The effects of tortuosity and dispersion on porous combustion

In this paper, the porous flow effects (tortuosity and dispersion) on the characteristics of porous combustion are numerically studied. The effects of tortuosity and dispersion are introduced in the porous diffusion coefficients to investigate the influences on the flame propagation speed and the operating range of inlet flow velocity. It is found that the ratio of thermal to mass diffusion coefficients (Le p = α L /D L ) due to the features of porous flow can drastically affect the flame propagation speed, which is similar to the effect of the Lewis number on the flame speed in free stream. Consequently, the results show that the operating range of inlet flow velocity (U max -U min ) for a two-section burner can be greatly altered by the tortuosity and dispersion effects in the two porous solids. To decrease Le p or decrease both α L and D L with constant Le p in the upstream section can significantly extend the operating range by decreasing U min ; on the other hand, to increase Le p or increase both α L and D L with constant Le p can also remarkably extend the operating range by increasing U max . Moreover, it is possible that the tortuosity effect in the upstream section (small pore) may greatly alter U min ; while the dispersion effect in the downstream section (large pore) can dominate U max .