtained from the spray visualization system including the high-speed camera, light-source, long-distance microscope (LDM). The spray pattern was analyzed through the deviation of the center of the spray plum and images were acquired using Nd: YAG Laser and ICCD(Intensified charge coupled device) camera. From the experiment and analysis, it revealed that the injection pressure have a significant influence on the spray tip penetration and spray pattern. However, the injection pressure have little influence on the spray angle. The increase of injection pressure induced the reduction of a closing delay. In addition, the deviation of spray center increase with the increase of injection pressure and the distance from a nozzle tip.

• 대한화학회지
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• 제62권3호
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• pp.243-252
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• 2018

이 연구에서는 중학교 2학년 학생들의 물질의 특성에 대한 거시적, 미시적 수준의 개념을 비교하였다. 기초 입자 개념 검사와 녹는점, 용해도, 밀도 개념에 대한 거시적, 미시적 수준의 개념 검사를 개발하여 371명의 중학생들을 대상으로 실시하였다. 학생들의 응답을 거시적 수준과 미시적 수준의 개념 이해 여부에 따라 네 가지로 범주화하고 범주별 비율과 특징을 분석하였다. 연구 결과, 거시적 수준의 개념을 이해한 학생들은 미시적 수준에서 다양한 오개념을 가지고 있는 경우가 많았다. 많은 학생들은 물질의 특성과 관련한 미시적 수준의 개념뿐 아니라 거시적 수준의 개념 이해에도 어려움을 겪었다. 거시적 수준의 개념을 이해하지 못한 학생들은 대부분 미시적 수준에서 거시적 수준의 응답과 일치하는 응답을 하지 못하였다. 기초 입자 개념 문항에 옳은 응답을 한 학생들도 물질의 특성 관련 개념을 이해하는 데 어려움을 겪었으나, 거시적 수준의 개념을 이해한 경우 미시적 수준의 개념도 함께 이해한 비율이 높았다. 연구 결과를 바탕으로 물질의 특성 관련 개념의 효과적인 교수학습 및 향후 교육과정의 개선을 위한 교육적 시사점을 논의하였다.

• International Journal of Automotive Technology
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• 제4권4호
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• pp.157-164
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• 2003

An experimental and numerical study was performed to investigate the macroscopic and microscopic atomization characteristics of high-speed diesel spray issued from the common-rail injection system. For the experiments, spray visualization system and a phase Doppler particle analyzer system were utilized to obtain the spray atomization characteristics such as the process of spray development, spray tip penetration, and SMD distribution. In order to analyze the process of spray atomization with KIVA-3 code, the TAB breakup model is changed to the KH-DDB competition model, which assumes the competition between the wave instability and droplet deformation causes the droplet breakup above the breakup length. The calculated results were also compared with the experiments in terms of spray tip penetration and SMD distribution. The results provide the process of spray development, axial and radial distribution of SMD, and calculated overall SMD as a function of time after start of injection.

• 한국분무공학회지
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• 제24권1호
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• pp.1-7
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• 2019

This study was carried out to analyze the spray characteristics as a function of the operating parameters of urea injector used in Urea-SCR system of passenger diesel vehicle. Spray visualization and PDPA experiment were performed to analyze the macroscopic spray development and atomization performance of urea-water-solution. For the urea injector, the deformation of the spray head does not appear to be significant because it operates at a low pressure conditions, and the liquid core and primary droplet are observed throughout the operating conditions. No increase in atomization is seen when the operating pressure is increased, and the spray develops linearly due to poor atomization characteristics. The macroscopic spray behavior of the low-pressure urea injector is predictable through the modification of the Hiroyasu equation.

• Journal of Mechanical Science and Technology
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• 제18권7호
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• pp.1222-1235
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• 2004

This study examines the influence of geometry on the internal flow and macroscopic behavior of the spray in Diesel nozzles. For this investigation, two bi-orifice nozzles were employed: one cylindrical and one conical. The first step is to use a non-destructive characterization method which is based on the production of silicone moulds so that the precise internal geometry of the two nozzles can be measured. At this stage the nozzles have been characterized dimensionally and therefore the internal flow can be studied using CFD calculations. The results gained from this experiment make it possible also to ascertain the critical cavitation conditions. Once the critical cavitation conditions have been identified, the macroscopic parameters of the spray can be studied in both cavitating and non-cavitating conditions using a test rig pressurized with nitrogen and with the help of a image acquisition system and image processing software. Consequently, research can be carried out to determine the influence that cavitation has on macroscopic spray behavior. From the point of view of the spray macroscopic behavior, the main conclusion of the paper is that cavitation leads to an increment of the spray cone angle. On the other hand, from the point of view of the internal flow, the hole outlet velocity increases when cavitation appears. This phenomenon can be explained by the reduction in the cross section of the liquid phase in the outlet section of the hole.

• Structural Engineering and Mechanics
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• 제19권5호
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• pp.519-533
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• 2005

The numerical simulations on the influence of mesoscopic structures on the macroscopic strength and fracture characteristics are carried out based on that the concrete is assumed to be a three-phase composite composed of matrix (mortar), aggregate and bond between them by using a numerical code named MFPA. The finite element program is employed as the basic stress analysis tool when the elastic damage mechanics is used to describe the constitutive law of meso-level element and the maximum tensile strain criterion and Mohr-Coulomb criterion are utilized as damage threshold. It can be found from the numerical results that the bond between matrix and aggregate has a significant effect on the macroscopic mechanical performance of concrete.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2000년도 제21회 KOSCO SYMPOSIUM 논문집
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• pp.194-201
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• 2000

This paper is intended to analyze the macroscopic behavior and transient atomization characteristics of the high-pressure gasoline injector in direct-injection gasoline engine. The global spray behavior of fuel injector was visualized by shadowgraph technique. Time-resolved droplet axial and radial velocity components and droplet diameter were measured at many probe positions in both axial and radial directions by a two-component phase Doppler particle analyzer (PDPA). In order to obtain the influence of fuel injection pressure, the macroscopic visualization and experiment of particle measurement on the fuel spray were investigated at 3,5 and 7 MPa of injection pressure under different surrounding pressure in the spray chamber. The results of this work show that the fuel injection pressure of gasoline injector in GDI engine has influence upon the mean droplet diameter, mean velocity of spray droplet, the spray tip penetration, and spray width under the elevated ambient pressure.