Influences of Upstream Versus Downstream Heat Loss/Gain on Stability of Premixed Flames

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Abstract
Influences of upstream versus downstream volumetric heat loss/gain on the linear stability of laminar premixed flames are investigated. A single-step irreversible reaction governed by Arrhenius-type rate law is considered within the framework of a diffusional-thermal stability model. The resulting dispersion relations show that while both upstream and downstream losses enhance the tendency towards instability, downstream loss is more effective in promoting instability. The characteristics of cellular as well as the travelling-wave type instabilities in the presence of heat loss/gain from either the downstream or upstream side of the flame have been determined. Also, the impact of these various modes of heat loss/gain on the rate of growth of the characteristic cell size of cellular flames is assessed. The dispersion relation describing the stability of non-adiabatic flames with a two-reactant chemical model is determined as being similar to that corresponding to the single-reactant model. The practical implications of the results on the stability of flamelets occurring in turbulent combustion fields are discussed.

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