INTERACTION OF GASLESS AND FILTRATION COMBUSTION

We study the propagation of combustion waves through porous samples in which two reactions occur. The first is a gasless solid-solid reactio n between two solid species in the porous solid matrix to form a solid product, while the second is a solid-gas reaction in which gas delive red to the reaction site through the pores of the sample reacts with o ne of the solid species to form both solid and gaseous products. We co nsider the case of coflow filtration, in which the direction of gas fl ow is the same as the direction of propagation. The gas, consisting of both chemically active and inert components, fitters to the reaction zone through the product region thus transferring heat from the high-t emperature products to the unburned mixture. Using kinetics motivated by large activation energy considerations we determine the structure o f a uniformly propagating combustion wave and, in particular, such imp ortant characteristics as the propagation velocity of the wave, the bu rning temperature and the composition of the product, which is determi ned by the proportion of deficient solid reactant converted in each of the two reactions. We observe that the number of solutions of the gov erning equations varies depending on parameters of the system such as gas mass flux, oxidizer concentration in the gas, kinetic characterist ics of each reaction, etc. Finally, we discuss the superadiabatic effe ct, i.e., how the burning rate is enhanced by coflow filtration, so th at e.g., weakly exothermic gasless systems which would not burn, now d o so due to filtration.