PROPAGATION OF PREMIXED GASEOUS EXPLOSION FLAMES IN POROUS-MEDIA

Flame propagation velocities have been measured for methane-air and propane-air mixtures in four kinds of porous medium, with varying initial parameters such as pressure (from 0.06 to 2.5 MPa), equivalence ratios (0.70-1.65), and the characteristic size of cavity space (1.15-4.5 mm). All the data are well correlated by the general dependence Re = c . Pe3, where Re is the Reynolds number based on the difference between flame propagation speed, S, and laminar burning velocity, S(u), Pe is the Peclet number based on S(u), and c is an experimental constant. The dependence may be derived theoretically based on two assumptions: (1) the flame propagation velocity in turbulent moving gas is determined by the maximum flow pulsation V(m), S = V(m) + S(u); and (2) at increasing values of V(m), greater heat losses from the flame front into the porous medium occur until, finally, the flame is quenched. Some deviations from the general dependence observed for rich propane mixtures are explained by the manifestation of thermal-diffusive instabilities that are controlled by the Lewis number and neglected in a theoretical model.