Experimental Study and Numerical Modeling of Downward Flame Spread Along a Single Pine Needle: Part 1 (Experiments)

This work presents an experimental study of downward flame spread over a vertically positioned single pine needle of Pinus Sibirica. Detailed spatial measurements in the gas phase have been carried out to determine the chemical and thermal flame structure of the spreading flame. In addition, temperature distribution in pine needle is also measured. In the gas phase micro thermocouple measurements were used to determine temperature distribution; mass spectrometry with microprobe sampling was used to measure the concentration profiles of О2 and the main combustion products (СО2, СО, Н2О). The micro thermocouple method was also used to measure temperature distribution in a pine needle for flame spread along it. The data obtained from the experiments on single vertical pine needles reveals two stages in downward flame propagation: (1) a zone in the vicinity of the leading edge of the spreading flame where virgin pine needle decomposes to form char and volatile pyrolysis products formed. The pyrolysis products mix with air and ignited by flame behind causes flame to propagate; and (2) a zone where heterogeneous burning of char occurs. The downward flame spread velocity along a single pine needle was also measured for several counter-flow air velocities to obtain dependence of flame spread rate on counter-flow velocity. The data obtained in this work can also serve as a much needed base for testing and refining the numerical models describing flame spread along individual components of forest fuels (FF). Further, as the flame propagation along a bed of FF is similar to that along charring polymer materials, the data obtained and the applied methods of research may be also of interest to those studying the charring polymer combustion mechanism.