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CH<sub>4</sub>비예혼합화염의 수치계산에 적용하기 위한 확장된 축소반응기구의 비정상 응답특성 검토
오창보,박정,이창언,Oh, Chang-Bo,Park, Jeong,Lee, Chang-Eon 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.2
The extinction behavior and the unsteady response of augmented reduced mechanism(ARM) have been investigated by adopting an OPPDIF code and a numerical solver for the flamelet equations. By comparing the performance of the ARM based on Miller and Bowman's mechanism(MB-ARM) with that of the ARM based on GRI-Mech 3.0(GRI-3.0-ARM), it is identified that the MB-ARM is more suitable for the unsteady calculation because it is relatively less stiff than GRI-3.0-ARM during an ignition process. The steady results using the MB-ARM, which is modified to predict reasonably the extinction point of experiment, are in excellent agreement with those from full mechanism. Under the sinusoidal transient disturbances of scalar dissipation rate, the unsteady responses of the flame temperature and species concentrations using a modified MB-ARM show in very close agreement with those from full mechanism. It is presumed that above modified MB-ARM is very suitable for the unsteady simulation of turbulent flames because it gives not only a low computational cost but also a good prediction performance for flame structure, extinction point and unsteady response.
CH$_{4}$-공기 분류 확산화염의 NOx 생성특성에 관한 수치해석
오창보,이창언,O, Chang-Bo,Lee, Chang-Eon 대한기계학회 1998 大韓機械學會論文集B Vol.22 No.2
Numerical analysis was performed with multicomponent transport properties and detailed reaction mechanisms for axisymmetric 2-D CH$_{4}$ jet diffusion flame. Calculations were carried out twice with the $C_{2}$-Thermal Mechanism including $C_{2}$ and thermal NO reactions and the $C_{2}$-Full Mechanism including prompt NO reactions in addition to the above $C_{2}$-Thermal NO mechanism. The results show that the flame structures such as flame temperature, major and minor species concentration are indifferent to respective mechanisms. The production path of Thermal NO is dominant comparing with that of Prompt NO in total NO production of pure CH$_{4}$ jet diffusion flame. This is because thermal NO mechanism mainly contributes to positive formation of NO in the whole flame region, but Prompt NO mechanism contributes to negative formation in the fuel rich region. In addition, 0$_{2}$ penetration near the nozzle outlet affects the flame structures, especially N0$_{2}$ formation characteristics.
오창보,이창언,Oh, Chang-Bo,Lee, Chang-Eon 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.10
A two-dimensional direct numerical simulation was performed to investigate the flame structure of CH$_4$$N_2$-air counterflow nonpremixed flame interacting with a single vortex. The detailed transport properties and a modified 16-step augmented reduced mechanism based on Miller and Bowman's detailed chemistry were adopted in this simulation. The characteristic vortex and chemical time scales were introduced to quantify and investigate the extinction phenomenon during a flame-vortex interaction. The results showed that fuel- and air-side vortex cause an unsteady extinction. In this case, the flame interacting with a vortex was extinguished at much larger scalar dissipation rate than steady flame. It was also found that the air-side vortex extinguished a flame more rapidly than the fuel-side vortex. Furthermore, it was noted that the degree of unsteady effect experienced by a flame can be investigated by comparing the above two characteristic time scales, and this analysis could give an appropriate reason for the results of the previously reported experiment.
오창보(Chang Bo Oh),최병일(Byung-il Choi),한용식(Yong-Shik Han),김명배(Myung-Bae Kim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Unsteady simulations were performed to investigate the flame structure and the dynamic behavior of a premixed flame exposed to the wall heat loss. A 3-step global reaction mechanism was adopted in this study. Simulations were performed for two tube combustors with inner diameters(d<SUB>i</SUB>) of 1mm and 4mm. The material of tube combustor was assumed to be a Silicon Nitride(Si₃N₄). The heat loss from the outer tube wall was controlled by adjusting the amount of convective and radiative heat loss. A conical premixed flame could be stabilized inside a tube of d<SUB>i</SUB>=4㎜. The flame stability inside a tube of d<SUB>i</SUB>=4㎜ combustor was not much sensitive to the amount of heat loss. In case of a tube of d<SUB>i</SUB>=1㎜, an oscillating flame was observed in very low heat loss condition and a flame could not be sustained in realistic heat loss condition.
부력을 받는 대향류 비예혼합화염 구조에 대한 2 차원 수치모사
오창보(Chang Bo Oh),최병일(Byung-il Choi),한용식(Yong Shik Han),김명배(Myung Bae Kim),박정(Jeong Park) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
Flame structure of methane-air counterflow nonpremixed flames in buoyant field was studied numerically. A time-dependent axisymmetric two-dimensional model considering the buoyancy effects was developed to capture the flame structure. A 3-step global reaction mechanism, whose reaction coefficients were adjusted to predict the experimentally obtained extinction limits and flame temperature reasonably, was used in the simulation. The 2D simulation code was validated by comparing the flame shapes, temperature profile and extinction limits with experiment and 1D simulation results. The comparison of the flame structures between at the axisymmetric centerline and at the outer flame edge showed that the counterflow flame structures, such as temperature, fuel and oxidizer distributions, could be affected by multi-dimensional flame shape in case that a small-diameter burner was used.