Research On Upward Combustion Characteristics Of Thermal Thin Material

With the development of the society, people’s aesthetic requirements have been improved, and much more thin finishing material has been widely used in the construction industry, such as thin plank, synthetic plastic sheet, organic glass, decorative fabric and so on. Because of its unique performance, organic glass has been favored by many manufacturers. Most of these materials are flammable. After ignited, they may spread quickly and lit up more fuel, for which they have great fire risk. However, at present, domestic and overseas research results are based on experiment about wall fires or fires burning without limits, lacking analysis and research between the two experimental conditions(considering the gap between fuel and wall). Nevertheless, a large amount of thin finishing material were arranged in this way, leaving some gaps between the walls, such as large plastic billboard installed on the mall exterior wall. Fires spread in this condition is much more complex and dangerous. Therefore, it is necessary to do more research about upward flame spread in different limited conditions of thin material.This paper studied characteristics of the typical thin material about combustion and upward flame spreading in different situations by combining small scale combustion characteristic experiment, exploratory fire spread test and numerical simulation. From experiment, the initial pyrolysis temperature of polymethyl methacrylate sheet is 340 ℃, temperature at maximum mass loss rate is about 375 ℃, and EHC is 24.4 MJ/kg. In this paper, 12 groups of combustion experiments have been carried out to explore the fire spread characteristics of PMMA when burning without limits and burning with limited distance of 0 mm, 2 mm, 4 mm, 5 mm, 7 mm, 10 mm, 13 mm, 16 mm, 19 mm, 22 mm, 25 mm respectively. It was found that flame height and flame spread rate increased with the limited distance at first, and then decreased with the limited range after reaching the critical value. Along with the rising of the limited distance, back flame height quickly jumped and became higher than front flame height, then after reaching the critical value, back flame height decreased with the limited distance, and kept the same height as front flame finally. From the experimental data, the time function of burnout height(xb), pyrolysis height(xp) and flame height(xff) met the laws of ic i i ix =a +b ×t, fire spread rate conformed to the laws of ci1i i iv b c t-= × ×, R2>0.9. Analysis showed that the length of flame(xff-xb) and pyrolysis area(xp-xb) increased with the limited distance, the ratios between them waved within 2 ~ 4 with the variational limited distance, and stabilized finally.Based on thin fuel combustion characteristic experiment data, vertical combustion numerical simulation model was built. Vertical burning Simtec numerical simulation method was got by exploring input parameters of the CFD(computational fluid dynamics) simulation software. The simulation results show that burn marks were consistent with the experimental phenomena, and the time function of xb, xp, xp, xp agreed with fitting function based on experiment data. So it can be assumed that Simtec is suitable for simulation of the upward flame spread of thermal thin materials.