Effects of pressure on instability and cellularity of propagating spherical laminar flames (2nd report, instability wave number of cellular flame)

Cellularity of the propagating spherical laminar flames induced by the flame instability was studied for methane and propane-air mixtures at the equivalence ratios from 0.8 to 1.3 and the initial pressure from 0.10 to 0.50 MPa. The Markstein number was employed to quantify the effects of the equivalence ratio and the pressure of the mixture on the cellularity due to the flame instability. The flame was unstable at the large Peclet number. Cracks due to the flame instability were formed on the flame during the propagation. As the flame propagated, cracks increased and then the flame became cellular. The flame divided by the cracks was stabilized by the increase in the flame stretch. The non-dimensional wave number of the instability increased with the flame propagation. This wave number increased with decreasing the equivalence ratio for the methane mixture and with increasing the equivalence ratio for the propane mixture. It increased with increasing the initial pressure at all the equivalence ratios. It increased as the Markstein number decreased.