An experimental study and numerical simulation of flame spread over surface of PMMA slab

Introduction. Polymer materials are widely used, however the actual object is to provide polymers combustion ­model to predict their behavior under fire, and reducing flammability. The work is devoted to the experimental ­study and numerical simulation of flame propagation over the surface of horizontally and vertically placed slabs of polymer in still air.
Methods. The object of the investigation was cast polymethylmethacrylate (PMMA). The experiment was focused on measurement of the spatial distributions of the temperature and species concentrations of the PMMA pyrolysis and combustion products in the gas-phase over the surface of PMMA. Temperature was measured by micro­thermocouple with diameter of 50 microns. Probe mass-spectrometry was used for the measurement of the spa­tial distribution of species concentrations in the flame.
Results and discussion. The main species (mehylmethacrylate (MMA), O2, CO2, H2O, N2, C2H4 (ethylene), C3H6 (propylene)) were identified and their concentration profiles were measured on the different distance from the flame front. The chemical structure of the flame was established to be in good agreement with the thermal one. The size of the “dark zone” of the flame, in which the temperature near the surface of the polymer is minimal, correlated well with the size of the oxygen-free zone. The mass burning rate, the velocity of flame propagation, the width of the pyrolysis zone and the temperature distribution in the condensed phase were also measured. Based on the experimental results, densities of conductive and radiation heat fluxes from the flame to the fuel surface were deter­mined. Calcula­tion of the radiation heat flux density was carried out under the assumption of an optically thin ­model. Modeling of the horizontal flame propagation over the PMMA surface was carried out using a two-dimen­sional conjugated laminar combustion model that takes into account one-step reactions — the decomposition reaction of PMMA in the condensed phase and the oxidation of decomposition products in the gas phase. Modeling of the vertical flame propagation over the PMMA surface was carried out using economical model of FDS.
Conclusion. The model was shown to describe satisfactorily the experimental data such as the mass burning rate, flame propagation velocity, as well as the temperature distribution and concentration of species near the flame front.

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