Experimental Study On Vertical Combustion Characteristics Of External Wall Insulation Materials Under Open-hole Condition

With the rapid development of social productivity,the processes of industrialization and urbanization in various countries are accelerating.The application of exterior wall insulation system,as the core component of building energy conservation,has been developed rapidly in the construction industry.However,the fire risk of insulation materials is very high,so it is of great significance to carry out experimental researches on exterior wall insulation materials fire.Which is helpful to predict the fire development process of external wall insulation materials,and will provide a theoretical foundation for the fire safety design of external wall insulation system.In this research,the combustion behaviors of XPS foam are studied experimentally.Through the pyrolysis and ignition experiments of XPS samples,it is found that the ignition temperature of XPS sample is 380? and the combustion heat is 37.357 MJ/kg under the experimental conditions.The pyrolysis process can be divided into four stages: dehydration stage,stabilization stage,rapid weightlessness stage and slow weightlessness stage.The change of sample mass is mainly occur in the rapid weightlessness stage,with the proportion of weightlessness 87.75%.Through the analysis of TG curve and DTG curve,it is concluded that there is a maximum weight loss rate in the pyrolysis process.And the corresponding temperature is about 385? which locates in the rapid weightlessness stage.By combining the analysis of the TG curve and DTA curve,we discover that there are two distinct endothermic peaks and exothermic peaks in the pyrolysis process.Generally speaking,the pyrolysis process of XPS materials is an exothermic process.The vertical flame spread experiments of insulation materials at different opening heights are carried out on the self-made experimental platform.It is found that the success rate of flame spread is 100% when the heights are less than 5 cm,indicating that the flame can spread from the lower part to the upper part successfully.When the heights are more than 8 cm,the flame can't spread successfully.When the height is 6 cm and 7 cm,the success rate of flame spread is 50% and 25% respectively.Based on the experimental results of vertical fire spread of insulation materials at different opening heights,the vertical fire spread experiments under open-hole conditions are carried out.It is found that the flame front,pyrolysis front and average flame height increase first and then decrease with the increase of porosity,and reaching the highest value when the porosity is 35%.This trend is caused by the competition between the promoting and inhibiting effects of hole.In this paper,the temperature field is recorded and analyzed by the thermocouple testing system.By comparing the sample(P=35%)surface temperature at different measuring positions,it is found that the maximum temperature between two holes is higher than that at the left side position.By studying the flame temperature field,we conclude that the flame maximum temperature varies with measuring positions,and the average values of the flame maximum temperature increase first and then decrease with the increase of the porosity.The heat transfer model of flame to sample is established,and the accuracy of this model is verified by experiments.It is found that both theoretical and experimental values increase first and then decrease with the increase of porosity.When the porosity is 35%,both theoretical and experimental values reach a critical maximum.