Solid fuel diffusion flame measurements of acoustics and visible dynamics

Though wildland fires are known to produce a myriad of sounds, current understanding of sound-generation mechanisms from solid fuel combustion, as found in wildland fires, is limited. Our goal is to better characterize the acoustic emissions from these transient events and the underlying dynamics responsible for sound generation. Our team performed simultaneous acoustical and optical measurements of laboratory-scale fires at the United States Forest Service Forest Products Laboratory. Corresponding heat release rates (HRR) were determined using oxygen consumption calorimetry. Excelsior was used as solid fuel, allowing careful control of fuel geometry, porosity, mass, and burn duration. The controlled environment allowed for repeatability of the burns with consistent fire dynamics and sound levels. The time evolution of the overall sound levels was highly correlated with the overall visible light intensity and HRR of the solid-fuel fires. The HRR and solid-fuel geometry provided good scaling of the measured sound levels, which peaked in the infrasound regime and continued to roll off through the audible frequency range.