Pressure drop in a porous layer during combustion

In porous matter layer combustion a manometer connected with the cold charge end registers pressure drop in the layer depth. This pressure drop has been discovered more 20 years ago but up to now has not been explained. Here is experimentally shown that this effect is analogous to pressure change in pores in diffusion of a light gas (helium, hydrogen) from them (or into the) in the isothermic conditions and is enhanced in combustion mainly owing to a cocurrent flow of the Stephan type as well as due to thermal diffusion. Probably the pressure decrease in a flame following from the Guogonio adiabat theory favours pressure drops in pores.