Stabilization mechanism of lifted flame edge in the near field of coflow jets for diluted methane

Stabilization mechanism of lifted flames in the near field of coflow was studied for methane fuel diluted with nitrogen. The lifted flames were observed only in the near field of coflow jets until blowout occurred in the normal gravity condition. To elucidate the stabilization mechanism for the stationary lifted flames of methane having the Schmidt number smaller than unity, the behavior of the flame in the buoyancy-free condition and unsteady propagation characteristics after ignition were examined numerically at various conditions of jet velocity. The buoyancy played an important role for the flame stabilization of lifted flame in the normal gravity, in such a way that the flame becomes nozzle attached in the microgravity. The stabilization mechanism was due to the variation of the propagation speed of lifted flame edge with axial distance from the nozzle in the near field of coflow as compared to the local flow velocity variation at the edge. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).