Experimental study on characteristics of flame spread over inclined wood Sheets

The present paper is aimed at introducing its experimental research of the flame spreading mechanism over charring materials facing the orientation under the natural convection in the direction of gravity assistance. In this research we have chosen wood sheets as typical charring materials while the burning process was observed at an angle of orientation α from 20° to 90° (, i.e. a vertically upward burning). Data the paper has adopted are taken to show the flame spreading characteristics of thermodynamically thick-enough charring materials. Thus we have found that the flame behavior over the solid surface may go through such states as extinguishment after removing the igniter, steady burning, accelerated burning and full burning similar to the flash with the constantly increasing burning angle. But the local flame spreading rate actually fluctuates increasingly with the angle. And when the flame spreading behaviors for the sample thickness d=2mm is compared to that for the sample thickness d=3mm, it can be found that the thinner the sample is the more sensitive to the angle change. The flame parameters such as the flame angle θ, flame length L can be measured for the sample thickness d=3mm. The above parameters also contribute to the deduction of the calculated flame spreading rates, which can be compared with the experimental results. In the range of 0°α60°, the predicted flame spreading rates prove to be in well conformity with the experimental flame spreading rates, but in the range of α≥60°, the discrepancy is also to be noted. Measurements of the temperature distribution on the upper and rear surfaces of the samples have also been carried out by using the fine thermocouples. Based on the temperature data, the contributory factors of the flames over both up and rear surface to the flame spreading behavior are also discussed here in the paper. For α30°, the flame over the ear-surface is predominant for the whole burning process and the flame over up-surface is predominant just for α≥30°.