The Unstable Behavior Of Cellular Premixed flames Induced By Intri

Soledad

In premixed flames propagating at subsonic
speed, intrinsic instability always appears. The basic
types of phenomena to account for the intrinsic
instability of premixed flames are hydrodynamic
and diffusive-thermal effects.The hydrodynamic
effect is caused by the thermal expansion
through the flame front and is the most essential
factor in the flame instability, since the combustion
reaction is exothermic and all premixed
flames are accompanied by thermal expansion.
Thus, we cannot study the instability of premixed
flames without taking account of the hydrodynamic
effect. The diffusive-thermal effect, together
with the hydrodynamic effect, is significant for
intrinsic instability. This effect is caused by the
preferential diffusion of mass versus heat and
has a destabilizing influence on Lewis numbers
of the deficient reactant lower than unity, where
the Lewis number is defined as the thermal diffusivity
divided by the diffusion coefficient. Thus,
hydrogen–air lean premixed flames are strongly
affected by the diffusive-thermal effect. Hydrodynamic
and diffusive-thermal effects have a great
influence on the formation of cellular-flame fronts
and on the combination and division of cells, so
that we have to clarify the instability induced by
these effects to control the unstable behavior of
cellular flames.