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Abstract
A numerical model of non-adiabatic flame propagation is used to examine the dynamic properties of premixed flames in mixtures near flammability limits in planar and spherical geometries. Using highly schematic thermodynamic, chemical and transport models, numerical results are found to be, in the limit of high activation energy, in good agreement with analytical solutions. With more detailed models representative of lean methane-air mixtures experiencing heat loss from CO2 and H2O band radiation, numerical results for spherical geometry are found to be in very good qualitative and good quantitative agreement with results obtained in microgravity (μm) experiments. In particular, experimentally observed memory effects associated with the ignition process are reproduced. It is concluded that flame dynamics and extinguishment processes at μg are probably a result of the interactions of the Lewis number effect, flame front curvature and heat loss due to gas radiation.