• Proceedings of the KSME Conference
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• 2000.04b
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• pp.447-452
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• 2000

The low-emission and high-performance diesel combustion is an important issue in the combustion research community. In order to understand the detailed diesel flame field involving the complex Physical Processes, It Is quite desirable to study diesel spray dynamics, auto-ignition and spray flame propagation. Dynamics of fuel spray is a crucial element for air-fuel mixture formation flame stabilization and pollutant formation. In the present study, the diesel RCM (Rapid Compression Machine) and the Electric Control injection system have been designed and developed to investigate the effects of injection Pressure, injection timing, and intake air temperature on spray dynamics and diesel combustion processes. In terms of the macroscopic spray combustion characteristics it is observed that the fuel jet atomization and the droplet breakup processes become much faster by increasing the injection pressure and the spray angle. With increasing the cylinder pressure there is a tendency that the shape of spray pattern in the downstream region tends to be spherical due to the increase of air density and the corresponding drag force. Effects of intake temperature and injection pressure on auto-ignition is experimently analysed and discussed in detail.

• Journal of the Korean Society of Safety
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• v.19 no.3 s.67
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• pp.124-129
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• 2004

To evaluate the numerical method in simulation of diffusion flames and to see the effects of strain rate and fuel concentration on the flame radius and thickness, the nonpremixed methane-air counterflow flames in microgravity were simulated axisymmetrically by using the MST Fire Dynamics Simulator (FDS). The $1000^{\circ}C$ based flame radius and thickness were investigated for the mole fraction of methane in the fuel stream, $X_m=20,\;50,\;and\;80\%$ and the global strain rates $a_g=20,\;60,\;and\;90s^{-1}$ for each mole fraction. The flame radius increased with the global strain rate while the flame thickness decreased linearly as the global strain rate increased. The flame radius decreased as the mole fraction increased, but it was not so sensitive to the mole fraction compared with the global strain rate. Since there was good agreement in the nondimensional flame thickness obtained with OPPDIF and FDS respectively, it was confirmed that FDS is capable of predicting well the counterflow flames in a wide range of strain rate and fuel concentration.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.8
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• pp.997-1009
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• 1999

Silica particle formation and growth process including chemical reaction, coagulation and sintering was studied in a counterflow diffusion flame burner. The counterflow geometry provides a one dimensional flow field, along the stagnation point streamline, which greatly simplifies interpretation of the particle growth characteristics. $SiCl_4$ has been used as the source of silicon in hydrogen/oxygen/argon flames. The temperature profiles obtained by calculation showed a good agreement with experiment data. Using one and two dimensional sectional method, aerosol dynamics equation in a flame was solved, and these two results were compared. The two dimensional section method can consider sintering effect and growth of primary particle during synthesis, thus it showed evolution of morphology of non-spherical particles (aggregates) using surface fractal dimension. The effects of flame temperature and chemical loading on particle dynamics were studied. Geometric mean diameter based on surface area and total number concentration followed the trend of experiment results, especially, the change of diameters showed the sintering effect in high temperature environment.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.3
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• pp.171-176
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• 2016

Growing concerns about air pollution have led to increased demand for liquefied natural gas (LNG)-fuelled ships that have crankcases equipped with explosion relief valves to relieve excessive crankcase pressures and stop the flames emitted from the crankcase. The results of a computational fluid dynamics (CFD)-based feasibility analysis of the crankcase relief valve flame arrester design conducted using ANSYS CFX V14 showed that the inlet and outlet relief valve temperatures differed by $350-700^{\circ}C$. An explosion test was performed based on European standard EN14797 to evaluate the flame transmission and mechanical integrity of the valve. No flame transmission from the pressure vessel to the exterior was detected, and the mechanical integrity of the valve was confirmed. Thus, the relief valve components were found to be safe from the viewpoint of fracture.

• Journal of the Korea Safety Management & Science
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• v.19 no.1
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• pp.9-13
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• 2017

In this study, the height of the flame required to estimate the heat flow path and flame spread in pool fire has been applied by the empirical formula, but it is calculated without applying the pressure and temperature parameters of the fire room. Until now, the height of the flame applied to pool fire was $l_F=0.235Q^{2/5}-1.02D$ in the Heskestad empirical formula, but accurate temperature calculation was not possible due to the temperature and pressure which are not influenced by the flame height. Therefore, applying the temperature and pressure around it can calculate the exact flame height, which can be applied to fire investigation and fire dynamics. The structure of the flame is divided into a continuous flame, an intermittent flame, and a buoyancy flame, but it is assumed that the flame height is calculated from the visual aspect to the intermittent flame region, and the temperature of the buoyancy flame is very low. The effect of heat of vaporization on the height of flame was investigated. The results showed that flame height was different according to the pressure and temperature around the fire room.

• International Journal of Safety
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• v.2 no.1
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• pp.12-16
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• 2003

In Part 1, the flame structure of the counterflow nonpremixed flames computed by using Fire Dynamics Simulator was compared with that of OPPDIF for different concentrations of methane in the fuel stream. In this study, comparisons were made for the global strain rate that is an important parameter for diffusion flames for further evaluation of FDS. At each of the three fuel concentrations, $20% CH_4＋ 80% N_2, 50% CH_4 ＋ 50% N_2, 90% CH_4 ＋ 10% N_2$ in the fuel stream, the temperature and axial velocity profiles were investigated for the global strain rate in the range from 20 to $100s^{-1}$. Changes in flame thickness and radius were also compared with OPPDIF. There was good agreement in the temperature and axial velocity profiles between the axisymmetric simulations and the one-dimensional computations except for the regions where the flame temperature reach its peak and the axial velocity rapidly changes. The simulations of the axisymmetric flames with FDS showed that the flame thickness decreases and the flame radius increases with increasing global strain rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.9
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• pp.1185-1191
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• 1999

Radiation-induced oscillatory instability in diffusion flames is numerically investigated with nonlinear dynamics considered. As the simplest flame model, a diffusion flame established in the stagnant mixing layer is employed with optically thin gas-phase radiation and unity Lewis numbers for all species. Attention is focused on the radiation-induced extinction regime, which occurs at large $Damk\ddot{o}hler$ number. Once the steady flame structure is obtained for a prescribed value of the initial $Damk\ddot{o}hler$ number, transient solution of the flame is calculated after a finite amount of the $Damk\ddot{o}hler$-number perturbation is imposed on the steady flame. Transient evolution of the flame exhibits three types of flame-evolution behaviors, namely decaying oscillatory solution, diverging solution to extinction and stable limit-cycle solution. A dynamic extinction boundary is identified for laminar flamelet library.

• International Journal of Safety
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• v.2 no.1
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• pp.7-11
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• 2003

Structure of the counterflow nonpremixed flames were investigated by using Fire Dynamics Simulator(FDS) and OPPDIF to evaluate FDS for simulations of the diffusion flame. FDS, employed a mixture fraction formulation, were applied to the diluted axisymmetric methane-air nonpremixed counterflow flames. Fuel concentration in the mixture of methane and nitrogen was considered as a numerical parameter in the range from 20% to 100% increasing by 10% by volume at the global strain rates of $a_g = 20S^{-l} and 80S^{-1}$ respectively. In all the computations, the gravity was set to zero since OPPDIF is not able to compute the buoyancy effects. It was shown by the axisymmetric simulation of the flames with FDS that increasing fuel concentration increases the flame thickness and decreases the flame radius. The centerline temperature and axial velocity, and the peek flame temperature showed good agreement between the both methods.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.12
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• pp.1669-1680
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• 1998

A method is developed to include the effect of volume expansion in the description of the flame dynamics using G-equation. Line volume-source is used to represent the effect of the exothermic process of combustion with source strength assigned by the density difference between the burned and the unburned region. The present model provides good agreement with the experimental results. Including volume expansion, the flow field is adjusted to accommodate the increased volume flow rate which crossing the flame front and the result predicts the same behavior of measured velocity field qualitatively. The effect of increasing volume expansion does not change the initial growth rate of flame area but increase the residence time. Consequently this effect increases the maximum area of flame front. The flame propagation in varying flow field due to volume expansion provides a promising way to represent the wrinkled turbulent premixed flames in a numerically efficient manner.

• Fire Science and Engineering
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• v.32 no.3
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• pp.42-50
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• 2018

The effect of sub-grid turbulence and combustion models on the mean flame height in a heptane pool fire according to the Fire Dynamics Simulator (FDS) version (5 and 6) based on Large Eddy Simulation (LES) was examined. The heat release rate for the fire simulation was provided through experiments performed under identical conditions and the predictive performance of the mean flame height according to FDS version was evaluated by a comparison with the existing correlation. As a result, the Smagorinsky and Deardorff turbulence models applied to FDS 5 and 6, respectively, had no significant effects on the mean flow field, flame shape and flame height. On the other hand, the difference in pool fire characteristics including the mean flame height was due mainly to the difference in the mixture fraction and Eddy Dissipation Concept (EDC) combustion models applied to FDS 5 and 6, respectively. Finally, compared to FDS 6, FDS 5 provided the predictive result of a significantly longer flame height and more consistent mean flame height than the existing correlation.