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,...