• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.5
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• pp.695-702
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• 2002

Nonlinear dynamics of striped diffusion flames, by the diffusional-thermal instability with Lewis numbers sufficiently less than unity, is numerically investigated by examining various two-dimensional flame-structure solutions. The Lewis numbers for fuel and oxidizer are assumed to be identical and an overall single-step Arrhenius-type chemical reaction rate is employed in the model. Particular attention is focused on identifying the flame-stripe solution branches corresponding to each distinct stripe pattern and hysteresis encountered during the transition. At a Damkohler number slightly greater than the extinction Damkohler number, eight-stripe solution first emerges from one dimensional solution. The eight-stripe solution survives Damkohler numbers much smaller than the extinction Damkohler number until the transition to four-stripe solution occurs at the first forward transition Damkohler number. At the second forward transition Damkohler number, somewhat smaller than the first transition Damkohler number, the transition to two-stripe solution occurs. However, anu further transition from two-stripe solution to one-stripe solution is not always possible even if one-stripe solution can be independently accessed for particular initial conditions. The Damkohler number ranges for two-stripe and one-stripe solutions are found to be virtually identical because each stripe is an independent structure if distance between stripes is sufficiently large. By increasing the Damkohler number, the backward transition can be observed. In comparison with the forward transition Damkohler numbers, the corresponding backward transition Damkohler numbers are always much greater, thereby indicating significant hysteresis between the stripe patterns of strained diffusion flames.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.197-201
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• 2009

Experiments were conducted to study the transition of shrinking flame disk to flame hole in counterflow diffusion flames. The studies of transition are well described by varying burner diameters, global strain rate and velocity ratio. It is experimentally verified that radial conduction heat loss is affected at even high strain rate flames for appropriately small burner diameters. It is also shown that flame extinction modes are grouped into three and particularly, hole or stripe is observed in sufficiently high strain rate flames. There exists critical radius according to burner diameter which divide flame extinction modes into three parts.