Observation and regime classification of pulsation patterns in expanding spherical flames

The development of pulsating instability in expanding spherical premixed flames was experimentally studied, leading to the observation and quantification of spiral waves and target patterns over the flame surfaces in rich hydrogen-air, rich hydrogen-oxygen, and lean butane-oxygen-helium mixtures at elevated pressures. The transition boundary to instability was found to agree well with the Sivashinsky criterion, Ze(Le-1)>4(1+3)≈10.9, provided that local values are used in the evaluation of the Zel'dovich number, Ze, and the Lewis number, Le. The similarities to observations on Belousov-Zhabotinsky-reactions are noteworthy, and the present results provide new insights into the appearance order of various reactive-diffusive patterns on the reactive surface while transitioning from the stable domain into the unstable domain.