Flame propagation and extinction in large-scale vortical flows

It is shown that the propagation speed of the premixed gas flame spreading through a time-independent, space-periodic array of large-scale vorticities is a nonmonotonic function of their intensity. For moderately strong vorticities their intensification results in the flame speed enhancement accompanied by shedding of islands of unburned gas. Yet there is a certain level of stirring at which the flame speed reaches its maximum. Any further increase in the stirring intensity leads to a drop in the flame speed, followed, for mildly nonadiabatic systems, by flame extinction. The relation of these findings to the classical theory of planar counterflow flames is discussed. The study is motivated by the experimentally known phenomenon of flame extinction by turbulence. (C) 1999 by The Combustion Institute