Acoustic kinetic energy and soot suppression efficiency of acetylene diffusion flame under acoustic excitation at varying resonant frequencies in Rijke tube

Abstract

The acoustic kinetic energy and soot suppression efficiency of acetylene diffusion flame under acoustic excitation at varying resonant frequencies in Rijke tube is investigated experimentally. The acoustic kinetic energy is introduced for the first time to explain the mechanism of soot suppression by acoustic oscillation. The soot suppression efficiency and acoustic kinetic energy is investigated by changing the acoustic parameters and the length of the Rijke tube. The results show that the efficiency of the soot suppression and the acoustic pressure increase significantly at the resonant fundamental frequency (167 Hz and 185 Hz) and resonant frequency (346 Hz and 373 Hz). The standing wave at the resonant fundamental frequency is a half wave, while the standing wave at the resonant frequency is a full wave. Soot suppression efficiency and acoustic kinetic energy reach the maximum at the wave nodes. When the efficiency of soot suppression is the same, the acoustic kinetic energy at the resonant frequency is twice that at the resonant fundamental frequency at the wave nodes. The flame brush, flame fluctuation velocity and the flame temperature are studied in detail by changing the acoustic parameters. The results show that the efficiency of soot suppression increase with the increase of flame fluctuation velocity and flame temperature. This is considered that the acoustic kinetic energy accelerates the flame fluctuation velocity which enhances the heat and mass transfer in the combustion field, resulting in an increase in the flame temperature, thereby soot is re-oxidized. This study can provide some reference for the practical application of acoustic oscillate combustion in soot suppression.