• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.3
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• pp.589-597
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• 1992

The effect of pressure on soot formation in premixed propane-air combustion is investigated at high pressures over the pressure range of 1 to 5 MPa by using a specially designed constant volume combustion bomb. The combustiom chamber of disk type with eight spark plugs located on the circumference at an interval of 45deg is 100mm in diameter by 14mm thick. The end gases are compressed to high pressures by the eight converging flames. The soot volume fraction in the chamber center during the final stage of combustion at the highest pressure is measured by the in-situ laser extinction technique, and the burnt gas temperature during the same period is measured by the two-color method. It is found that the soot yield rises with 50 to 100% for the respective equivalence ratio range of 1.9-2.2 at an interval of 0.1 when the combustion pressure is increased from 1 to 5 MPa, and that the turbulent flames decrease in the soot yield as compared with the laminar flames because the burnt gas temperatures increase with the drop of heat loss.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.9
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• pp.2339-2358
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• 1993

Since the rate and completeness of combustion in direct injection engines were controlled by the characteristics of gas flow fields and sprays, an understanding of those was essential to the design of the direct injection engines. In this study the numerical simulations of injection pressure effects on the characteristics of gas flow fields and sprays were preformed using the spray model that could predict the interactions between gas fields and spray droplets. The governing equations were discretized by the finite volume method and the modified k-.epsilon. model which included the compressibility effects due to the compression/expansion of piston was used. The results of the numerical calculation of the spray characteristics in the quiescent environment were compared with the experimental data. There were good agreements between the results of calculation and the experimental data, except in the early stages of the spray. In the motoring condition, the results showed that a substantial air entrainment into the spray volume was emerged and hence the squish motion was relatively unimportant during the fuel injection periods. It was found that as the injection pressure increased, the evaporation rate of droplets was decreased due to the narrow width of spray and the increased number of droplets impinged on the bottom of the piston bowl.

• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2616-2628
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• 2021

The results of effective irradiation swelling in a wide range of burnup levels are numerically obtained for an inert matrix fuel, which are verified with DART model. The fission gas swelling of fuel particles is calculated with a mechanistic model, which depends on the external hydrostatic pressure. Additionally, irradiation and thermal creep effects are included in the inert matrix. The effects of matrix creep strains, external hydrostatic pressure and temperature on the effective irradiation swelling are investigated. The research results indicate that (1) the above effects are coupled with each other; (2) the matrix creep effects at high temperatures should be involved; and (3) ranged from 0 to 300 MPa, a remarkable dependence of external hydrostatic pressure can be found. Furthermore, an explicit multi-variable mathematic model is established for the effective irradiation swelling, as a function of particle volume fraction, temperature, external hydrostatic pressure and fuel particle fission density, which can well reproduce the finite element results. The mathematic model for the current volume fraction of fuel particles can help establish other effective performance models.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.7 s.250
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• pp.682-691
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• 2006

This study was conducted to assess the effect of mixed fuel composition and mass fraction on spray inner structure in evaporating transient spray under the various ambient conditions. Spray structure and spatial distribution of liquid phase concentration are investigated using a thin laser sheet illumination technique on the multi-component mixed fuels. A pulsed Ar+ laser was used as a light source. The experiments were conducted in a constant volume vessel with optical access. Fuel was injected into the vessel with electronically controlled common rail injector. Used fuel contain $i-octane(C_8H_{18}),\;n-dodecane(C_{12}H_{26})$ and $n-hexadecane(C_{16}H_{34})$ that are selected as low-, middle- and high-boiling point fuel, respectively. Experimental conditions are 25Mpa, 42MPa, 72MPa and 112MPa in injection pressure, $5kg/m^3,\;15kg/m^3\;and\;20kg/m^3$ in ambient gas density, 400K, 500K, 600K and 700K in ambient gas temperature, 300K and 368K in fuel temperature, and different fuel mass fraction. Experimental results indicate that the more high-boiling point component, the longer the liquid phase it were closely related to fuel physical properties, but injection pressure had no effect on. And there was a high correlation between the liquid phase length and boiling temperature at 75% distillation point.

• Progress in Superconductivity and Cryogenics
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• v.18 no.4
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• pp.9-14
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• 2016

The effect of the size and shape of magnesium(Mg) powder on the formation of $MgB_2$ and the critical current density($J_{c,}$) of $MgB_2$ bulk was studied. As a precursor for the formation of $MgB_2$, Mg and $MgB_4$ powder, which was synthesized through the reaction of boron (B) with Mg powders, was used. $MgB_4$ was mixed with Mg powders of various sizes, pressed into pellets and heat-treated at $650^{\circ}C-750^{\circ}C$ in flowing argon gas. The XRD analysis of the heat-treated $MgB_2$ samples showed that the volume fraction of $MgB_2$ was the highest as 92.74 % when spherical Mg powder with an average size of $25.7{\mu}m$ was used, whereas the volume fraction was the lowest as 79.64 % when plate-like Mg powder with a size of $34.1{\mu}m$ was used. The superconducting transition temperature ($T_c$) of $MgB_2$ was not sensitive to the characteristics of the Mg powders used. All of the prepared $MgB_2$ samples showed a high $T_c$ of 38.3 K and a small superconducting transition width of 0.2 K-0.5 K. $J_c$ (5 K and 1 T) of $MgB_2$ was the highest as $3.93{\times}10^4A/cm^2$ when spherical Mg powder with a size of $25.7{\mu}m$ was used, whereas $J_c$ was the lowest as $2.18{\times}10^4A/cm^2$when plate-like Mg powder with a size of $34.1{\mu}m$ was used. The relationship between the $J_c$ of $MgB_2$ and the characteristics of the Mg powders used was explained in terms of the volume fraction of $MgB_2$ and the apparent density of the $MgB_2$ pellets.

• Journal of Powder Materials
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• v.27 no.2
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• pp.139-145
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• 2020

The powder manufacturing process using the gas atomizer process is easy for mass production, has a fine powder particle size, and has excellent mechanical properties compared to the existing casting process, so it can be applied to various industries such as automobiles, electronic devices, aviation, and 3D printers. In this study, a modified A4032-xSn (x = 0, 1, 3, 5, and 10 wt.%) alloy with low melting point properties is investigated. After maintaining an argon (Ar) gas atmosphere, the main crucible is tilted; containing molten metal at 1,000℃ by melting the master alloy at a high frequency, and Ar gas is sprayed at 10 bar gas pressure after the molten metal inflow to the tundish crucible, which is maintained at 800℃. The manufactured powder is measured using a particle size analyzer, and FESEM is used to observe the shape and surface of the alloy powder. DSC is performed to investigate the change in shape, according to the melting point and temperature change. The microstructure of added tin (Sn) was observed by heat treatment at 575℃ for 10 min. As the content of Sn increased, the volume fraction increased to 1.1, 3.1, 6.4, and 10.9%.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2983-2988
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• 2007

In the present study, the numerical investigation on the effects of water-mist characteristics has been carried out for the fire suppression mechanism. The FDS are used to simulate the interaction of fire plume and water mists, and program describes the fire-driven flows using LES turbulence model, the mixture fraction combustion model, the finite volume method of radiation transport for a non-scattering gray gas, and conjugate heat transfer between wall and gas flow. The numerical model is consisted of a rectangular enclosure of $L{\times}W{\times}H=1.5{\times}1.5{\times}2.0m$ and a water mist nozzle that be installed 1.8m from fire pool. In the study, the parameters of nozzle for simulation are the droplet size and the spray velocity. Finally, the droplet size influences to fire flume on fire suppression than spray velocity because of the effect of terminal velocity, and the optimal condition for fire suppression is that the droplet size and the spray velocity are $100{\mu}m$ and 20m/s, respectively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.7 s.262
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• pp.596-603
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• 2007

As increasing interest for soot emission. etc in combustion systems, various studies are being carried out for the reduction and measurement techniques of soot. Especially, laser induced incandescence is the useful measurement technique which has distinguished spatial and temporal resolution for primary particle size, volume fraction and aggregated particle size etc. Time resolved laser induced incandescence is the technique for measuring primary particle size that is decided to solve the signal decay rate which is related to the cooling behavior of heated particle by pulsed laser. The cooling behavior of heated particle is able to represent the heat and mass transfer model which are involved constants of soot property for surround gas temperature on the our previous work. In this study, it is applied to the time-dependence thermodynamic properties for soot temperature instead of constants of soot property for surround gas temperature and compared two different model results.

• Journal of Power System Engineering
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• v.13 no.5
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• pp.25-33
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• 2009

In the present study, the numerical investigation has been carried out to see the effects of water mist sprays on the fire suppression mechanism. The special-purposed program named as FDS was used to simulate the interaction of fire plume and water mists. This program solves the fire-driven flows using LES turbulence model, the mixture fraction combustion model, the finite volume method of radiation transport for a non-scattering gray gas, and conjugate heat transfer between wall and gas flow. The computational domain was composed of a rectangular space dimensioned as $L{\times}W{\times}H=4.0{\times}4.0{\times}2.5\;m^3$ with a mist-injecting nozzle installed 1.0 m high from the fire pool. In this paper, two types of nozzles were chosen to compare the performance of the fire suppression. Numerical results showed that the nozzle, type A, with more orifices having smaller diameters had poorer performance than the other one, type B because the flow injected through side holes deteriorated the primary flow. The fire-extinguishing time of type A was 2.6 times bigger than that of type B.

• Journal of ILASS-Korea
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• v.22 no.4
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• pp.175-184
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• 2017

The numerical investigation on the effects of water-mist characteristics has been carried out for the fire suppression mechanism. The FDS are used to simulate the interaction of fire plume and water mists, and program describes the fire-driven flows using LES turbulence model, the mixture fraction combustion model, the finite volume method of radiation transport for a non-scattering gray gas, and conjugate heat transfer between wall and gas flow. The numerical model is consisted of a rectangular enclosure of $L{\times}W{\times}H=1.5{\times}1.5{\times}2.0m^3$ and a water mist nozzle that be installed 1.8 m from fire pool. In the present study, the parameters of nozzle for simulation are the droplet size and the spray velocity. The droplet size influences to fire flume on fire suppression more than the spray velocity because of the effect of the terminal velocity. The optimal condition for fire suppression is that the droplet size and the spray velocity are $100{\mu}m$ and 20 m/s respectively.