Study On Effects Of Widths And Restricted Distances On Linen Fabric Vertical Fire Spread And Self-blowing Extinguishing Behavior

With the development of the economy and the construction industry,the use of decorative materials is increasing,but at the same time,it also causes a large fire hazard,causing many fires,causing huge economic losses and casualties.The decorative materials include thin materials such as curtains,tablecloths,carpets,and wallpapers,and most of these materials are flammable.Once ignited,they are easily to spread rapidly and form large-scale three-dimensional fire.Therefore,it is necessary to study thin materials and understand their combustion mechanism,so as to provide a certain basis for building fire protection.Previous studies have focused on the vertical fire spread of solids under a single variable,but few on the vertical fire spread and self-blowing extinguishing behavior under multiple variables.In this paper,linen fabric was used as experimental material to study effects of width and restricted distance on vertical fire spread and self-blowing extinguishing behavior.Using the linen fabric experimental system to carry out experiments,and the experimental platform can realize flexible adjustment of width and restricted distance.The vertical fire propagation experiment of linen fabrics with different widths and different restricted distances was carried out.The experimental phenomena and the characteristic parameters of flame front,flame bottom,pyrolysis front,flame length and flame spread speed in the process of vertical flame spread were analyzed and compared.The causes of self-blowing extinguishing behavior were explained qualitatively using turbulent effect and Damkler numbers.It is found that the downstream flame spreading process of linen fabrics can be divided into three stages:the growth stage of double-sided flame spreading,the one-sided self-blowing stage and the one-sided flame spreading stage.At a restricted distance of 1 cm and 1.5 cm,self-blowing extinguishing occurred on the unconstrained side;at 2.5 cm,3 cm and 3.5 cm restricted distance,self-blowing extinguishing occurred on the restricted side.The entire self-blowing extinguishing process lasts for a short period of time between 2 and 5 s.In the growth stage of double-sided fire spread,the general formula for fitting pyrolysis front isX_p(28)a(10)bt~c.In the one-sided flame spreading stage,the general formula for fitting pyrolysis front is X_p(28)a(10)bt.The study on the spread of downstream flow and self-blowing extinguishing behavior under different restricted distance shows that when the self-blowing extinguishing occurs on the unrestricted side,the maximum flame length,maximum flame spread speed of the growth stage of double-sided flame spreading stage and the stable flame length and the steady flame spread speed of the one-sided flame spreading stage increase with the increase of the restricted distance.When the self-blowing extinguishing occurs on the unrestricted side,the maximum flame length of the growth stage of double-sided flame spreading stage increases with the increase of the restricted distance,but the pyrolysis front,stable flame length and the steady flame spread speed of the one-sided flame spreading stage decrease with the increase of the restricted distance.The study on the spread of downstream flow and self-blowing extinguishing under different widths shows that the height of pyrolysis front,the length of stable flame and the spread speed of stable flame decrease with the increase of width at the acceleration stage of double-sided flame spread and one-sided flame spread at a restricted distance of 1.5 cm.The height of pyrolysis front,the length of stable side flame and the spread speed of stable flame increase with the increase of width in the late growth stage of double side fire and one-sided flame spread at a restricted distance of 3 cm.The reason of self-blowing extinguishing is that the flame turbulence lengthens the flame length on the extinguishing side,which leads to the increase of buoyancy-induced velocity at the bottom of the flame,and then decreases the number of Damkeler,which makes the flame unstable.When the number of Damkeler decreases to a certain value,the flame will extinguish.