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TECHNICAL BRIEFS

Correlations for the Onset of Instabilities of Spherical Laminar Premixed Flames

[+] Author and Article Information
M. Z. Haq

Department of Mechanical Engineering, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladeshzahurul@me.buet.ac.bd

J. Heat Transfer 127(12), 1410-1415 (Jan 25, 2005) (6 pages) doi:10.1115/1.2098867 History: Received April 01, 2004; Revised January 25, 2005

A spherically expanding flame in a quiescent premixture is a bifurcation phenomenon, in which the flame becomes unstable at a radius, greater than some critical value, while remaining stable below that critical radius. Beyond this critical radius, developing instabilities are initiated by propagating cracks to form a coherent structure covering the entire flame surface and the flame accelerates. The present paper reports a Schlieren photographic study of spherical flame propagation in methane—air, iso-octane—air and n-heptane—air premixtures at different initial conditions where the onset of instability and the flame acceleration are clearly perceived. Critical size and corresponding elapsed time for the development of such instability are measured and these values are correlated with the appropriate flame parameter.

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Copyright © 2005 by American Society of Mechanical Engineers
Topics: Flames , Methane
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References

Figures

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Figure 1

Laminar flame propagation in a stoichiometric methane-air (ϕ=1.0) premixture at an initial temperature of 300K and pressure of 0.1MPa. First image corresponds to the spark ignition and the time interval between the images are 0.76ms, and the size of the circular window is 150mm in diameter.

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Figure 2

Laminar flame propagation in a lean methane-air (ϕ=0.8) premixture at an initial temperature of 300K and pressure of 0.5MPa. First image corresponds to the spark ignition and the time intervals between the images are 0.9ms, and the size of the circular window is 150mm in diameter.

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Figure 3

Schlieren image of methane-air flames at 300K, where flame is (a) not cellular, (b) cellular (size of the circular window is 150mm in diameter)

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Figure 4

Measured flame speeds at different flame stretch rates

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Figure 5

Variations of Markstein number with equivalence ratio

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Figure 6

Variations of Pecl with Mab for onset of the flame instability. Symbols correspond to initial conditions presented at Table 1

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Figure 7

Variation of dimensionless time, τcl¯, with Mab for onset of flame instability. Symbols correspond to initial conditions presented at Table 1

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Figure 8

Methane-air atmospheric flame propagation. Present work and that of (17)

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