• Journal of ILASS-Korea
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• v.14 no.3
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• pp.117-121
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• 2009

Biodiesel fuel has different spray patterns, because viscosity and surface tension of biodiesel fuel are higher than that of diesel fuel. The diesel combustion is strongly controlled by the fuel spray behavior in combustion chamber. So, it was needed to understand the spay characteristics of non-esterification biodiesel fuel. In this study, the spray characteristics of non-esterification biodiesel fuel was investigated to confirm of an effect of WDP. The characteristics of fuel atomization was analyzed with SMD and span factor through laser diffraction particle analyzer (LDPA), and the process of spray injection was visualized through the visualization system composed of a halogen lamp and high speed camera. It was found that injection delay time and SMD of blended fuel with WDP get shoter and smaller than that of non-esterification biodiesel fuel.

• Journal of ILASS-Korea
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• v.7 no.3
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• pp.1-6
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• 2002

In this study numerical and experimental study on the spray atomization characteristics of a GDI injector is performed. To carry out numerical analysis, four hybrid models that are composed of conical sheet disintegration model, LISA model, DDB model, and RT model are used. The experimental results to evaluate the prediction accuracy of hybrid models are obtained by using phase Doppler particle analyzer and spray visualization system. It is shown that the prediction accuracy of hybrid model concerning spray developing process and spray tip penetration is good for all hybrid models, but the hybrid breakup models show different prediction of accuracy in the case of local radial SMD distribution.

• Journal of ILASS-Korea
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• v.15 no.1
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• pp.25-30
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• 2010

The capability of pilot injection with small fuel quantity at all engine operating conditions is one of the main feature of the common rail direct injection system. The purpose of the pilot injection is to lower the engine noise and to reduce the NOx emissions. This study describes the pilot spray structure characteristics of the common-rail diesel injectors with different electric driving characteristics, including solenoid-driven and piezo-driven type. Namely three common-rail injectors with different electric current wave were investigated in this study. The pilot spray characteristics such as spray speed, spray tip penetration, and spray angle were obtained by spray images, which is measured by the back diffusion light illumination method with optical system for high-speed temporal photography. As this research results, it was found that pilot injection of common-rail system was effected by rate of injection with different electrical characteristic for driving the injector.

• Journal of ILASS-Korea
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• v.25 no.1
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• pp.15-20
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• 2020

This study aims to investigate injection rate and microscopic spray characteristics of diesel fuel containing fine air bubble (FBD). fine bubble was generated by cavitation theory using bubble generator. Fuel spray was injected into constant volume chamber and visualized by high speed camera. The injection rate data was acquired with bosch tube method. Injection rate of finebubble diesel was very similar with that of diesel. It showed slightly faster injection start by 5 ㎲ attributed to the low viscosity characteristics. In microscopic spray visualization, fine bubble diesel spray showed unsymmetric spray shape compared with diesel spray. It also showed very vigorous spray atomization performance during initial spray development. Improved atomization was also attributed to the low viscosity and surface tension of finebubble diesel fuel.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.6
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• pp.450-455
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• 2002

Convective instability driven by surface tension is analyzed in an initially quiescent water absorbing ammonia gas using the linear stability theory. The propagation theory is adapated to find the critical conditions of the onset of solutal Maragoni convection. In this theory, the solutal penetration depth is chosen as the length scale factor. The results show that the liquid layer becomes more stable with decreasing the Schmidt number It is interesting that for a smaller Biot number than 100, the system becomes stable with decreasing Bi but for a larger Bi, it becomes unstable with decreasing Bi.

• Journal of ILASS-Korea
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• v.22 no.1
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• pp.29-35
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• 2017

This paper describes the effects of spray breakup model constants on spray and combustion characteristics in single cylinder compression engine. KIVA-3V code coupled with a CHEMKIN chemistry solver was used for numerical analysis. In this study, spray simulations and combustion simulations are studied simultaneously. Spray simulation was conducted in constant volume to reduce the effects of air-flow as swirl or tumble. The model validation was conducted and there are little difference between experiments and simulation, this differences were reasonable. In spray simulation, the effects of model constants on spray tip penetration, spray patter and SMD were studied. Furthermore, the analysis of effects of breakup variables on combustion and emissions characteristics was conducted. The results show the KH-RT breakup model constants affects spray and combustion characteristics strongly. Increasing KH model variable (B1) and RT model constants ($C_{\tau}$, $C_{RT}$) induced slower breakup time.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.142-145
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• 2003

In order to investigate the effect of cryogenic rolling on the critical current density (Jc), 54 and 55-multi-filament Bi-2223/hg tapes have been fabricated using a PIT process including two different types of cooling methods. The densification of oxide filament was found to occur due to the cryogenic rolling, and this enhanced the critical current density. However, when the wire was fully immersed in liquid nitrogen used as the coolant in cryogenic rolling, Jc degradation appeared caused by the nitrogen penetration into the filament. The cryogenically rolled tape with an improved type of cooling showed approximately 10％ Jc's increase.

• Journal of the Korean Society of Marine Environment & Safety
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• v.3 no.2
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• pp.13-21
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• 1997

This paper describes the effectiveness of laser pulse shaping in eliminating weld defects such as porosity, cracks and undercuts in pulsed Nd:YAG Laser welding. A large porosity was formed in a keyhole mode of deep penetration weld metal of any stainless steel. Solidification cracks were present in Type 303 with about 0.3%s. The conditions for the formation of porosity were determined in further detail in Type 316. With the objectives of obtaining a fundamental knowledge of formation and prevention of weld defects, the fusion and solidification behavior of a molten puddle was observed during laser spot welding of Type 310S. through high speed video photographing technique. It was deduced that cellular dendrite tips grew rapidly from the bottom to the surface, and consequently residual liquid remained at the grain boundaries in wide regions and enhanced the solidification cracking susceptibility. Several laser pulse shapes were investigated and optimum pulse shapes were proposed for the reduction and prevention of porosity and solidification cracking.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.2
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• pp.181-191
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• 2002

Spray calculation has been studied to understand the behavior of the spray in a combustion chamber But the spray dispersion has not been predicted properly in a high velocity injection spray or a wall impaction spray. In this study the extended grazing collision model is applied to improve the problem. The gas phase is modelled by the Eulerian continuum conservation equations of mass, momentum, energy and fuel vapour fraction. The liquid phase is modelled following the discrete droplet model approach in Lagrangian form. The droplet distributions, penetration, width and gas flows are compared for the cases with or without extended model. The extended collision model makes the results better.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.05a
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• pp.269-274
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• 1999

Aluminum alloy has not only physical characteristic of very high activated high thermal conductivity and high thermal coefficient expansion but also special characteristic of great difference fusibility of hydrogen between liquid and solid phase. Because of these reasons, Aluminum welding is very different. Therefore, only MIG welding method should be applied instead of other welding methods. In this study, in order to select optimal welding conditions, it has been to investigate the effectiveness on the welding current, welding speed, flow rate of gas and welding voltage to occurrence of spatters, external shape of bead, state of penetration and width and hight of bead by using filer metal of A15356(dia. 1.21mm) on the base material of A16061.