Acoustic flame extinction by the sound wave or speaker-induced wind?

Many literature studies explored acoustic-driven flame extinction via different experimental techniques, but the interpretation of results and the underlying mechanism are still unclear. In this work, a candle flame (20 W) is tested in two kinds of sound fields, one developing freely and the other guided by a cylindrical tube. Results show that the flame exhibits completely different fluctuations at the same sound pressure, indicating the observed flame extinction is irrelevant to sound waves (particle velocity ∼10−2 m/s at 100 dB). The oscillating airflow (∼0.5 m/s at 100 dB) generated by the vibration of the speaker diaphragm is the real cause of flame fluctuation and extinction. Moreover, using a cylindrical tube can enhance the diaphragm-induced airflow and promote flame extinction.