Filtration combustion of lean methane-air mixtures in inert, high-porosity micro-fibrous media was studied experimentally in quartz tubes with different diameters. First, an overall stability diagram was obtained. Between the upstream and downstream propagating regimes, a specific rigid standing wave regime was observed, whereas only one standing wave point existed in other ordinary porous media. A specific instability phenomenon of a combustion wave splitting into two or more parts during wave propagation downstream was also observed in smaller diameter tubes at high filtration velocities. In principle, the results of a conventional two-temperature 1D analytical model captured the main feature of the process obtained in the experiment, but failed to explain the process of flame anchoring to the porous carcass that was observed under variation of the mass flow rate. The possible causes of the failure of the conventional modeling approach were presented.

Dynamical behaviour of the premixed flame propagating in the inert high-porosity micro-fibrous porous media has been studied numerically. Effects of mixture filtration velocity, equivalence ratio and burner transverse size on the flame structure have been investigated and the regions of existence of different combustion regimes have been determined. It was found that the influence of the hydrodynamic instability on the flame dynamics is significant in the case of the moderate and high filtration velocities and this effect is negligible at the low velocities. At the moderate filtration velocities the effect of hydrodynamic instability manifests in the flame front deformation and in particular in the flame inclination. It was found that the flame can be stabilized within the whole interval of the filtration gas velocity, whereas in the ordinary porous media the standing wave is settled only at fixed value of gas filtration velocity. This finding is in line with recent experimental results on combustion in micro-fibrous porous media (Yang et al., Combust. Sci. Tech. 181 (2009), 1–16). Possible physical interpretation of the flame anchoring effect may be given on the base of present numerical analysis. At the high filtration velocities the hydrodynamic instability manifests itself in periodical appearance of the moving wrinkles on the flame front surface which forms non stationary high temperature trailing spots behind the leading part of the flame front. Such dynamics may be associated with splitting wave structures which were revealed in previous experiments (Yang et al., Combust. Sci. Tech. 181 (2009), 1–16).