Ignition of porous bodies under conditions of counterflow nonstationary filtration of a gas

An analytical method for calculating the time characteristics of ignition of a porous body with outflow of an inert gas from the sample (counterflow nonstationary filtration) is developed employing the wave theory of ignition and an averaging technique using a certain weighting function. Numerical calculations confirmed the validity of the main assumptions of the theory on the stagewise nature of the ignition process and the wave mechanism of heating of the material. Complete qualitative and good quantitative agreement between conclusions of an approximate analysis and numerical results is shown. The error in determining the times of establishment of zero gradient and disturbance of temperature equilibrium does not exceed 50%. It is established that the equations of isothermal filtration are adequate for describing the process of gas escape from a porous body during ignition. It is shown that the gas mass flow can be calculated using a quasistationary approach. The region of applicability of the model of a semiinfinite body in ignition problems with counterflow nonstationary filtration of gases is determined.