Experimental and numerical study of flammability limits of gaseous mixtures in porous media

The present work deals with an experimental and numerical study of flammability limits for hydrocarbon–air mixtures in porous media and their dependence on the physical and geometrical properties of the solid phase. Experimental data have been obtained in a standard flammability apparatus modified through the insertion of a packed bed of spheres. Numerical data have been obtained through integration of the equations of a one-dimensional model with single step kinetics. The model accounts for heat transfer to the solid phase in the porous medium. The kinetic parameters of the model are tuned in order to match flammability limits for freely propagating deflagrations; then, the model is applied to cases with porous medium. Numerical results are compared with experimental results and at least qualitative agreement is found. Particularly, both sets of data show that flammability limits are more sensitive to the geometric properties of the porous medium than to its physical properties. An explanation is given through the analysis of the heat transfer process. The results show that, in modelling flammability limits within porous media, heat losses to the solid phase should be taken into account, along with fluid-dynamic effects, to correctly understand extinction mechanisms and predict flammability data.