THE EFFECT OF ACOUSTICS ON AN ETHANOL SPRAY FLAME IN A PROPANE-FIRED PULSE COMBUSTOR

The influence of an acoustic field on the combustion characteristics o f a hydrogen-stabilized ethanol spray flame has been experimentally in vestigated using a phase-Doppler particle analyzer in a propane-fired, Rijke-tube, pulse combustor. The controlled sinusoidal acoustic field in the combustor had a sound pressure level of 155 dB and a frequency of 80 Hz. Experiments were performed to study the effect of oscillati ons on Sauter-mean and arithmetic-mean diameters, droplet velocity, an d droplet number density for the present operating conditions of the R ijke-tube combustor. Similar measurements were also performed on a wat er spray in the propane-fired reactor to study the effect of the acous tic field on the atomization process for the nozzle type used. Spectra l analysis of the droplet axial velocity component for the oscillating conditions revealed a dominant frequency equal to the frequency of th e sinusoidal acoustic wave in the combustor. The Sauter-mean diameter of the ethanol spray decreased by 15%, on average, in the presence of the acoustic field because of enhanced evaporation, while the droplet arrival rate at the probe volume increased due to changes in the flame structure. Analysis of the measured size distributions indicated that under an oscillating flow there was a larger population of droplets i n the diameter range of 3-20 mu m. Experiments conducted with the wate r spray indicated that the oscillations did affect droplet size distri butions in the ethanol spray due to enhanced evaporation caused by the relocation of the flame front inside and around the spray cone. (C) 1 997 by The Combustion Institute.