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Lulu Sun
Experimental and Theoretical Investigation of Fire Behavior in Live Fuels Abstract The effects of varying physical characteristics of fuels and fuel beds on live fuel burning and whether live fuels differ fundamentally from dead woody fuels in their burning characteristics is not well understood. Towards this end, four common chaparral fuels prevalent in southern California, chamise, manzanita, ceanothus, and scrub oak were investigated by burning them in a cylindrical container. Mass loss rate, flame height, temperature, and velocity structures above the burning fuel bed were measured and analyzed. A linear regression fit was used to explain the observed time difference between when maximum flame height and maximum mass loss rate occurs, as a function of fuel moisture content. Two different methods were used to extract power laws for flame height of live and dead fuels. It was observed that the parameters defined in the well-known two-fifths power law for flame height as a function of heat release rate was inadequate for live fuels. As the moisture content increases, the heat release rate in the power law needs to be calculated at the time when the maximum flame height is achieved, as apposed to the maximum mass loss rate.
A PIV (Particle Image Velocimetry) system was used to obtain 2D instantaneous velocity fields in the vicinity of fire plumes. This enables analysis of periodic formation of vortical structures in planar buoyant plumes of chaparral fuels. The results obtained from PIV were then used to assess a thermal particle image velocimetry (TPIV) algorithm. This is a relatively inexpensive method that is used to estimate velocity fields using temporally varying temperature fields, captured by an infrared (IR) thermal camera. Time series vertical velocity profiles and time-averaged velocity vector fields are compared. The comparison demonstrates the applicability and performance of the TPIV algorithm in wildfire research.
A 3D computational model FIRETEC, developed originally by researchers at LANL was adapted to investigate fire spread through live chaparral. Specifically, the effect of varying environmental variables and physical characteristics of fuels on fire spread was examined. Results enable quantification of the effects of wind speed in enhancing heat transfer from the fire to unignited fuel ahead of the fire front. Increased fuel loading and packing ratio resulted in decreased rate of spread; while increased fuel moisture reduced the predicted rate of spread, consistent with laboratory scale experiments.
Wednesday, December 7, 2005
Engineering II Room 205
Start: 10:00 a.m. to 12:00 p.m.
(Refreshments will be served at 9:45 a.m.)
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