The Study Of Underside Flame Spread Process Over Walnut Wood Panels

With the social development and people's aesthetic enhancement,different types of building decoration tends to be more diversified.As the wood products' style are simple and fresh,people often fix wooden panels on the walls,roofs and floors.However,the wood products are flammable,once the fire happened,the flame will spread quickly to other place,thus more places will be ignited,causing a greater fire risk.At present,the researches about wood panels are more on the vertical flame spread or suspend flame spread phenomena.And experiment about the underside flame spread over wooden panels,also named ceiling flame spread,was still limited.Therefore,it is necessary to study the characteristics of underside flame spread.First,samples of 3.0-mm-thick wooden board were used in this research,and the underside flame spread characteristics of wood—a typical combustible solid—fixed at different angles without sidewalls were studied using digital images and infrared thermal imaging.This study demonstrated that the underside flame spread went through extinguished,stable combustion,and accelerated combustion stages for samples fixed at different angles,and a laminar flow was found to cause flame turbulence.The turbulence increased as the angle was increased from 300°up to 80°.The underside flame appeared turbulent and intermittent,and the flame length and pyrolysis region length were discovered to be positively correlated with the sample angle.As a novel finding,when the thermally thin wood fixed at the wall,it should be considered as thermally thick materials.The analysis of the underside flame spread behavior on the wood specimens demonstrated that the critical angle of the process is 30° and the critical velocity is 0.25 cm/s.Second,by comparing the upper surface and suspend flame spread,it is found that underside flame spread was more stable.Moreover,in the suspend flame spread process,the dominate flame will transform from undersurface to upper surface with the increase of the angle,and the critical angle is about 70 °.When the inclination angle is greater than 30 °,the flame length of the lower surface is smaller than the upper surface.When the inclination angle is less than 30 °,the flame of the lower surface will suddenly increase.In addition,in order to know the role of the pilot flame in the flame spread beginning stage,numerical simulation is used to study the flame influence on the wooden panels at different angles.It is found that the two kinds of flame have different ignition modes on the wood preheating zone.