The Influence Of Flame Stretch On Cellular And Pulsating Instability

Soledad

The onset of unstable cellular and pulsating
modes of flame propagation predicted for the
one-dimensional planar flame is expected to be
modified in the presence of aerodynamic
stretch, which is usually present in all practical
flames, and is manifested through flow nonuniformity,
flame curvature, and flame unsteadiness.
Indeed, theories by Sivashinsky et al.
and Bechtold and Matalon show that positive
stretch, which is the one associated with, for
example, the counterflow flame and the outwardly-
propagating spherical flame, tends to
suppress cellular C, while negative
stretch promotes it. Regarding pulsating instability,
a numerical study  on outwardly propagating
spherical flames with one-step chemistry
indicates that oscillation is promoted at small
radii, hence strong positive stretch, and is
damped at large radii. Thus, in terms of positive/
negative nature of the stretch, the influence
of stretch on pulsating instability appears to be
completely opposite to that on cellular instability.