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The effect of thermal expansion on diffusion flame instabilities†

Published online by Cambridge University Press:  18 March 2010

M. MATALON*
Affiliation:
Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
P. METZENER
Affiliation:
Faculté des Sciences de Base, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
*
‡Email address for correspondence: matalon@illinois.edu
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Abstract

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In this paper we examine the effect of thermal expansion on the stability of a planar unstrained diffusion flame and provide a comprehensive characterization of diffusive-thermal instabilities while realistically accounting for density variations. The possible patterns that are likely to be observed as a result of differential and preferential diffusion are identified for a whole range of parameters including the distinct Lewis numbers associated with the fuel and oxidizer, the initial mixture strength and the flow conditions. Although we find that thermal expansion has a marked influence on flame instability, it does not play a crucial role as it does in premixed combustion. It primarily affects the parameter regime associated with the onset of the instabilities and the growth rate of the unstable modes. Perhaps the most surprising result is that its has a different influence on the various modes of instability – a destabilizing influence on the formation of cellular structures and a stabilizing influence on the onset of oscillations.

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Papers
Copyright
Copyright © Cambridge University Press 2010