Margolis (1980) used realistic kinetics to model a hydrogen-oxygen flame in the presence of a burner. His numerical results of an oscillating flame front suggested that pulsating flames were indeed accessible in laboratory experiments. Our previous experiments on methane-air flames showed that pulsating flames occur throughout parameter space and that a variety of spatial and temporal characteristics are possible.
Buckmaster (1982) included the effect of heat loss to the burner and computed the changes to the stability boundaries of both pulsating and cellular flames. He showed that the stability boundaries are pushed toward each other and, for sufficiently strong heat loss, can be made to overlap, indicating an interaction between the two types of modes. The water-cooled porous plug Pagni burner provides a sufficiently large heat loss to move the stability boundaries for pulsating flames to accessible values of parameters, including an overlap with those of cellular flames. Another consequence of this overlap is that a steady flame front is not observed as the flow rate is varied. McIntosh (1985) made similar findings using the hydrodynamic model as the source of the instability. He incorporated a realistic model of the flow created by the porous plug.
Pulsating-cellular states are found in a parameter range near the onset of cellular flames, for both isobutane and propane flames. The radial mode, which occurs for lean methane-air flames, is found near the extinction boundary in rich propane-air and isobutane-air flames, in agreement with the thermodiffusive model. The interaction between the radial mode and the ordered cellular state can be adjusted by varying either the flow rate or the equivalence ratio. The spatial character of the pulsating-cellular state changes with the strength of the interaction.