This paper describes theoretical and experimental observations of combustion oscillations produced in a continuously mixed, jet-stirred combustion system. This work is distinct from other investigations of pulse combustion, because it is shown both theoretically and experimentally that combustion oscillations can be produced with a steady supply of fuel and air, requiring no mechanical or aerodynamic valves. The theory is a direct extension of thermal theories of combustion in back-mixed reactors, extended to include the unsteady behavior of the combustor and tailpipe. Because of the demonstrated effect of heat transfer on the oscillations, the name thermal pulse combustion is chosen to describe these oscillations. Effects of friction in the combustor tailpipe, heat loss from the combustion zone, and flow rate, are investigated theoretically. Depending on operating parameters, oscillating combustion, steady flames, or blow-out are all predicted. The effects of finite mixing rate are investigated by specifying a mixing time. Results of the simulation are then favorably compared to laboratory observations of a combustor operating with parameters similar to those used in the numeric model. Laboratory observations confirm that large amplitude oscillations can be produced in a jet-mixed combustor with a steady supply of fuel and air. Laboratory observations show qualitative agreement with predictions, and reasonable quantitative agreement at select conditions.
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