• Journal of Advanced Marine Engineering and Technology
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• v.32 no.7
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• pp.1019-1029
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• 2008

In this study, visual investigation of sprays and flames has been performed and soot formation in Diesel and GTL fuels has been compared in a specially designed Rapid Charging Combustion Vessel (RCCV) under various ambient gas $O_2$ concentrations and two injection pressures. It has been concluded that soot in the mixing-controlled combustion of Diesel and GTL fuels has similar tendency to be formed in the leading portion of the jet boundaries. Auto-ignition delay for GTL fuel is shorter than that for diesel fuel. The temporal and special variation of soot concentration in the diesel flame jets at various $O_2$ concentrations was correlated with the heat release rate. Soot concentration appears in the regions when diffusion combustion starts, and its concentration reaches maximum at the peak of heat release curve and then decreases due to oxidation. Visualization by shadowgraph method showed that soot decreases with lower $O_2$ concentration, and higher injection pressure.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.4
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• pp.61-68
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• 2015

Reactive sprays of two propellant combinations(GOx/kerosene and $GN_2O$/ethanol) were observed and compared with each other as a basic research of visualizing supercritical combustion. A shadowgraph imaging method was used to visualize the reactive sprays, and shadowgraph images were converted to density gradient magnitude images to analyse the structure of reactive sprays. The gas-liquid interface of GOx/kerosene spray showed rougher boundary and steeper density gradient near the injector face than the $N_2O$/ethanol at similar combustion chamber pressure. Spray core length was calculated from averaged density gradient magnitude images and it was revealed that spray core length of GOx/kerosene was shorter than that of $GN_2O$/ethanol, although momentum flux ratio of GOx/kerosene propellant combination was lower.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.2
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• pp.41-47
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• 2017

By using liquid and gaseous nitrogen as simulants, effects of pintle opening distance and simulant supplying condition on spray from pintle injector were investigated qualitatively. The experiment was performed by fixing the liquid supply pressure and varying the opening of the pintle and the supply pressure of gaseous nitrogen. Shadowgraph method with CCD camera was used for image visualization, and the differences of liquid-gas spray were compared by image post processing. In case of liquid nitrogen single injection, as the opening distance was increased, the injection speed was decreased. Therefore, the end of liquid sheet were converged to the center of spray. In the case of liquid nitrogen/Gaseous nitrogen spray, although shadowgraph images look similar to each other, It is shown that it can be analysed by image post processing.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.4
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• pp.510-518
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• 1996

The study presents experimental and theoretical analysis focusing on the infulence of a noncondensable gas upon the absorption enhancement that is obtained by Marangoni convection generated by the addition of the surfactant. The shadowgraph method is adopted in this visualization. As a result of absorption phenomena with shadowgraph photos, the different patterns of Marangoni convection cells are observed in accordance with the various amounts of noncondensable gas. Furthermore, non dimensional number K(Ma/Ra) is introduced to calculate the value of surface tension difference theoretically for the comparison with the various amount of non condensable gas in absorber.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.5
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• pp.24-29
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• 2007

This study aims to provide a fundamental data for directly injected hydrogen fuel engines. Spray, ignition and combustion characteristics of hydrogen were studied using constant volume chamber. For spray visualization, hydrogen was vertically injected into a combustion chamber at various condition, for example, injection pressure, ambient pressure. And an argon laser was used for the shadowgraph photography by applying optical method. Also, to investigate heat-release rate and flame propagations, spark was ignited on hydrogen injected at the different time after injection and the duration of injection was also changed. Processes of ignition and combustion were analyzed by heat-release rate calculated by pressure history and were observed by shadowgraph photography The results gave much knowledge of spray, ignition and combustion characteristics of hydrogen.

• Journal of ILASS-Korea
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• v.18 no.3
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• pp.140-145
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• 2013

Sub/supercritical spray experiments were conducted, and cryogenic nitrogen and gaseous argon were selected for simulants. liquid nitrogen and gaseous argon were injected in subcritical case, and supercritical nitrogen and near-critical gaseous argon were injected in near-critical/supercritical cases. shadowgraph method was used to visualize spray, and analyzed about the breakup length. The breakup length was measured from numbers of Instantaneous shadowgraph Images from each case, and they were compared with momentum flux ratios and density ratios. It was observed that the relation between breakup length and momentum flux ratio was fitted into former experiment results. and the reasonable constant was suggested about the relation between breakup length and density ratio.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.784-788
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• 2004

A visualization study of shock formation of the supersonic jet nozzle using a Shadowgraph Method (SM) was carried out to investigate the effect of the longitudinal variation of coaxial pipe end tip position inside the supersonic nozzle. The experiment was performed for the Mach number range from 1.1 to 1.2 at nozzle exit. The well known shock cell structure was shown with the pipe end located deep inside the nozzle for the studied Mach number. With the pipe end approaches nozzle exit, it was found that the shock cell structure disappeared and turned into complex formation. In order to understand the mechanism of the shock structural change, computational simulation was carried out using the Navier-Stokes solver, FLUENT. Topological sketch was added with an aid of the visualization and the numerical simulation.

• Transactions of the Korean hydrogen and new energy society
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• v.16 no.1
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• pp.1-8
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• 2005

Transition of momentum-controlling hydrogen jet to buoyant jet is experimentally investigated in order to develop a prediction model for the moving trajectory of hydrogen leaked from hydrogen devices. In the experiments, room-temperature helium, that has a similar density to the hydrogen leaked from high pressure tank, is horizontally injected through a 4mm tube and its moving trajectory is visualized by the shadowgraph method. The moving trajectories are found to be parabolic, thereby exhibiting increasing influence of the buoyancy. In analyzing the experimental results, the vertical movement is assumed to be controlled by the buoyancy while the horizontal movement is controlled by the air entrainment caused by the initial momentum. The resealing based on this assumption yields a single curve fitting to the all experimental results.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.320-324
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• 2004

Laser Propulsion is a device that generates thrust using laser energy. Laser-driven In-Tube Accelerator (LITA) has been developed at Tohoku University. LITA is a laser propulsion system that accelerates an object not in an open air but in a tube. Experiments of vertical launching and pressure measurement on the tube wall were carried out and in order to observe the initial state of plasma and blast wave, the visualization experiment was carried out using the shadowgraph method. In this study, the time variation of pressure on the tube wall is numerically simulated solving Euler equation. In order to model the laser energy, heat source function added to the frozen flow Euler equation. Plasma size from the shadowgraph images was used for the initial condition of laser energy input. For verification of the modeling, these results were compared with the previous experimental and numerical results. From these verifications, an analysis of LITA performance will be investigated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.2
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• pp.197-204
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• 2012

We explore the evolution of metal plasma generated by high laser irradiances and its effect on the surrounding air by using shadowgraph images after laser pulse termination and X-ray diffraction (XRD) of aluminum plasma ablated by a high-power laser pulse (>1000 mJ/pulse) and oxygen from air. Hence, the formation of laser-supported detonation and combustion processes has been investigated. The essence of this paper is in observing the initiation of chemical reaction between the ablated aluminum plasma and oxygen from air by the high-power laser pulse (>1000 mJ/pulse) and in conducting a quantitative comparison of the chemically reactive laser-initiated waves with the classical detonation of an exploding aluminum (dust) cloud in air. The findings in this work may lead to a new method of initiating detonation from a metal sample in its bulk form without any need to mix nanoparticles with oxygen for initiation.