• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.247-250
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• 2015

The characteristics of opposed nonpremixed tubular flames with radiation heat loss are investigated using linear stability analysis and 2-D numerical simulations. Two extinction limits, as the $Damk{\ddot{o}}hler$ number is small or large, are confirmed using finite difference method with a simple continuation method. It is verified that the results of linear stability analysis predict the number of flame cells and the critical Da starting cellular instability or amplification of temperature near both extinction limits with good resolution.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.46-49
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• 2006

Extinction limits and combustion temperatures in heat-recirculating excess enthalpy reactors employing both gas-phase and catalytic reaction have been examined previously, with and emphasis Reynolds number (Re) effects and possible application to microscale combustion devices. However, Re is not the only parameter needed to characterize reactor operation. In particular, the use of a fixed reactor size implies that residence time and Re cannot be adjusted independently. To remedy this situation, in this work geometrically similar reactors of different physical sizes were tested with the aim of independently determining the effects of Re and Da. It is found that the difference between catalytic and non-catalytic combustion limits narrow as scale decreases. Moreover, to assess the importance of wall thermal conductivity, reactors of varying wall thickness were studied. From these results the effect of scale on microscale reactor performance and implications for practical microcombustion devices are discussed.

• Journal of the Korean Society of Combustion
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• v.6 no.1
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• pp.7-13
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• 2001

Propagation characteristics of tribrachial flames have been studied numerically in a two-dimensional fuel/oxidizer mixing layer. A flame is initiated by imposing a high temperature ignition source. Subsequent propagation of a tribrachial flame is traced. The flow redirection effect at the leading edge of a tribrachial flame increases the propagation speed beyond the corresponding stoichiometric laminar burning velocity. The effect of mixture fraction gradient on the propagation speed of a tribrachial flame is analyzed in a mixing layer considering that mixture fraction gradient increases as a tribrachial flame propagates toward upstream. As the flame curvature at the leading edge increases with decreasing mixture fraction gradient, the flow redirection effect becomes more pronounced on the flame propagation speed. As a result, the propagation speed of a tribrachial flame increases with decreasing mixture fraction gradient.

• Journal of the Korean Society of Combustion
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• v.20 no.1
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• pp.43-51
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• 2015

A study on laminar jet flames in coflow air diluted with helium has been conducted to investigate self-excitations for various propane mole fractions and nozzle exit velocities. The stability map was represented as a function of nozzle exit velocity and fuel mole fraction for propane. The results show that two types of self-excitation were observed : (1) buoyancy-driven self-excitation (hereafter called BDSE) and (2) Lewis-number induced-self-excitation coupled with (1) (hereafter called LCB) near extinction limit for 9.4 mm nozzle diameter. It was shown that with 0.95 mm nozzle diameter, Lewis-number-induced self-excitation (hereafter LISE) and BDSE could be separated. The differences between the two self-excitations were shown and discussed.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.1
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• pp.11-18
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• 2011

The geometrically similar swiss roll reactors of different physical sizes were tested with the aim of independently determining the effects of Re and Da. It is found that the difference between catalytic and non-catalytic combustions extinction limits are narrowed as scale decreases. In addition to assess the importance of fuel chemistry, different families of fuels including alkanes and ethers were tested. From these results the effect of scale and fuel type on microscale reactor performance and implications for practical micro combustion devices are discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.857-864
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• 2012

A linear stability analysis of a diffusion flame with radiation heat loss is performed to identify linearly unstable conditions for the Damk$\ddot{o}$hler number and radiation intensity. We adopt a counterflow diffusion flame with unity Lewis number as a model. Near the kinetic limit extinction regime, the growth rates of disturbances always have real eigenvalues, and a neutral stability condition perfectly falls into the quasi-steady extinction. However, near the radiative limit extinction regime, the eigenvalues are complex, which implies pulsating instability. A stable limit cycle occurs when the temperatures of the pulsating flame exceed the maximum temperature of the steady-state flame with real positive eigenvalues. If the instantaneous temperature of the pulsating flame is below the maximum temperature, the flame cannot recover and goes to extinction. The neutral stability curve of the radiation-induced instability is plotted over a broad range of radiation intensities.