Condensed Phase Combustion in the Presence of Altered Acoustic Disturbances

This experimental study focuses on fuel combustion characteristics of liquid droplets and solid spheres during exposure to external acoustic disturbances generated within a closed acoustic waveguide. The study examines combustion during excitation conditions in which the droplet or sphere is situated at or in the vicinity of a pressure node (PN) or a pressure antinode (PAN). During such acoustic excitation, flame orientation is observed to be consistent with the sign of a theoretical acoustic acceleration, analogous to a gravitational acceleration, acting on the burning system. Yet experimentally estimated acoustic accelerations differ quantitatively from that predicted by one theory of the acoustic radiation forces\footnote{Tanabe, et al., {\bf PCI}, 2000}. Altered orientations of the waveguide are used to examine the nature of acoustically generated forces. The present experimental configuration provides a useful test bed for the evaluation of the response of different burning fuels to an acoustically resonant environment, including conditions leading to flame extinction, and can be used to explore a range of condensed phase combustion processes during such acoustic coupling.