Theory of Interactive Combustion of Counterflow Premixed Flames

The extinction characteristics of two interacting premixed flames in counterflow configuration is investigated within the framework of large activation energy asymptotics. The major modes of interactive combustion analyzed include (a) two lean premixed flames, (b) two rich premixed flames, and (c) a lean premixed flame and a rich premixed flame separated by a diffusion flame. It is found that regions corresponding to symbiotic combustion of two lean or two rich premixed flames exist, where either flame will extinguish in the absence of the other. Furthermore, conditions for the existence of superadiabatic flames within mixtures outside of the conventional flammability limit compositions are established. Comparison of the results with the experimental data on extinction of counterflow methane-air flames show good agreement for lean but not rich mixtures; the inadequacy is believed to be caused by the assumption of unity Lewis number and identical kinetic mechamism for lean and rich flames made in the theory. Practical implications of flame interaction on combustion in inhomogeneous mixtures and the modeling of turbulent flames are discussed.