• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.6
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• pp.625-632
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• 2011

The ignition characteristics of a $CH_4$/hot air counterflow diffusion flame were investigated numerically using a flame-controlling continuation method. For the chemical reactions, the GRI-v1.2 reaction mechanism was used in the simulation. The maximum flame temperature was presented in the space of the inverse global strain rate, and showed S-curve-type behavior. The flame temperatures and velocities of the upper and middle branches were compared for different global strain rates. In addition, the global strain rate was compared with the local strain rates defined at the flame surface and the boundaries of the fuel and oxidizer sides of the fuel/air mixing layer. These local strain rates correlated well with the global strain rate.

• Proceedings of the KAIS Fall Conference
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• 2002.11a
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• pp.293-296
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• 2002

본 논문에서는 수소/액체연료/공기의 연소특성에 대해 CFD상용프로그램을 사용하여 수치해석을 수행하였다. 먼저 프로그램을 검증하기 위하여 수소/공기의 난류 비예혼합 화염에 대한 반응물과 생성물의 몰분율을 Barlow실험 결과와 비교하였고, X축 방향의 온도분포를 Flury의 실험 값과 비교하여 값이 물리적으로 근사함을 확인하였다. 혼합분율(Mixture Fraction)과 확률밀도함수(PDF)의 접근 방법을 이용하여 화염진단과 오염물질발생에 중요한 역할을 하는 중간 종들의 몰분율을 확인하였다. 수소/액체연료/공기에 대해서는 화염형성에 있어서 가장 중요한 연료와 산화제의 속도비 변화(100,10,1,0.1)로부터 산화제속도가 연료속도 보다 클 경우 고속 측인 산화제에 의해 연료의 확산이 지배되는 현상으로 인하여 화염의 온도분포가 최고가 됨을 확인하였다. 또한, 연소과정 중 발생하는 오염물질의 농도를 수치적으로 해석하여 최저의 오염농도를 가질 수 있는 속도 비를 찾아 낼 수 있었다. 수소/공기와 수소/액체연료/공기의 온도 장 비교를 통하여 수소/액체연료/공기의 혼합물이 대체에너지로서의 가능성을 확인하였다.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.10
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• pp.1081-1089
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• 2005

In order to examine the application feasibility of Orimulsion fuel in a commercial boiler using heavy fuel oil, a numerical and experimental research efforts have been made especially to figure out the fundamental combustion characteristics of this fuel in a small-scale boiler. One of the notable combustion features of Orimulsion fuel is the delayed appearance of flame location with the flame shape of rather broad distribution, which is found experimentally and confirmed by numerical calculation. This kind of flame characteristics is considered due to the high moisture content included inherently in the process of Orimulsion manufacture together with micro-explosion by the existence of fine water droplets. In order to investigate the effect on the combustion characteristics of Orimulsion, a series of parametric investigation have been made in terms of important design and operational variables such as injected amount of fuel, types of atomization fluid, and phonemenological radiation model employed in the calculation, etc. The delayed feature of peak flame can be alleviated by the adjustment of the flow rate of injected fuel and the generating features of CO, $SO_2$ and NO gases are also evaluated in the boiler. When the steam injection as atomizing fluid is used, the combustion process is stabilized with the reduced region of high flame temperature. In general, the calculation results are physically acceptable and consistent but some refinements of phenomenological models are necessary for the better resolution of pollutant formation. From the results of this small-scale Orimulsion boiler, it is believed that a number of useful information are obtained with the working computer program for the near future application of Orimulsion fuel to a conventional boiler.

• Fire Science and Engineering
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• v.27 no.6
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• pp.50-56
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• 2013

The radiation effects on the auto-ignition and extinction characteristics of a non-premixed fuel-air counterflow field were numerically investigated. A detailed reaction mechanism of GRI-v3.0 was used for the calculation of chemical reactions and the optically-thin radiation model was adopted in the simulations. The flame-controlling continuation method was also used in the simulation to predict the auto-ignition point and extinction limits precisely. As a result, it was found that the maximum H radical concentration, $(Y_H)_{max}$, rather than the maximum temperature was suitable to understand the ignition and extinction behaviors. S-, C- and O-curves, which were well known from the previous theory, were identified by investigating the $(Y_H)_{max}$. The radiative heat loss fraction ($f_r$) and spatially-integrated heat release rate (IHRR) were introduced to grasp each extinction mechanism. It was also found that the $f_r$ was the highest at the radiative extinction limit. At the flame stretch extinction limit, the flame was extinguished due to the conductive heat loss which attributed to the high strain rate although the heat release rate was the highest. The radiation affected on the radiative extinction limit and auto-ignition point considerably, however the effect on the flame stretch extinction limit was negligible. A stable flame regime defined by the region between each extinction limit became wide with increasing the fuel temperature.

• Journal of the Korean Institute of Gas
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• v.7 no.3 s.20
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• pp.44-50
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• 2003

The axisymmetric methane-air counterflow flame was simulated to investigate changes in the flame structure due to the fuel concentration and to evaluate the numerical method. The global strain rates $a_g=20,\;60,\;90\;s^{-1}$ and the mole fractions of methane $x_m=20,\;50,\;80\%$ in the fuel stream were taken to be numerical parameters. The axisymmetric simulation was conducted by using the Fire Dynamics Simulator (FDS) which employed a mixture fraction combustion model, and the results were compared with those of OPPDIF, which is an one-dimensional flamelet code and includes detail chemical reactions. In all the cases tested, there was good agreement in the temperature and axial velocity profiles between the axisymmetric and one-dimensional simulations. It was shown that the flame thickness and peak flame temperature increase and the flame radius decreases as the fuel concentration increases.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.6
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• pp.365-371
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• 2019

In this study, the flame temperature distribution of the diffusion flame burner for SiO₂ deposition was analyzed by the computational fluid analysis. This corresponds to the previous step for simulating the SiO₂ preform deposition process for manufacturing optical fibers using environmentally friendly raw materials. In order to model premixed combustion, heat flow, convection, and chemical reactions were considered, and Reynolds-averaged Navier-Stokes equations and k-ω models were used. As a result, the temperature distribution of the flame showed a tendency to increase the distance from the nozzle surface to the maximum temperature when the flow rate of the auxiliary oxygen increased. In addition, it was confirmed that the temperature distribution due to incomplete combustion was large in the combustion reaction with a large equivalence ratio of the mixed gas.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.2
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• pp.55-64
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• 2015

In this study, a 3-D flame cooling analysis is conducted to examine thermal safety for the flame deflector of the 75 tonf class propulsion test facility, and the safe discharge of the exhaust gas is assessed by using numerical results. The Mixture multiphase model is adopted for the simulation of heat transfer and phase exchange process between flame and cooling water, and the computational study using the single species unreacted model for the exhaust plume is carried out for the flame cooling. Numerical analysis predicts maximum temperature on the flame deflector wall for different water flow rates, and evaluates the safe minimum flow rate of water corresponding to the fire-resistant temperature for concrete.

• Fire Science and Engineering
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• v.17 no.3
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• pp.20-25
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• 2003

Measurements with filaments and thermocouples and computations with Oppdif and FDS were carried out to investigate the impact of flame strain, agent addition, and buoyancy on the structure and extinction of nonpremixed counterflow flames. Measurements through 2.2 s drop tests in microgravity conditions and experiments in normal gravity conditions were compared with the results of computations. For the global strain rates 7 s$^{-1}$ through 100 s$^{-1}$ , the turning point behavior in the critical nitrogen concentration at O-g was confirmed. The effects of buoyancy, that is, changes in the flame curvature and thickness were also confirmed by the computations with FDS. There was agreement in the peak flame temperature and its position between the computations and the measurements in the near extinction methane/air diffusion flames in microgravity.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.3370-3375
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• 2014

MILD combustion is a highly favored technology for solving the trade-off relation between high thermal efficiency and low pollutant emissions. The system has low NOx concentration in high temperature combustion by recirculating the combustion gas, as well as improving the thermal efficiency by making the internal temperature in a combustion furnace uniform. This study describes the combustion characteristics of a conical MILD combustor in a laboratory-scale furnace by adjusting the equivalence ratio with the fuel gas flow rate while maintaining a constant air flow rate of the furnace. The MILD regime in the furnace is well characterized and the in-furnace temperature and emissions were predicted, respectively, for the range of equivalence of 0.69 - 0.83. For the range of equivalence ratios, this study confirmed the existence of a stable flame region that has an approximately $300^{\circ}C$ temperature difference between the maximum flame temperature region and main reaction region.

• Fire Science and Engineering
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• v.27 no.5
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• pp.19-25
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• 2013

The fire took place in the synthetic heat transfer fluid boiler. This study uses simulation to investigate the first, second and third passes and the temperature in the fire burner. The boiler's internal fluid is more or less unsteady due to the out of order inverter. As the operation continues, the flame's flow and speed are unsteady. The synthetic heat transfer fluid leak spouted about 120 kg/min in the form of vapor in the early period of the fire. The flame extended to the second and third passes. The highest temperature of the second and third pass is $1059^{\circ}C$ and $1007^{\circ}C$, respectively. The simulation shows that the temperature is $767^{\circ}C$ in the low part of the third pass. The synthetic heat transfer fluid spouted through the cracked part of the fire box in the first pass and accumulated on the turn table. The temperature rises to $183^{\circ}C$ in the low part of the burner. Therefore, it is expected that the temperature of the interior of the fire box is above $1200^{\circ}C$. The temperature of the burner rises to a maximum level several times in a short period. On account of that, several explosions occur in the fire burner.