An experimental study of horizontal flame spread over PMMA surface in still air

The paper presents a comprehensive experimental study of flame spread over the surface of horizontally placed slabs of four types of PMMA specimens in still air. Temperature distributions in the gas phase near the solid fuel surface and in the condensed phase were measured using microthermocouples. Spatial variation of the species concentration in the gas-phase flame near the solid fuel surface was measured using probing mass spectrometry. Also flame spread rate over the polymer surface was measured. The experiments revealed differences in the combustion character of the specimens investigated. At the flame spread over surface of two (out of the four) specimens boiling and formation of large bubbles were discovered. The main flame components including ММА, О2, СО2, Н2О, N2, С2Н4 (ethylene), С3Н6 (propylene) have been first identified, and their concentration profiles at different distances from the flame front have been measured. The data on the chemical flame structure have been shown to be in good agreement with the data on its thermal flame structure. The size of the “dark zone” of the flame, in which the temperature near the polymer surface is minimal, correlates well with the size of the oxygen-free zone, which is adjacent to the burning surface. Conductive heat feedback from the flames to the condensed fuel surface was estimated on the basis of the experimental results. The conductive heat flux averaged over the burning surface was estimated to be approximately 13.2 kW/m2. It has been established that it is maximal in the flame front and decreases as the specimen burns out. The data obtained may be used for developing and validating a numerical model of flame spread over PMMA surface.