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Wildfire Seminar Series: Matthias Ihme -- X-ray measurements to understand the science of fire spread by ember transport

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Abstract: The severity and frequency of large wildfires have increased significantly in the past two decades, which is largely attributed to poor forest management and climate change but also to growing population and human activities in the wildland-urban interface. The main mechanisms for the spread of wildfires are direct flame impingement, radiation, and firebrand showers. Firebrands are hot airborne particles that are generated from burning vegetation and flammable materials. Firebrands have been identified as a main source of wildfire-spread disasters and were found to be responsible for the loss of more than half of the buildings in fires. Therefore, understanding the fundamental physical processes underlying the ember combustion is therefore increasingly relevant. In particular, accurate experimental measurements are critical to guide our understanding of fuel consumption. However, because of the multiphase nature of biomass combustion, the release of smoke, and the requirement for optical access in traditional diagnostic techniques, acquiring detailed experimental measurements remains challenging.

This presentation provides an overview of recent development of 3D X-ray computed tomography (CT) to experimentally investigate smoldering and combustion of solid fuel particles. By temporally resolving the surface recession of solid fuel material, the local consumption rates are extracted at the micro-meter spatial resolution. By diluting the ambient flow with Krypton, the X-ray measurements enable simultaneous estimations of the 3D gas-phase temperature field. Using these high-resolution measurements, we discuss effects of air dilution, heating rate, and biomass properties on smoldering and combustion processes. These measurements provide unique insights on the pore-scale structural changes occurring during the primary pyrolysis and subsequent char devolatilization, allowing for further investigations of state-of-the-art models of smoldering.

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