New instability modes of a diffusion flame near extinction

The linear temporal stability of a diffusion flame, modeled with a simplifi ed one-dimensional approach, in a two-dimensional mixing layer is investiga ted. In addition to the well-known "shear" or Kelvin-Helmholtz mode, which is also present in nonreacting flows, the current analysis reveals new "hea t release" or combustion modes for flames near the extinction limit, i.e., when the Damkohler number is low. For conditions near extinction, the shear mode is found to be damped and only the combustion modes are unstable. The fundamental destabilizing mechanism of these combustion modes is elucidate d. (C) 1999 American Institute of Physics. [S1070-6631(99)01910-8].