Unsteady modes of filtration combustion

Unsteady modes of filtration combustion are studied with the use of a three-dimensional mathematical model. The model describes exothermic chemical interaction of condensed systems with active gases and formation of solid products. Unsteadiness of the filtration combustion modes is caused by instability of the plane combustion front. Formation of the periodic structure of the front of combustion of porous cylindrical samples with different cross-sectional shapes is studied. It is demonstrated that different periodic regimes of combustion-front propagation can occur under conditions of instability of the plane combustion front and deficit of the active gas mass inside the pores, depending on the cross-sectional shape of cylindrical samples and various methods of heat and mass transfer between the sample and the ambient gas medium. Periodic regimes of oscillatory (volume and surface) combustion for samples with a circular cross section, spinning mode for samples with a ring-shaped cross section, and complicated periodic regimes for samples with a rectangular cross section are obtained.