Gravitational Effects on Partially Premixed Flames

Partially premixed flames are hybrid flames containing multiple reaction zones. These flames are of fundamental importance to the phenomena of nonpremixed flame stabilization and liftoff, spray combustion, and localized extinction and reignition in turbulent flames. The structure of partially premixed flames is determined by the interactions that arise among these zones due to the synergy between the thermochemistry and the heat and mass transport. The interactions between the various reaction zones occur due to the advection and diffusion of both heat and mass. These effects are strongly influenced by flow dilation and gravity, as well as flame curvature and differential diffusion. In this research, we are investigating the structures of partially-premixed flames under normal gravity and microgravity conditions.

A combined experimental-numerical study is being carried out to examine gravitational effects on the structure and stability of hydrogen- (i.e., very diffusive) methane-, and propane-air (i.e., least diffusive) flames that are established on a slot burner. Experimental measurements involve those of velocity, species, temperature, radiative emission, and chemiluminescence. Numerical simulations are based on the solution of multi-dimensional, transient, governing equations with detailed chemistry. A representative result showing differences between the topologies of 0- and 1-g partially premixed flames is presented in the figure. For more detailed results, the reader is referred to our publications given in the list of publications. A careful investigation of the interactions between transport, buoyancy, and thermal radiation will increase our understanding of these flames, resulting in better combustor design and fire safety solutions.