• Journal of ILASS-Korea
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• v.16 no.2
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• pp.104-109
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• 2011

The present study investigated experimentally the spreading characteristics of a single liquid impinging on the inclined micro-textured aluminum (Al 6061) surfaces manufactured by using a micro computerized numerical control (${\mu}$-CNC) milling machine. The textured surfaces were composed of patterned micro-holes (diameter of $125\;{\mu}m$ and depth of $125\;{\mu}m$). In our experiment, the de-ionized (DI) water droplet of $4.3\;{\mu}l$ was impinged normally on the non-textured and textured surfaces at two different Weber numbers, and the droplet impinged on the inclined surfaces with different angles. A high speed camera was used to capture sequential digital images for measurement of the maximum spreading distance. It was found that for the textured surface, the measured apparent equilibrium contact angle (ECA) increased up to $105.8^{\circ}$, higher than the measured ECA of $87.6^{\circ}$ for the non-textured (bare) surface. In addition, it is conjectured that the spreading distance decreased because of a liquid penetration during droplet spreading through the holes, the increase in hydrophobicity, and viscous dissipation during impact process.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.12
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• pp.1635-1646
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• 1997

The nozzle length to diameter ratio of real diesel nozzles is about 2-8 which is not long enough for a fully developed and stabilized flow. The characteristics of the flow such as turbulence at the nozzle exit which affect the development of the spray can be enhanced by impinging the flow inside nozzle. The flow details inside the impinging nozzles have been investigated both experimentally and numerically. The mean velocities, the fluctuating velocities, and discharge coefficients in the impinging inlet nozzles, round inlet nozzle, and sharp inlet nozzle were obtained at various Reynolds number. The developing feature of the external spray were photographed by still camera and the droplet sizes and velocities were also measured by laser Doppler technique. The spray angle was greater and the droplet sizes near the spray axis were smaller with the impinging flow inside nozzle.

• Journal of ILASS-Korea
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• v.17 no.1
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• pp.14-19
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• 2012

The present study conducts experimental investigation on spreading and deposition characteristics of a $4.3{\mu}l$ de-ionized (DI) water droplet impacting upon aluminum (Al 6061) flat and textured surfaces. The micro-textured surface consisted the micro-hole arrays (hole diameter: $125{\mu}m$, hole depth: $125{\mu}m$) fabricated by the conventional micro-computer numerical control (${\mu}$-CNC) milling machine process. We examined the surface effect of texture area fraction ${\varphi}_s$ ranging from 0 to 0.57 and impact velocity of droplet ranging from 0.40 m/s to 1.45 m/s on spreading and deposition characteristics from captured images. We used a high-speed camera to capture sequential images for investigate spreading characteristics and the image sensor to capture image of final equilibrium deposition droplet for analyze spreading diameter and contact angle. We found that the deposition droplet on textured surfaces have different wetting states. When the impact velocity is low, the non-wetting state partially exists, whereas over 0.64 m/s of impact velocity, totally wetting state is more prominent due to the increase kinetic energy of impinging droplet.

• Journal of ILASS-Korea
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• v.27 no.2
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• pp.77-83
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• 2022

In this study, the thickness of the liquid sheet formed by a low speed impinging jet onto a flat plate was measured by the direct contact method. The spatial distribution characteristics of the sheet thickness in the radial and circumferential directions, and the effects of jet velocity and liquid viscosity were analyzed. The measurement results were compared with the theoretical predictions. The wavy surface was observed in the case of low viscosity water, but not in the high viscosity aqueous glycerol solutions. The sheet thickness increased as the circumferential angle increased or the distance from the impinging point increased, but the thickness decreased as the circumferential angle increased around the impinging point. As the jet speed increased, the sheet thickness decreased, and the sheet thickness increased as the liquid viscosity increased. Comparison with the theoretical predictions showed that the measurement results agreed well in the case of low viscosity water or high viscosity liquids around the impinging point. The distribution characteristics of the sheet thickness can provide useful means for prediction of spray characteristics in splash plate injectors.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.3
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• pp.97-105
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• 1998

High pressure injection is recently used to reduce the emissions and increase the power of DI diesel engine. This high pressure injection makes the spray strike the cylinder wall. This spray/wall impingement is known to affect the emission and performance of DI diesel engine such that it is very important to know the spray/wall impingement process. In this study, multidimensional computer program KIVA-II was used to clarify the effect of spray wall impingement by different injection spray angle with the spray/wall impingement model consiedering rebound and slide motion and also the improved submodel for liquid breakup, drop distortion model.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.1
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• pp.62-68
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• 2005

An injector for fuel rich gas generator was designed and experimentally investigated. Five variations of F-O-F triplet impinging type injector were tested to evaluate spray characteristics with kerosene/water simulant propellant. Test was focused to find the effect of design variables of impinging angle, and impinging distance, on the atomization performance. A mixing efficiency is used to compare droplet distribution and local O/F ratio of each injector in the range of momentum ratio of 0.2~1.3. Test results shows the max value of mixing efficiency locates about the 0.8 in momentum ratio. And the injector with an impinging angle of 45 degree and impinging distance of 6mm shows the very good performance result suitable for fuel rich gas generator. A combustion test will be also conducted with selected injector to verify the spray pattern and mixing efficiency.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.10
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• pp.1285-1293
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• 2000

In port fuel injection system of SI engines, injected fuel is impinged onto the surface of intake valves and port-wall, and then formed the wall flow under the cold start operation. Wall flows entrained into the cylinder result in the unsteady and nonuniform mixture formation. Therefore, the spray impingement to the wall is considered as having negative influences such as lowering combustion efficiency and causing unburned hydrocarbon emissions. This study investigates the spray characteristics of the wall impinging air-assist spray in suction air flow. A PDPA was used to analyze the flow characteristics under the different conditions such as impingement angle and supplied air. Experimental data concerning the impinging sprays has been obtained in the vicinity of the wall. Measured droplets divided into the pre-impinging droplets which denote as the positive normal velocities and post-impinging droplets that describe as the negative normal velocities for the suction flow. Their velocities, size distributions and SMD are comparatively analyzed before and after the impingement.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.8
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• pp.69-76
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• 2003

For stable combustion and safety of a structure of the propulsion system, a cooling system to the liquid rocket engine should be incorporated. In this study, Eulerian-Lagrangian scheme for two phase combustion, nongray radiation and soot formation effect, and film-wall interaction have been introduced to study the effect of film cooling. After briefly introducing the governing equation, combustion characteristics with change of wall temperature has been investigated by varying such parameters as fuel mass fraction for film cooling, diameter of the fuel droplet, overall mixture fraction of oxygen to fuel. Also, radiative heat flux is compared with the conductive one at the combustor wall.

• Journal of ILASS-Korea
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• v.9 no.2
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• pp.1-8
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• 2004

This work was performed to investigate the distribution of the fuel droplet size around the bluff-body and the combustion characteristics. The geometry of the bluff-body influenced the spray shape and the combustion characteristics. Diameters of the bluff-body in this experiment are 6, 8, and 10 mm and the impingement $angles({\theta})\;are\;30^{\circ},\;60^{\circ},\;and\;90^{\circ}$. The measurement points were at the distances of 20 and 30 mm axially from the nozzle. The SMD and Rosin-Rammler distribution was acquired by image processing technique (PMAS), and the mean temperatures were measured by thermocouple. The results obtained are as follows; In the condition of ${\theta}=60^{\circ}$, the values of SMD are not greatly varied compared to the other conditions. As the impingement angle of bluff-body was increased, the high temperature region was wider along radial direction. When the air-fuel ratio was increased, the CO concentration was decreased.

• Journal of ILASS-Korea
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• v.4 no.3
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• pp.32-41
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• 1999

In this research, internal-mixing twin-fluid atomizer using sonic energy is designed and manufactured. We are trying to intimate high efficiency twin-fluid atomizer to obtain good liquid atomization in the low pressure region. Define of geometric form of atomizer, characteristics of spray is influenced by position, depth and height variation of cavity resonator, variation of sound intensity and resonant sound frequency with liquid flow rate. The liquid atomization is promoted by multi-stage disintegration of mixing flow of gas with liquid and the optimum condition of position and depth of cavity resonator according to sonic energy is obtained from the condition at a=2.5mm and L=2mm. The velocity distribution of droplets shows negative value due to recirculation region at the center of axial, and as the radial direction distance is far, the velocity distribution of droplets decrease slowly after having a maximum value. However velocity and SMD show nearly uniform distribution at the down stream and as result compared to Nukiyama and Tanasawa's equation. atomization of mixing flow with air and liquid dispersing from the outlet of the nozzle is promoted by the effect of collision at the cavity resonator.