• Journal of ILASS-Korea
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• v.4 no.3
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• pp.8-14
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• 1999

The characteristics of the breakup process in supercritical spray is investigated during the injection of supercritical sulfur hexafluoride into dissimilar gases at supercritical pressures and subcritical temperature of the injected fluid. The visualization techniques used are backlighting and shadowgraph methods. The spray angles are measured and the breakup and mixing process are observed at near and supercritical conditions. The results show that spray angles are decreased with the in..ease of the ratio of density $(\frac{\rho_f}{\rho_g})$. At the supercritical temperature, the spray angles in atomization region are kept nearly constant such as the typical spray angle in gas injection. The mixing process is changed radically at the temperature where $\frac{d\rho}{dT}=\frac{1}{2}[\frac{d\rho}{dT}]_{max}$ at given pressure.

• Journal of ILASS-Korea
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• v.4 no.4
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• pp.30-37
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• 1999

The breakup characteristics of liquid sheet formed by the liquid rocket injector has a close relation with the combustion efficiency. In this paper, basic characteristics of droplet size and velocity distribution were measured with PDPA for the Like Doublet Impinging Injector. Test variables were the angle of impact, the diameter of orifice and jet velocity. Water was used as test fluid. As a result, for impingement angle less than 90 degree, following correlations were obtained between drop size and design parameters : $D_{32}({\mu}m)=295.0{\times}V^{-0.09}\times(2\theta)^{-0.1}{\times}d^{0.072}$. For impingement angle greater than 100 degree, drop sizes were increased but eventually converged to a certain limiting value.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.5
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• pp.659-669
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• 1997

The effects of exhaust gas recirculation on diesel engine combustion and soot/NOx emissions are numerically studied. The primary and secondary atomization is modelled using the wave instability breakup model. Autoignition of a diesel spray is modelled using the Shell ignition model. Soot formation is kinetically controlled and soot oxidation is represented by a model which account for surface chemistry. The NOx formation is based on the extended Zeldovich NOx model. Effects of injection timing and concentration of $O_{2}$ and CO$_{2}$ on the pollutant formation and the combustion process are discussed in detail.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.4
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• pp.344-350
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• 2006

The present study investigates the characteristics of fire-driven heat flows and gas concentration in a compartment fire by using the modified VHS model (MVHS). The main idea of this model is to add some source terms for combustion products and oxygen consumption to the original VHS model for providing more accurate and useful information on gas concentration distributions as well as thermal fields. It is found that the present MVHS model shows fairly good agreement with the experimental data and the eddy breakup combustion model. The tilting angle of fire plume calculated by MVHS is larger than that of EBU model because the fire source of VHS is affected by ventilating flow less than EBU. However, this discrepancy is apparently reduced in the downstream region of fire source.

• Journal of ILASS-Korea
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• v.24 no.3
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• pp.145-151
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• 2019

Viscoelastic fluid is used in various industrial sites because its cost reduction and environmental benefits by preventing formation of fine droplets that scattered around. However, viscoelastic fluids, unlike newtonian fluids, contain a shear thinning characteristic that decrease in viscosity as shear rate increases and elastic characteristic, making it difficult to predict spray breakup process. In this study we made three test fluids. Boger fluid with viscoelastic characteristics, and two newtonian fluids, were prepared to exclude shear thinning characteristics and study the effects of elastic characteristic only. Flow visualization, spray angle, and SMD were measured for three test fluids using laboratory scale impinging jet test apparatus. As a result, it was confirmed that Boger fluid, unlike the newtonian fluid, was not formed fine droplets that scattered around and the breakup process appeared differently. In addition, SMD was found to be large in Boger fluid, and the SMD according to pressure was confirmed that there is no significant difference.

• Journal of ILASS-Korea
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• v.27 no.3
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• pp.144-154
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• 2022

Gas injection is a technique applied to improve throttling in liquid rocket engines and atomization in effervescent injectors. When a gas is injected into a liquid, it creates a two-phase flow inside the injector. The changes (bubbly flow, slug flow, annular flow, etc.) in the two-phase flow affect the injector's spray characteristics. In this study, cold-flow tests were performed by using three injectors with different orifice diameters and four aerators with different gas injection hole diameters. The experiments were done by changing the thrust ratio (liquid mass flow rate ratio) and gas-liquid mass flow rate ratio. Two-phase flow transition, breakup length, and discharge coefficient according to the injector/aerator design and flow conditions were investigated in detail.

• Proceedings of the Korean Society of Rheology Conference
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• 2002.05a
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• pp.117-120
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• 2002

• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.339-339
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• 2015

• 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.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.1
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• pp.28-39
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• 2003

Effects of the orifice internal flow such as cavitation and hydraulic flip on transverse injection into subsonic crossflows have been studied. The liquid column breakup length and the liquid column trajectory were measured by changing the orifice diameter (d), the orifice length/orifice diameter (L/d), the injection pressure and the shapes (sharp and round) of orifice entrance, and were compared with previous results. It is found that cavitation bubbles, which occur inside the sharp-edged orifice, make the liquid jet very turbulent and especially in the orifices with L/d ＝ 5 hydraulic flip appear as cavitation bubbles are emitted from the orifice. The breakup length is shorter as cavitation bubbles grows and hydraulic flip appears. However, the liquid column trajectories normalized by the effective diameter and the effective momentum ratio have a similar tendency irrespective of cavitation and hydraulic flip.