• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.9
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• pp.711-716
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• 2020

Injection visualization of heated mixed simulant droplets based on hydrocarbon fuel was performed under supercritical state environment. Mixed simulant consisted of Decane and Methylcyclohexane with different critical pressure and critical temperature. Flows injected into the supercritical state environment created droplet by Rayleigh breakup mechanism, and the Oh number and Re number were determined to confirm the breakup area. The temperature of the mixed simulant varied from Tr=0.49 to Tr=1.34. The flow rate was maintained at 0.7 to 0.8 g/s. Droplet became shorter in breakup length as heated and into a lumped form. Second droplet was formed and when Tr=1.34, the phase was not visible in the supercritical state with local unsteady flow.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.253-256
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• 2009

In the micro turbojet engine less than 350kw power class, it is not easy to find out the good atomization fuel injector with good spray quality. However conceptually, rotating fuel injection system can give high atomization quality by only the centrifugal force of a high speed rotating shaft of the engine without high-pressure fuel pump. With this motivation, we manufactured very small rotating fuel injector of 40 mm diameter and performed under a variety of injection orifices. We measured droplet size, velocity and spray distribution by the PDPA(Phase Doppler Particle Analyzer) system. Also spray was visualized by using high speed camera. From the test results, we could understand that the length of liquid column from the injection orifice is mainly controlled by the rotational speeds. Furthermore, droplet size(SMD) is decreased with the rotational speeds and is influenced by the diameter of the injection orifice and liquid film thickness.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.6
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• pp.60-65
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• 2004

Numerical simulations and experiments have been carried out to investigate the effect of fuel injection nozzles on the combustion and NOx formation processes in a medium-speed marine diesel engine. Spray visualization experiment was performed in the constant-volume high-pressure chamber to verify the numerical results on the spray characteristics such as spray angle and spray tip penetration. Time-resolved spray behaviors were captured by high-speed digital camera and analyzed to extract the information on the spray parameters. Spray and combustion phenomena were examined numerically using FIRE code. Wave breakup and Zeldovich models were adopted to describe the atomization characteristics and NOx formation processes. Numerical results were verified with experimental data such as cylinder pressure, heat release rate and NOx emission. Finally, the effects of fuel injection nozzles on the engine performance were investigated numerically to find the optimum nozzle parameters such as fuel injection angle, nozzle hole diameter and number of nozzle holes. From this study, the optimum fuel injection nozzle (nozzle hole diameter, 0.32 mm, number of nozzle holes, 8 and fuel injection angle, $148^{\circ}$) was selected to reduce both the fuel consumption and NOx emission. The reason for this selection could be explained from the highest fuel-air mixing in the early phase of injection due to the longest spray tip penetration and the highest heat release rate after $19^{\circ}$ ATDC due to the increased injection duration.

• Composites Research
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• v.30 no.2
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• pp.84-93
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• 2017

This study investigates thermal and mechanical characterization of environmental barrier coating on the $SiC_f-SiC$ composites. The spherical environmental barrier coating (EBC) powders are prepared using a spray drying process for flowing easily during coating process. The powders consisting of mullite and 12 wt% of Ytterbium silicate are air plasma sprayed on the Si bondcoat on the LSI SiC fiber reinforced SiC composite substrate for protecting the composites from oxidation and water vapor reaction. We vary the process parameter of spray distance during air plasma spray of powders, 100, 120 and 140 mm. After that, we performed the thermal durability tests by thermal annealing test at $1100^{\circ}C$ for 100hr and thermal shock test from $1200^{\circ}C$ for 3000 cycles. As a result, the interface delamination of EBC never occur during thermal durability tests while stable cracks are prominent on the coating layer. The crack density and crack length depend on the spray distance during coating. The post indentation test indicates thermal tests influence on the indentation load-displacement mechanical behavior.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.49 no.6
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• pp.447-451
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• 2004

This study was conducted to establish the proper techniques of the recirculating wick hydroponics for safe seed tuber proliferation of potatoes (Solanum tuberosum L. CV. Dejima). To achieve these, several intact tubers (5, 10 and 20 g) and cut seed-pieces (two or four) were treated in wick hydroponic system beds. A polystyrene box (31cm in width, 20cm in height, 51cm in length, and $0.031m^3$ in volume) was placed on a styrofoam hox. Eight wicks $(width\;1.5cm\;{\times}\;length\;40cm) $ were put into each polystyrene hox and the boxes were filled with perlite + peatmoss (1 : 2, v/v) medium. Top fresh weight per plant increased with increasing the tuber size from 10 to 30g/tuber. As the tuber size increases from 10 to 30 g/tuher in case of uncut tuber, the marketable tuber (>5g) production per plant increased from 83.8 to 141.8 g/plant and the marketable tuber (>5g) production per plant of cut tuber was slightly higher than that of uncut treatment. Total tuber yield ranged from 4.16 to $6.56kg/m^2$ and the percentage of seed tubers was greater than $97\%$ for all treatments. These results indicate that seed tuber should be cut to produce large tuber $(\geq10g)$ in the recirculating wick hydroponic system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.3
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• pp.127-138
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• 2016

Diesel vehicles should be equipped with urea-selective catalytic reduction(SCR) system as a high-performance catalyst, in order to reduce harmful nitrogen oxide emissions. In this study, a three-dimensional Eulerian-Lagrangian CFD analysis was used to numerically predict the multiphase flow characteristics of the urea-SCR system, coupled with the chemical reactions of the system's transport phenomena. Then, the numerical spray structure was modified by comparing the results with the measured values from spray visualization, such as the injection velocity, penentration length, spray radius, and sauter mean diameter. In addition, the analysis results were verified by comparison with the removal efficiency of the nitrogen oxide emissions during engine and chassis tests, resulting in accuracy of the relative error of less than 5%. Finally, a verified CFD analysis was used to calculate the interanl flow of the urea-SCR system, thereby analyzing the characteristics of pressure drop and velocity increase, and predicting the uniformity index and overdistribution positions of ammonia.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.2
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• pp.85-94
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• 2004

Experimental study on combustion characteristics of double swirl coaxial injectors has been conducted for the assessment of critical injector design parameters. A reusable, unielement thrust chamber has been fabricated with a water-cooled copper nozzle. Two principal design parameters. a swirl angle and a recess length, have been investigated through hot firing tests for the understanding of their effects on high pressure combustion. Clearly, both parameters considerably affect the combustion efficiency, dynamics and hydraulic characteristics of an injector. Internal mixing of propellants in a recess region increases combustion efficiency along with the increase of a pressure drop required for flowing the same amount of mass flow rates. It is concluded that pressure buildup due to flame can be released by the increase of LOx flow axial momentum or the reduction of a recess length. Dynamic pressure measurements of the thrust chamber show varied dynamic behaviors depending on injector configurations.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.155-158
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• 2005

The spray characteristics of liquid jet minted in subsonic cross-flow were investigated numerically and experimentally. The behaviors of column, penetration and breakup of plain liquid jet in non-swirling cross-flow of air have been studied. Numerical and physical models are based on a modified KIVAII code. The primary atomization is represented by a wave model based on the KH(Kelvin-Helmholtz) instability that is generated by a high interface relative velocity between the liquid and gas flows. CCD camera has been utilized in oder to capture the spray trajectory. The nozzle diameter was 0.5 mm and its L/D ratios were between 1 and 5. Numerical and experimental results indicate that the breakup point is delayed by increasing gas momentum ratio, the penetration decreases by increasing Weber number and the turbulent or nonturbulent liquid jet is obtained at different L/D ratio.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.12
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• pp.41-47
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• 2006

A liquid rocket thrust chamber should have a high confidence in its combustion performance and combustion stability. Expecially, the injector of which function is spraying and mixing propellants plays an important role in getting the confidence. This study was carried out to evaluate combustion stability of a double swirl coaxial injector by using the model similarity method. Besides, in case of a baffle which was used to improve combustion stability, the length and gap effects of the baffle were investigated.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.3
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• pp.22-30
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• 2011

There is a many way of LPRE throttling methods, high-pressure-drop systems, dual-manifold injector, gas injection, multiple chambers, pulse modulation and movable injector components. Especially dual-manifold injector is essentially combines two fixed-area injectors into a common structure, with independent feed systems controlling flow to each injector manifold. In this paper, using indirect photography and liquid film thickness measurement with various injection pressure and tangential entry diameter to decide stability of spray over a wide thrust range in dual manifold injector.