Study On The Behavior Of Vertical Downward Flame Spread In Typical Thermal-thin Materials

With the development of the times,more and more large volume and multifunctional public buildings were built.The number and variety of flammable and combustible materials used in the building are rapidly increasing,and the materials used as interior decoration are thin materials with flammable and combustible,such as plexiglass,decorative cords,advertising cloth and wallpaper,ect.This thin materials can be classified into two categories: non-charring and charring materials.These flammable thin materials will quickly burnout once they were exposed to fire or hot objects,and ignite adjacent combustible substances,then cause fire of large area.At home and abroad,the research on thin material is based on vertical upward flame spread of some size material.As well as the study of flame spread with wall or two-face exposed to air.The theoretical and experiment research on vertical downward flame spread under different limited distances and width coupling is lacking.In this paper,the experiment of vertical downward flame spread about PMMA and cotton are designed.The experiment was set up to 4 limited distances,7 mm,13 mm,19 mm and 25 mm respectively.At the same time set the width of 3,50 mm,100 mm and 150 mm.The group of 24 and times of 72 were carried on experiments about vertical downward flame spread,explored the the vertical downward flame spread characteristics about PMMA and cotton under the condition of different limited distances and width.The main research is about flame spread characteristic parameters including flame front,flame height Hf,pyrolysis striker xp,flame spread rate vp,burnout striker xb and pyrolysis height Lp.The experimental results show that the flame shape of PMMA is serrated,and the maximum varies amplitude of flame front angle is when the limited distance is 13 mm,while the width of it is 150 mm.The flame shape of cotton is rectangular.When the width is 50 mm,the flame front angle is closely equal to 100 mm;the lowest amplitude of the front angle is 13 mm and the maximum variation is 7 mm.For PMMA,when the width is same,the threshold of the limited distance is 13 mm,and the critical value of the characteristic parameters is at the distance,and the minimum is at the distance of 7 mm.The overall performance is that the characteristic parameters first increase and then decrease with the increase of limited distances.When the limited distance is same,the pyrolysis striker,the burnout striker and the flame spread rate increase with the width increasing,and both the growth mode of them are approximate power function,and its general formulas arex_i=a_i+b_i·t~c_i，v_j=a_i·t~b_i.The flame height and pyrolysis height of the width of 150 mm is the largest,and the width of 100 mm is the smallest.The largest dimensionless flame height is width of 50 mm,and the smallest is 100 mm.For cotton,when the width is same,the threshold of the limited distance is 13 mm,and the smallest value of the characteristic parameters is at the distance,and the maximum is at the distance of 7 mm.The overall performance is that the characteristic parameters first decrease and then increase with the increase of limited distances.When the limited distance is same,the pyrolysis striker,the burnout striker and the flame spread rate increase with the width increasing,and the growth pattern of them are the approximate one function respectively,and its general formulas are x_j=a_j+b_j·t，v_j=a_j+b_j·t.The flame height and pyrolysis height decreased with the increase of width.