• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.14 no.6
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• pp.58-68
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• 2000

In this paper, a mathematical model of describing oxygen density in multi-band type reheating furnaces was presented. Model designed in this paper was composed of majorly two parts. One is a model regarding 'variation of existing gas'. The other is a model of showing 'variation of oxygen content'. Each model is designed by considering four factors related to variation of oxygen density based on chemical reaction, fluid dynamics and fuzzy theory. Four factors to be considered are combustion reaction in burner, fluid transfer between adjacent combustion bands, fluid transfer from furnace's inner space to external space, and input of external air via gates. According to simulation results, it was shown that varying pattern of oxygen density in each combustion band is similar to generally expected operation data in reheating furnace.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.10
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• pp.1368-1379
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• 2000

A numerical study on swirling pulverized coal combustion in an axisymmetric enclosure is carried out by applying the 2-phase weighted sum of gray gases model (WSGGM) approach with the discrete ordinate method (DOM) to model the radiative heat transfer equation. In the radiative transfer equation, the same polynomial equation and coefficients for weighting factors as those for gas are adopted for the coal/char particles as a function of partial pressure and particle temperature. The Eulerian balance equations for mass, momentum, energy, and species mass fractions are adopted with the standard and RNG k-${\varepsilon}$ turbulence model, whereas the Lagrangian approach is used for the particulate phase. The eddy-dissipation model is employed for the reaction rate for gaseous mixture, and the single-step and two-step first-order reaction model for the devolatilization process for coal. Special attention is given to establish the thermal boundary conditions on radiative transfer equation By comparing the numerical results with experimental ones, the radiation model used here is confirmed and found to provide an alternative for simulating the radiative transfer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.10
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• pp.1363-1370
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• 1997

Single liquid droplet combustion processes including heating, evaporation, droplet burning and flame radiation were theoretically investigated by adopting nongray gas radiation model for the radiative transfer equation (RTE). n-Heptane was chosen as a fuel and the numerical results were compared with the experimental data available in the literature. The discrete ordinate method (DOM) was employed to solve the radiative transfer equation and the weighted sum of gray gases model (WSGGM) was applied to account for nongray effect by CO$_{2}$, and H$_{2}$0. Therefore, detailed effects by nongray gas and its comparison with the gray gas model could be figured out in the results. It is found that the radiative heat flux is higher when the nongray model is used, thereby reducing the maximum gas temperature and the flame thickness, but the total burning time increases due to the deceased conductive heat flux in nongray model. Consequently, a better agreement with experimental data could be obtained by using nongray model.

• 한국연소학회:학술대회논문집
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• 2004.11a
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• pp.197-205
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• 2004

Most of gas turbines is operated by the type of dry premixed combustion to reduce NOx emission and economize fuel consumption. However this type operation, combustion induced instability brought failure problems cause by high pressure and heat release fluctuations. Though there has been lots of studies since Lord Rayleigh to understand this instability mechanism and control the instabilities, none of them made matters clear. In order to understand the instability phenomena, a simple experimental study with dump combustor was conducted at the moderate pressure and ambient temperature conditions. From this model gas turbine combustor self-excited instabilities at the resonance mode(200Hz) and bulk mode(10Hz) were occurred and observed at the three points of view; pressure, heat release and equivalence ratio which are acquired by peizo-electric transducer, HICCD camera and acetone LIF respectively. From this results we could see the instability mechanism clear with the account of time scale analysis which explained by the propagation of pressure wave to the upward of mixture stream and convectional transfer of the equivalence ratio fluctuation by this pressure fluctuation.

• Transactions of the Korean hydrogen and new energy society
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• v.31 no.1
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• pp.96-104
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• 2020

A model combustor has been designed and fabricated for studying the combustion characteristics of oxygen (O₂)/hydrogen (H₂) flames under supercritical conditions. The combustor is designed to allow combustion experiments up to 60 bar, the supercritical pressure condition of O₂ and H₂. Injectors can be replaced to study various types of flames and the combustion chamber is designed to visualize flames by installing optical windows. Through the preliminary tests, including a high-pressure (up to 60 bar) test using air and combustion tests for coaxial jet flames of liquid oxygen (LO₂)/gaseous hydrogen (GH₂) at elevated pressure, the reliability of the combustor has been demonstrated.

• 한국연소학회:학술대회논문집
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• 2000.12a
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• pp.83-91
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• 2000

A numerical study was carried out to investigate the 'unstart' process of thermally-choked combustion in model scramjet engines. The combustion mechanism of supersonic combustor will be compared with the experimental results obtained from the T3 free-piston shock tunnel at ANU (Australian National University) and the high enthalpy supersonic wind tunnel at UT (University of Tokyo). For the numerical simulation of supersonic combustion. multi-species Navier-Stokes equations were considered. and detailed chemistry reaction mechanism of $H_2$-Air were adopted. The governing equations were solved by Roe's FDS method and LU-SGS method with MUSCL scheme. In this study. it is found that the thermal choking process could result from excessive heat release due to combustion. In detail, sufficient heat release could be generated at local region of very high temperature increased by reflection of shock waves or vortex sheets. Accordingly the flow of downstream of the combustor fell to subsonic field propagated upstream along the combustor. Sometimes the subsonic flow field propagated into isolator could generate precombustion shock waves in the isolator.

• Journal of the Korean Society of Combustion
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• v.20 no.3
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• pp.35-42
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• 2015

Investigating coal combustion in a large-scale boiler using computational fluid dynamics (CFD) requires a combination of flow and reaction models. These models include a number of rate constants which are often difficult to determine or validate for particular coals or furnaces. Nonetheless, CFD plays an important role in developing new combustion technologies and improving the operation. In this study, the model selection and rate constants for coal devolatilization, char conversion, and turbulent reaction were evaluated for a commercial wall-firing boiler. The influence of devolatilization and char reaction models was found not significant on the overall temperature distribution and heat transfer rate. However, the difference in the flame shapes near the burners were noticeable. Compared to the coal conversion models, the rate constant used for the eddy dissipation rate of gaseous reactions had a larger influence on the temperature and heat transfer rate. Based on the operation data, a value for the rate constant was recommended.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.379-385
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• 2010

Mechanism of combustion frequencies occurring during combustion is experimentally investigated in a model combustor with V-gutter flameholder. The combustor has a long duct shape with a cross section area of $40{\times}40mm$. The v-gutter type flameholder with 10, 12, 14mm width is mounted at the side wall of combustor. CNG were used as fuel, and the fuel was injected transversely into air crossflow. It is found that combustion frequencies were considered as first longitudinal mode caused by combustor geometry. And it is found that flameholder length affects the flame holding range. Also, it is observed first longitudinal pressure oscillations make significant changes of flame structure.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.411-414
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• 2010

In supersonic propulsion system, the inlet buzz phenomenon in the subcritical operation arises large pressure oscillation, combustion instability, and thrust loss, etc. Inlet Buzz phenomenon and the spray injection/combustion are figured out by the unified unsteady numerical analysis. TAB(Taylor Analogy Breakup) model was applied. Acoustic mode of the entire engine was investigated by detail analysis of pressure fluctuation at each location of the engine.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.2
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• pp.179-185
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• 2008

Simulating combustion tests have been performed to elucidate the effect of baffle gaps on the optimal damping characteristics in liquid rocket combustors where coaxial injectors are installed. Amplitude of pressure oscillation in model combustion chamber and the combustion stability margin are used to quantify the damping capacitance of baffles. Satisfactory agreement has been achieved with the results of cold acoustic tests. Present results have shown that the optimal gap for high acoustic damping capacity has also the large combustion stability margin in simulating combustion tests. Therefore, the present results can be utilized to determine the baffle length and optimal gap in full-scaled rocket combustors.