Self-excitation in laminar lifted free-jet propane flames diluted with nitrogen

Laminar lifted propane free-jet flames diluted with nitrogen were experimentally investigated to determine distinctive self-excitation regimes in the flame stability map and to elucidate the individual flame characteristics. Extremely low-frequency (<0.1 Hz) self-excitation was caused by conductive heat loss from the premixed wings to the trailing diffusion flame and could be explained by a proposed mechanism for edge flame extinction during triple-flame propagation as well as flame-front propagation. A newly observed heat-loss-induced flame blow-out mechanism was related to conductive heat loss from the premixed wings to the trailing diffusion flame. Additional self-excitation prior to flame blow-out was caused by buoyancy and also significantly affected by the conductive heat loss from the premixed wings to the trailing diffusion flame. This was explained in terms of triple-flame propagation and flame-front propagation. Self-excitation obtained in laminar lifted propane free-jet flames diluted with nitrogen was characterized by functional dependencies of the Strouhal number with related parameters.