Fluctuation and extinction of laminar diffusion flame induced by external acoustic wave and source

Caiyi Xiong,Xinyan Huang,Haoran Fan,Yuji Nakamura,Yanhui Liu

doi:10.1038/s41598-021-93648-0

Caiyi Xiong, Xinyan Huang + Show 3 more

Open Access

https://doi.org/10.1038/s41598-021-93648-0

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Abstract

Acoustic wave can destabilize the flame and has a potential in firefighting, but the influences of the sound source and its frequency are still poorly understood. This work applies a loudspeaker to extinguish a laminar diffusion propane flame of 5–25 mm high, where the local sound frequency is 50–70 Hz and sound pressure is 0.8–3.2 Pa (92.0–104.1 dB). Results reveal a constant flame pulsating displacement at the extinction limit, independent of the sound environment used. Such a flame pulsating displacement is found to be caused by the motion of the speaker membrane (or diaphragm) and its induced wind, which could be two orders of magnitude larger than the displacement of the air that transmits acoustic wave. Thus, under the influence of sound source, a critical flame strain rate, stretched by the pulsating airflow, can be formulated to characterize the blow-off limit better than the local sound pressure. The sound source with a lower frequency can produce larger pulsating displacements of both membrane and flame, and thus promoting extinction. This work improves the understanding of flame dynamics under the external sound field and source, and it helps establish a scientific framework for acoustic-based fire suppression technologies.

Highlights

Acoustic wave can destabilize the flame and has a potential in firefighting, but the influences of the sound source and its frequency are still poorly understood
When increasing the sound pressure to 1.8 Pa, a successful extinction of a 15-mm flame can be seen in Fig. 3b, where the flame fluctuation still existed, but the flame was deflected far away from the nozzle and could no longer be anchored, and eventually, acoustic extinction occurred
This work experimentally explored the impacts of the sound source on the extinction of laminar diffusion flames

Summary

Introduction

Acoustic wave can destabilize the flame and has a potential in firefighting, but the influences of the sound source and its frequency are still poorly understood. Results reveal a constant flame pulsating displacement at the extinction limit, independent of the sound environment used. The sound source with a lower frequency can produce larger pulsating displacements of both membrane and flame, and promoting extinction. McKinney and Dunn-Rankin[9] first used the low-frequency acoustic waves (75–135 Hz) to extinguish a methanol droplet flame They found that a higher sound pressure was required to extinguish the flame at a higher frequency and concluded that the extinction was caused by the acoustic-induced flame displacement from the fuel droplet. Two questions remain, (1) why a lower-frequency sound shows a better flame-extinction performance? and (2) what is the influence of sound source on acousticdriven flame extinction?

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