Downward burning of PMMA cylinders: The effect of pressure and oxygen

Better understanding the burning behavior of solid fuels is necessary in order to be able to estimate more accurately the fire risk that they might represent. The burning rate is an essential component when assessing the growth of a fire, since it determines the heat released during the fuel burning. The objective of the present work is to study the effect of ambient pressure and oxygen concentration on the burning of cylindrical samples of polymethyl-methacrylate (PMMA) in opposed flow flame spread conditions. Experiments are conducted using pressures ranging between 100 and 30 kPa and oxygen concentrations between 19% and 23%, with a forced flow velocity of 100 mm/s. The experimental conditions reflect environments potentially encountered in future spacecraft cabins. The data collected show that during downward opposed flame spread the surface regression rate, and consequently the mass burning rate, decreases with decreasing ambient pressure and increases with decreasing oxygen concentration. The data presented is correlated with a simplified model to estimate the surface regression rate based on the mixed heat convection coefficient and the B number. Model predictions are made based on fuel properties as well as the relevant environmental conditions. The predictions of the model agree well capturing the effect of ambient pressure and oxygen concentration. The correlations provide information about the variations in the burning rate in environments with variable pressure and oxygen concentration, providing guidance for potential for fire safety testing and design in different ambient conditions.