title: Role of buoyant flame dynamics in wildfire spread.
abstract: Large wildfires of increasing frequency and severity threaten local populations and natural resources and contribute carbon emissions into the earth-climate system. Although wildfires have been researched and modeled for decades, no verifiable physical theory of spread is available to form the basis for the precise predictions needed to manage fires more effectively and reduce their environmental, economic, ecological, and climate impacts. Here, we report new experiments conducted at multiple scales that appear to reveal how wildfire spread derives from the tight coupling between flame dynamics induced by buoyancy and fine-particle response to convection. Convective cooling of the fine-sized fuel particles in wildland vegetation is observed to efficiently offset heating by thermal radiation until convective heating by contact with flames and hot gasses occurs. The structure and intermittency of flames that ignite fuel particles were found to correlate with instabilities induced by the strong buoyancy of the flame zone itself. Discovery that ignition in wildfires is critically dependent on nonsteady flame convection governed by buoyant and inertial interaction advances both theory and the physical basis for practical modeling.
authors.affiliation: Missoula Fire Sciences Laboratory, US Forest Service, Missoula, MT 59808; mfinney@fs.fed.us.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Finney
authors.affiliation: Missoula Fire Sciences Laboratory, US Forest Service, Missoula, MT 59808;
authors.forename: Jack D
authors.initials: JD
authors.lastname: Cohen
authors.affiliation: Missoula Fire Sciences Laboratory, US Forest Service, Missoula, MT 59808;
authors.forename: Jason M
authors.initials: JM
authors.lastname: Forthofer
authors.affiliation: Missoula Fire Sciences Laboratory, US Forest Service, Missoula, MT 59808;
authors.forename: Sara S
authors.initials: SS
authors.lastname: McAllister
authors.affiliation: Department of Fire Protection Engineering, University of Maryland, College Park, MD 20742-3031;
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Gollner
authors.affiliation: Department of Fire Protection Engineering, University of Maryland, College Park, MD 20742-3031;
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Gorham
authors.affiliation: Department of Mechanical Engineering, University of Kentucky, Lexington, KY 40506-0503.
authors.forename: Kozo
authors.initials: K
authors.lastname: Saito
authors.affiliation: Department of Mechanical Engineering, University of Kentucky, Lexington, KY 40506-0503.
authors.forename: Nelson K
authors.initials: NK
authors.lastname: Akafuah
authors.affiliation: Department of Mechanical Engineering, University of Kentucky, Lexington, KY 40506-0503.
authors.forename: Brittany A
authors.initials: BA
authors.lastname: Adam
authors.affiliation: Department of Mechanical Engineering, University of Kentucky, Lexington, KY 40506-0503.
authors.forename: Justin D
authors.initials: JD
authors.lastname: English
mesh_terms: D018481:Convection; D005390:Fires; D006358:Hot Temperature; D021621:Imaging, Three-Dimensional; D055585:Physical Phenomena; D013696:Temperature; D013781:Texas; D013997:Time Factors; D014919:Wind
keywords: buoyant instability; convective heating; flame spread; wildfires