157. AERODYNAMIC EFFECTS ON FLAME SPREAD AND EXTINCTION
Name: Luca Carmignani
Grad Year: 2020
Flame-spread over solid fuels in presence of an opposed flow field has received increasing attention over the last forty years, due to its implications in fire safety and combustion of solid propellants. The opposing flow can be due to a buoyancy-induced flow, forced flow, or a combination of them. A vertical wind tunnel was used to generate flow velocities in the range of 0-100 cm/s, against which a laminar flame spread along the fuel sample. In this work the influence of the boundary layer over the sample on the flame-spread rate has been experimentally investigated using cellulosic fuel (filter paper) and PMMA; results show that the actual velocity seen by the flame embedded in the boundary layer (called equivalent velocity) leads to a decreasing spread rate while the flame is going downward, even for constant free stream velocities. This behavior can be justified relating the residence time, and therefore the Damköhler number, to the equivalent velocity; thus the flame enters in the kinetic regime before expected, eventually causing local blow-offs and the complete extinction of the flame. The distance from the sample edge to the point where extinction occurred increased with higher flow velocities, suggesting that extinction could be determined by a critical equivalent velocity; an easy-to-use formula has been proposed accordingly with results for the cellulosic fuel, in order to predict the length over the sample at which extinction occurs knowing the free stream velocity.
Industry Application Area(s)
Aerospace, Defense, Security | Fire Safety