Dr. Luca Carmignani

Assistant Fire Advisor

Wildland-Urban Interface

University of California

Agriculture and Natural Resources

Abstract

Over the past decade, California and other Western states have experienced an increase in tree mortality, resulting in a build-up of downed fuels on forest floors. Unlike fine grasses and shrubs that are often consumed by the flaming front of a wildfire, downed fuels can burn for extended periods in the smoldering regime. Smoldering occurs in the solid phase of the fuel and is characterized by lower temperatures, heat release, and spread rates than flaming combustion. However, it produces larger quantities of carbon monoxide and particulate matter, deteriorating air quality and compromising human health. External winds can influence the intensity of the smoldering process by bringing fresh oxidizer near the burning surface, potentially leading to a transition back to flaming. The enhanced convective cooling due to the wind, however, can slow down or even stop the smoldering process. The balance between enhanced oxidation and convective cooling depends on the geometry and size of the fuel, which determine the flow interaction with the external wind. A series of experiments was conducted using woody samples to investigate the influence of wind speed and fuel geometry on the smoldering process. Single sticks with variable thicknesses and lengths were placed in a wind tunnel at different distances from each other to simulate the presence of a crevice in large woody fuels, and to study the conditions under which the smoldering process is self-sustained. The larger mass loss rates and post-combustion product concentrations at higher wind speeds indicate that the smoldering process becomes more intense. Nevertheless, the results are highly dependent on the spacing between the sticks, suggesting that a gap significantly impacts the balance between heat released and heat lost. These findings may contribute to a better understanding of sustained smoldering for woody fuels, as well as the conditions that can lead to flaming transition.

Biography

Luca has recently joined the University of California Cooperative Extension at the South Coast Research and Extension Center as an Assistant Fire Advisor to promote fire resilience for the Wildland-Urban Interface in Southern California. Previously, he was a postdoctoral researcher in the Berkeley Fire Research lab at the University of California, Berkeley. Luca's research is focused on fire and combustion applications, from wildland fires to material flammability. He graduated from the Joint Doctoral Program between the University of California, San Diego, and San Diego State University in Engineering Sciences, after obtaining his bachelor’s and master’s degrees in Aerospace Engineering from the University of Pisa (Italy). Luca’s research interests include image analysis, computer programming, and scientific outreach.