Experimental Study On The Canyon Fire Spread By Line Ignition

Surface fire spread is the most important form of wildfire,in which terrain condition is an important factor affecting fire spread.Most of the previous work is limited to fire spread on flat or upslope conditions,while the understanding of fire spread in the special terrain of canyons is not yet in-depth.In this work,the canyon fire spread experiment table is used,and pine needles are used as fuel.Different slope conditions(the central slope:0°,10°,20°,30°,the lateral slope:10°,20°,30°),fuel bed were(1.5,3.0,4.0,8.0 m)and fuel laying method(single-side and double-side fuel bed)are employed in canyon fire experiments.The fireline contour,the fire spread rate,the combustion characteristics of the fuel and the flow velocity were investigated,and the fuel preheating mechanism was analyzed.In the double-sided fuel bed fire spread experiment,when the central slope angle is higher than 10°,as the lateral slope angle increases,the fire head moves to both sides of the fuel bed,the fire line presents a significant concave shape,and the interaction between flames on both sides make the fire head deviate from the maximum slope line.In the one-sided fuel bed spread experiment,the fire track spread along the direction of the maximum slope line of the canyon.The rate of fire spread increases with increasing central slope angle and lateral slope angle.When the central slope angle is higher than 20° and the lateral slope angle is higher than 10°,the canyon fire ignited by the line fire spreads and produces an eruptive fire.The unsteady canyon fire spread can be divided into a developing stage and a fast spreading stage,and the fire spreading rate in the fast spreading stage is about 10 times higher than that in the developing stage.With the increase of the lateral slope angle,the lateral air entrainment is limited,and the process of fire spread is accompanied by the phenomenon of flame attachment.The gas velocity in front of the flame along the centerline of the fuel bed increases with the increase of the central slope angle and decreases with the increase of the lateral slope angle.When the fuel bed width increases from 3.0 m to 8.0 m,the fire spread rate and the peak value of the forward gas flow rate all increase.When the central slope is 30°,the lateral air entrainment is weakened,so that the fireline contour changes from an inverted V shape to a positive V shape.With the increase of the central slope angle and the lateral slope angle,the convective heating effect is enhanced,and strong convective heating is generated in the fire head area,which is the physical mechanism for inducing eruptive fire.Convective heating works over long distances.