Hydrodynamic Instabilities in Flames

Abstract

The strong coupling of a flame to the flow through which it propagates is caused primarily by the thermal expansion of the gas undergoing chemical reaction. This coupling has a prominent effect on the response of a flame to hydrodynamic disturbances. In the first stability analysis carried out independently by Darrieus (1938) and Landau (1945), the linear stability of a plane unbounded flame was studied. Their results reveal that the effect of thermal expansion is always to destabilize the flame. This instability is commonly referred as to the hydrodynamic instability; see the discussion on Flame Stability by J. Buckmaster in these proceedings. Since all combustion processes are accompanied by thermal expansion, the hydrodynamic instability is always present.However, other effects such as curvature, flame stretch, gravity and diffusion, may have stabilizing influences.These effects are briefly examined in the following. Hydrodynamic effectsA steadily propagating plane adiabatic flame is characterized by two parameters: the temperature rise across the flame or the flame temperature and the propagation speed; both are properties of the o combustible mixture. Whereas the flame temperature T f is calculated from an overall energy balance across the combustion field the internal structure of the