Acoustically Coupled Combustion Dynamics of Laminar Coaxial Methane-Air Jets

Acoustic excitation of coaxial methane-air laminar jet diffusion flames is explored as a means of studying fundamental non-linear coupling in combustion instabilities. Several alternative injector geometries and operating conditions are examined, with differing annular-to-jet area ratios, velocity ratios, wall thicknesses and excitation conditions. Flame dynamics are quantified using high speed visible imaging, with proper orthogonal decomposition (POD) to analyze various dynamical responses. With increasing excitation amplitudes, flames undergoing transition from sustained oscillatory combustion to periodic lift-off and reattachment to eventual blow-off may be correlated with POD mode coefficient plots having characteristic signatures, including strange attractor-like shapes. Such transitions are altered for different injector geometries and velocity ratios, suggesting that flame stabilization and dynamical response may be correlated with injector configuration in an acoustically resonant environment, and that phase portraits representing this response can aid in developing topology-based reduced order models.