Non-monotonic Cellular Instability of Methanol/Air Flames

Cellular instability of spherical methanol/air flames was investigated in a constant-volume single-chamber cylindrical combustion vessel at initial temperature of 423 K, initial pressure of 1-10 atm and equivalence ratio of 0.7-2.2. The cellular instability on the flame surface was observed at 5-10 atm. Asymptotic analysis was calculated to determine the logarithmic growth rate of cellular instability. The critical Peclet number and critical flame radius were extracted from both experimental observation and asymptotic results. The cellular instability of methanol/air mixtures monotonically increases with initial pressure and non-monotonically varies with equivalence ratio. The non-monotonic flame thickness and monotonic critical Peclet number result in the non-monotonic critical flame radius as well as cellular instability over a wide range of equivalence ratio.