Fast and slow modes of the propagation of the combustion front in heterogeneous systems

Experimental results are presented in favor of the existence of fast and slow modes of the propagation of the combustion front in diluted heterogeneous mixtures of reactive particles. A theoretical combustion model is proposed to explain the existence of these modes. The transition from the fast to the slow mode, which occurs in a narrow range of the degree of dilution of the mixture by inert powder, is associated with the break of a percolation cluster formed by reagent particles that are in direct contact with each other. After such a break of the cluster, the thermal energy of combusting particles is still insufficient to maintain the combustion wave. A sharp decrease in the front velocity in this case is associated with the necessity of heating inert regions inevitably appearing in its path.