• Journal of ILASS-Korea
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• v.12 no.3
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• pp.154-159
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• 2007

Spray tip penetration and spray angle for one main injection were measured at the atmospheric condition with the fuel injection pressure of 270 bar and 540 bar. It investigates an effect of different nozzle hole geometry of conventional cylindrical one and those of elliptical ones. Injection period represented by injector pulse drive was fixed at 1ms. From the result of this study, it is shown that spray tip penetration becomes shorter and spray angle becomes wider with the elliptical nozzle hole geometry due to fast break-up of a fuel liquid column.

• Journal of ILASS-Korea
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• v.10 no.1
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• pp.24-34
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• 2005

Injection technology is one of the important technologies in a diesel engine. Many studies have done on the injection system. In this study, the fuel chamber geometry, the orifice ratio and the needle lift of the injection valve for a marine diesel engine are varied, and simulated. The result shows that the nozzle hole size has influence on the rail pressure and injection duration sensitively. The decrease of the static pressure at the nozzle hole entrance and the increase of the dynamic pressure on the outlet surface are occurred with the increase of the nozzle hole diameter. The highest dynamic pressure of the outlet was occurred at the needle lift of 0.4mm and the nozzle hole diameter of 0.328mm in this test nozzle.

• Journal of ILASS-Korea
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• v.20 no.4
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• pp.254-260
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• 2015

The objective of this study is to investigate the effect of multi-hole nozzle on the performance of small CRDI engine. Combustion and exhaust emission characteristics of engine were studied by using CFD simulation with ECFM-3Z combustion model. The conditions of simulation were varied with nozzle geometry, injection timing and injection quantity. In addition, the results were compared in terms of combustion pressure, rate of heat release, $NO_x$ and soot emissions. It was found that combustion pressure was increased when injection timing was advanced. The rate of heat release of 6 hole nozzle was higher than that of 12 hole nozzle since the quantity of fuel impinged at the bottom of piston rim was different under different injection timing conditions. In the case of $NO_x$ emission, 6 hole nozzle generated more $NO_x$ emission than 12 hole nozzle. On the other hand, in the case of soot emission, 12 hole nozzle showed higher value than 6 hole nozzle because injected fuel droplets from multi-hole nozzle were coalesced.

• International Journal of Automotive Technology
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• v.7 no.3
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• pp.283-288
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• 2006

A mathematical methodology is proposed for designing nozzle hole shapes producing controlled geometric cavitation. The proposed methodology uses an unstructured RANS flow solver, with the ability to compute sensitivity derivatives via an adjoint algorithm. The adjoint formulation for the N-S equations is presented while variation of the turbulence viscosity is not taken into account during the geometry modifications. The sensitivities are calculated in a mode independently of the shape parameterisation. The method is used to develop and evaluate conceptual shapes for nozzle hole cavitation reduction. The localized region at the hole inlet producing cavitation, is parameterised using its radius of curvature, while a cost function is formulated to eliminate the negative pressures present at this location. Sensitivity derivatives are used to assess the dependence of the localized region on the minimum pressure, and to drive the geometry to the targeted shape. The results show that the computer model can provide nozzle hole entry shapes that produce predefined flow characteristics, and thus can be used as an inverse design tool for nozzle hole cavitation control.

• Journal of the Korean Solar Energy Society
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• v.35 no.1
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• pp.69-80
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• 2015

A series of numerical analyses was conducted to predict the thermal performance of a solar air heater depending on the hole configuration and geometry in the absorber plate. The planar dimensions of the prototype were 1 m (W) by 1.6 m (H), and the maximum air flow considered was $187m^3/h$. It was considered that protruding holes with a triangular opening in the absorber plate would invoke turbulence in the air flow to enhance the convection heat transfer. Six different hole configurations were investigated and compared with each other, while the hole opening height was considered as a design variable. Three-dimensional transient analyses were performed with a commercial software package on the airflow and heat transfer in the model. The numerical results were analyzed and compared from the view point of the outlet air temperature and its time response to derive the optimal hole pattern and hole opening height.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.530-533
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• 2010

This paper presents numerical analysis and design optimization of various turbine blade cooling techniques with three-dimensional Reynolds-averaged Navier-Stokes(RANS) analysis. The fluid flow and heat transfer have been performed using ANSYS-CFX 11.0. A fan-shaped hole for film-cooling has been carried out to improve film-cooling effectiveness with the radial basis neural network method. The injection angle of hole, lateral expansion angle of hole and ratio of length-to-diameter of the hole are chosen as design variables and spatially averaged film-cooling effectiveness is considered as an objective function which is to be maximized. The impingement jet cooling has been performed to investigate heat transfer characteristic with geometry variables. Distance between jet nozzle exit and impingement plate, inclination of nozzle and aspect ratio of nozzle hole are considered as geometry variables. The area averaged Nusselt number is evaluated each geometry variables. A rotating rectangular channel with staggered array pin-fins has been investigated to increase heat transfer performance ad to decrease friction loss using KRG modeling. Two non-dimensional variables, the ratio of the eight diameter of the pin-fins and ratio of the spacing between the pin-fins to diameter of the pin-fins selected as design variables. A rotating rectangular channel with staggered dimples on opposite walls are formulated numerically to enhance heat transfer performance. The ratio of the dimple depth and dimple diameter are selected as geometry variables.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.8
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• pp.997-1002
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• 2012

Emission regulations have been strengthened step by step for marine engines. A noble measure is required both inside and outside of the combustion chamber. The combustion characteristics in cylinder have a very close relationship with the exhaust emission characteristics. Injection valve and nozzle hole geometry is an important factor for combustion. The study to improve the spray characteristics has concentrated on nozzle inlet geometry and nozzle hole diameter, but the exit geometry has not considered. In this study the nozzle exit angle variation was tested. The results show that the angle between $30^{\circ}$ and $60^{\circ}$ is more effective than the other cases.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.9-12
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• 2002

A parametric study has been conducted to investigate the effect of the geometry on the strength of an unidirectional and fabric hybrid laminated composite joint. Tests are conducted for the specimens with nine different edge-to-hole diameter or width-to-hole diameter ratios. For the finite element analysis, the characteristic length method is used, and the tests for determining the characteristic length are performed additionally. Nonlinear contact problem between the pin and laminate is modeled by the gap element in MSC/NASTRAN. Tsai-Wu failure criteria is applied to the stress on the characteristic curve. The finite element and experimental results shows good agreement in strength of composite joint. Results of the parametric study shows the effect of the geometry is remarkable in the specimens with width-to-hole diameter ratio less than 2.8 and edge-to-hole diameter ratio less than 1.4.

• Journal of The Korean Astronomical Society
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• v.34 no.4
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• pp.301-303
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• 2001

We suggest a possible scenario of an astrophysical black hole with non-vanishing electric charge and magnetic flux. The equilibrium charge on a rotating black hole in a force-free magnetosphere is calculated to be Q $\~$ BJ with a horizon flux of ${\~}BM^2$, which is not large enough to disturb the background Kerr geometry. Being similar to the electric charge of a magnetar, in sign and order of magnitude, both electric charge and magnetic flux are supposed to be continuous onto a black hole.

• Tunnel and Underground Space
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• v.20 no.1
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• pp.65-72
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• 2010

Crack-controlled blasting method which utilizes notched charge hole has been proposed in order to achieve smooth fracture plane and minimize the excavation damage zone. In this study, the blast models, which have a notched charge hole, were analyzed using dynamic fracture process analysis software to investigate the effect of the geometry of a notched charge hole and decoupling indexes of the charge hole on crack growth control in blasting. As a result, crack extension increased and damage crack decreased with the notch length. Ultimately, stress increment factors and resultant fracture patterns with different notch length and width were analyzed in order to examine the effect factors on the crack growth controlling in rock blasts using a notched charge hole.