Flame-vortex interactions - Effects of buoyancy from microgravity imaging studies

The interaction between a single toroidal vortex and a laminar flame in a lean premixed propane-air mixture was visualized in order to understand how each vortex in a turbulent flow wrinkles, stretches, and possibly extinguishes the flame. Both microgravity and 1-g images were obtained to identify the role of buoyancy forces, which are significant in laboratory flames and in many industrial flames. Buoyancy forces affect the degree of flame wrinkling, the vorticity produced by the flame due to baroclinic torques, the flame stability, and the flame velocity. In the present experiment, all components of flame stretch, strain, and vorticity can be measured from a single PIV image because the interaction is axisymetric. Results indicate that microgravity conditions greatly augment the flame wrinkling process and therefore turbulent flames in microgravity could propagate significantly faster than those in 1-g, which is a potential safety hazard. A new mechanism is identified by which buoyancy retards flame wrinkling; buoyancy produces new vorticity (due to baroclinic torques) that oppose the wrinkling and stretch imposed by the original vortex. (Author)