An Investigation on Laminar Premixed M-shaped Flame Response to Velocity Oscillations

The response of an M-shaped premixed flame anchoredsimultaneously on the nozzle rim and on the central rodof an annular burner to upstream velocity perturbationshas been characterized as a function of excitationfrequency, and flame angle. Self-excited oscillations inlow emission, premixed combustion systems are oftencaused by feedback between unsteady heat release ratesand velocity perturbations. Using an analytical modelbased on linearization of the G-equation for inclinedflames, the combustion response functions of a simple M-flame can be derived by separately integrating therate of heat release over the two branches of the flamezone. It is shown that the long M-shaped flame response to convected velocity perturbations exhibit lessoscillatory pattern with a higher overshoot inthe magnitude of its transfer function with respect to a shortM-flame.