• Journal of ILASS-Korea
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• v.20 no.1
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• pp.43-52
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• 2015

Experimental study was conducted to investigate the effects of ultra-high injection pressure and nozzle hole diameter on diesel flow and spray characteristics. Electronically controlled ultra-high pressure fuel injection system was made to supply the fuel of ultra-high pressure consistently. Three injection pressures, 80, 160, and 250MPa were applied. Four type of injectors with identical eight nozzle holes were used. The four injectors have nozzle hole diameters of 115, 105, 95, and $85{\mu}m$ respectively. Injection quantity and rate were measured to investigate flow characteristics according to injection pressures and nozzle hole diameters. Mie-scattering and shadowgraph were performed to visualize liquid and vapor phases of diesel spray in a constant volume combustion chamber (CVCC). Ambient conditions of high pressure and high temperature in a diesel engine were simulated by using CVCC.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.1
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• pp.16-22
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• 2008

The effect of two-phase spray injected into subsonic cross-flow was studied experimentally. External-mixing of two-phase spray from orifice nozzle with L/d of 3 was tested with various air-liquid ratio that ranges from 0 to 59.4%. Trajectory of spray and breakup phenomena were investigated by shadowgraph photography. Detailed spray structure was characterized in terms of SMD, droplet velocity, and volume flux using PDPA. Experimental results indicate that penetration length was increased and collision point of liquid jets approached to nozzle exit and distributions of mist-like spray were obtained by increasing air-liquid ratio.

• Journal of the Korean Society of Visualization
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• v.8 no.1
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• pp.19-24
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• 2010

Five different size of orifice were applied in a constant volume combustion chamber for evaluating the effects of torch-ignition on combustion. The initial flame development and flame propagation were analyzed by the mass burned fraction and combustion enhancement rate. The combustion pressures were measured to calculate the mass burned fractions and the combustion enhancement rates. In addition, the flame propagations were visualized by the shadowgraph method for the qualitative comparison. The result showed that the combustion pressure and mass burned fraction were increased when using the torch-ignition device. The combustion enhancement rates of torch-ignition cases were improved in comparison with conventional spark ignition. Finally, the visualization results showed that the torch-ignition induced faster burn than conventional spark ignition due to the earlier transition to turbulent flame and larger flame surface, during the initial stage.

• Journal of ILASS-Korea
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• v.10 no.4
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• pp.47-53
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• 2005

This paper presents the effects of ambient pressure on atomization characteristics of high-Pressure injector in a direct injection gasoline engine both experimentally and numerically. The atomization characteristics such as mean droplet size, mean velocity, and velocity distribution were measured by phase Doppler particle analyzer. The spray development, spray penetration, and global spray structure were visualized using a shadowgraph technique. In order to investigate the atomization process numerically, the LISA-DDB hybrid model was utilized. This breakup model assumes that the primary breakup occurs when the amplitude of the unstable waves is equal to the radius of the ligament of liquid sheet near the nozzle and the droplet deformation induces the secondary breakup. The results provide the effect of ambient pressure on the macroscopic and microscopic behaviors such as spray development, spray penetration, mean droplet size, and mean velocity distribution. It is also revealed that the accuracy of prediction of LISA-DDB hybrid model is pretty good in terms of spray developing process, spray tip penetration, and SMD distribution.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.192-197
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• 2004

Recently, fluidic thrust vectoring methods have been preferably employed to control the movement of propulsive systems due to relatively simpler design and lower cost than mechanical thrust vectoring methods. For An application of the thrust vectoring to flight bodies, it is necessary to understand very complicated exhaust flows which are often subject to shock waves and boundary layer separation. But researches for the thrust vector control using counterflow have been few. In the present study, experiments have been performed to investigate the characteristics of supersonic jets controlled by a thrust vectoring method using counterflow. The primary jet is expanded through a two-dimensional primary nozzle shrouded by collars, and is deflected by the suction of the air near nozzle into an upper slot placed between the primary nozzle and the upper collar. A shadowgraph method is used to visualize the supersonic jet flowfields. Primary nozzle pressure ratios and suction nozzle pressure ratios are varied from 3.0 to 5.0, and from 0.2 to 1.0 respectively. The present experimental results showed that, for a given primary nozzle pressure ratio, a decrease in the suction nozzle pressure ratio produced an increased thrust vector angle. As the suction nozzle pressure ratios were increased and decreased, the hysteresis of the thrust vectoring was observed through the wall pressure distributions

• Journal of Electrical Engineering and Technology
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• v.13 no.5
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• pp.2011-2016
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• 2018

In this study, we have been investigated pin to plate pulsed bi-polar discharges in saline solutions, where bubble generation occurs. We integrate basic I-V-t electrical characteristics with the ICCD shadowgraph images, and finally instant and time averaged I-V waveforms. We observed that the bubble formation phase dynamics is quite different corresponding to the polarity applied to the pin electrode. When the pin electrode is a cathode, the bubble tends to be periodically detached from the pin electrode and the numerous tiny voltage spikes occur related to the electron emission from a pin cathode casing via, we judge from, direct dissociation of water molecules by energetic electrons. On the contrary, the bubble tends to stick to the pin electrode, when the pin electrode is anode; the bubble grows in size throughout the pulse duration. The dynamic electrical characteristics relative to the applied polarity of a pin electrode are presented and discussed by analysis of time averaged I-V waveforms.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.2
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• pp.304-313
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• 1987

The behaviors of layers developed in a solar pond were studied by experimental and analytical methods. An experimental solar pond heated from below was constructed and operated at the net heat fluxes of 110 and 160W/m$^{2}$ and at the initial salt concentration gradients of 18.2, 27.3 and 36.4%/m. The thicknesses, growth rates, temperature and salt concentration in the top and the bottom mixed layers, the diffusive layer and the upper and the lower interfacial boundary layers were measured. The shadowgraph technique was used in order to observe all layer formation and an electroconductivity-temperature probe consisting of four electrodes was fabricated and used in measuring the salt concentration. Based on the experimental results, a model for the solar pond was developed and the governing equation and the assumptions were established. The governing equations were solved by the numerical method. The calculated results obtained from the analysis were compared with the experimental results.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.486-491
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• 2008

The spray characteristics and drop size measurements have been experimentally studied in liquid jets injected into subsonic crossflow. With water as fuel injection velocity, injection angle and atomizer internal flows were varied to provide of jet operation conditions. The injector internal flow was classified as three modes such as a non-cavitation flow, cavitation, and hydraulic flip flows. Pulsed Shadowgraph Photography measurement was used to determine the spatial distribution of the spray droplet diameter in a subsonic crossflow of air. And this study also obtains the SMD(Sauter Mean Diameters) distribution by using PLLIF(Planar Liquid Laser Induced Fluorescence) technique. The objectives of this research are getting a droplet distribution and drop size measurement of each condition and compare with the other flows effect. As the result, This research have been showed the droplet size were spatially dependent on air-stream velocity, fuel injection velocity, injection angle effects and normalized distance from the injector exit length.(x/d, y/d)There are also different droplet size characteristics between cavitation, hydraulic flip and the non-cavitation flows.

• Journal of Ocean Engineering and Technology
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• v.30 no.1
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• pp.44-50
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• 2016

An experimental study was performed to investigate the behavior of green water on a structure with a rectangular cross section under wave conditions, along with the flow characteristics in bubbly water flow. An experiment was conducted in a two-dimensional wave flume using an acrylic model (1/125) of FPSO BW Pioneer operating in the Gulf of Mexico under its design wave condition. The occurrence of green water, including its development, in front of the model was captured using a high-speed Charge Coupled Device (CCD) camera with the shadowgraph technique. Using consecutive images, the generation procedure for green water on the model was divided into five phases: flip through, air entrapment, wave run-up, wave overturning, and water shipping. In addition, the distinct water elevations of the green water were defined as the height of flip through, height of splashing jet, and height of freeboard exceedance, and showed a linear relationship with the incoming wave height.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.4
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• pp.330-340
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• 2018

In the present works, the High-speed Cavitation Tunnel (HCT) has been designed and manufactured to have the large test section to conduct various supercavitation experiments. The large amount of air ventilated behind a cavitator produces lots of tiny bubbles, which prevent clear observation of supercavitation at the test section. To collect small bubbles effectively, a bubble collecting section of large volume is equipped upstream of the test section. HCT has the test section dimension of $0.3^H{\times}0.3^W{\times}3.0^L\;m^3$ and provides maximum flow speed of 20.4 m/s at the test section. The blockage and Froude effects on the ventilated supercavitation are investigated successfully at the test section. The basic studies such as the supercavitation evolution, drag measurements and cavity shape extraction with air flow rate are also carried out in HCT.