This experimental study focused on the coupling of transverse acoustic flow perturbations with two different fundamental phenomena that take place in combustion chambers: reactive, condensed-phase droplet combustion, and non-reactive shear-coaxial injection flows. The study on fuel droplet combustion characteristics examined the response and behavior of various burning fuel droplets during exposure to external acoustical perturbations. These liquid fuels included ethanol, methanol, aviation fuel (JP-8), liquid synthetic fuel derived from natural gas, and a blend of JP-8 and synfuel. The study examined combustion during excitation conditions in a closed waveguide in which the droplet was situated at or near a pressure node, where the droplet experienced the greatest effects of velocity perturbations, and at or near a velocity node (pressure antinode), where the droplet was exposed to minimal velocity fluctuations but maximum pressure fluctuations. A two-speaker configuration provided the means to produce a fairly symmetric acoustic field in the waveguide. In the absence of acoustic excitation, values of the measured droplet burning rate constant K were generally consistent with available values for the different fuels explored. During acoustic excitation of droplets situated in the vicinity of a pressure node or antinode, flame orientation was consistent with the sign of an acoustic radiation force acting on the burning system, creating conditions where the flame deflection switched, depending on the relative location of the droplet. The acceleration associated with the acoustic radiation force was estimated by measuring the degree of deflection that the flame underwent relative to an unforced flame. Although overall there were no significant variations in the measured K values with changing acoustic excitation, in some cases, locally increased K values were observed to be associated with larger measured acoustic accelerations.
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