Pore-scale flame dynamics in a one-layer porous burner

Abstract

Novel design of one-layer porous burner for experimental studies of the flame front dynamics at pore scale level is proposed. Results of the experimental and numerical studies of non-stationary flame front behavior at pore scale are discussed and compared at a qualitative level. The results demonstrate that upstream propagation of the combustion wave can be accompanied by the oscillations of two different types. The first type is the FREI-like pulsations, which mechanism is identical to the flames with repetitive extinction and ignition in narrow channels with external heating. The second type is the small-amplitude oscillations, which, apparently, have the same nature as the transitional oscillatory combustion mode between the steady flame and fully-developed FREI pulsations. This type of unstable flame behavior differs by existing of the flame over the entire oscillation period without extinction. It is found that these two types of flame oscillations clearly separates by oscillation frequencies and amplitudes. Typical frequencies of FREI-like pulsations are about tens of hertz, while for small amplitude oscillations it has an order of hundreds of hertz. It was shown that both types of oscillations can coexist inside the porous media at the same time but at different pore channels. Moreover, the mixed oscillations representing by fully developed FREI-like pulsations alternating with small-amplitude oscillations are frequently observed.