On the mechanism of bluff body flame stabilization at low velocities

Abstract

Previous workers on bluff body laminar flame stabilization have observed, under a wide variety of circumstances, flame sheets that were wrinkled into ‘nodal’ waves with well-defined wavelengths and velocities of propagation. In this paper, experiments are described that explain the observed wave forms. It is believed that they are forced, unstable, propagating, interfacial waves—forcing being caused by the oscillation of the point of attachment of the flame in the boundary layer and wake surrounding the flameholder. Spark shadowgraphs are presented to support this conclusion. Data are presented to show the dependence of the frequency of oscillation of flow velocity, air/fuel ratio, and sphere diameter. Flameholding phenomena and the formation of ‘envelope’ flames are also discussed.