A comparison of the characteristics of disk stabilized lean propane flames operated under premixed or stratified inlet mixture conditions

The work investigates some of the differences and similarities between fully-premixed and stratified lean propane flames stabilized in an axisymmetric bluff-body swirl burner configuration. In this arrangement a double-cavity propane-air premixer, formed along three concentric disks, supplies the afterbody disk recirculation region with a regulated radial equivalence ratio gradient. Flame stabilization can be established at a range of co-flow swirl intensities under, either uniformly premixed or stratified inlet mixture conditions. Measurements of turbulent velocities, temperatures, chemiluminescence imaging of OH* and CH* and gas analysis provided information for lean and close to blow-off flame configurations. Supporting Large Eddy Simulations were undertaken with the Thickened Flame Model and a nine-step mechanism for propane combustion to complement the experiments. The combined methodology helped to elucidate some of the parametric characteristics of the diverse flame topologies obtained in the above burner. The performance of the adopted turbulent chemistry closure and the reduced chemical scheme in addressing the effect of mixture heterogeneities on the flame anchoring and structure of the studied configurations is also evaluated. The interaction of the toroidal flame fronts with the recirculation stabilization region, the impact of heat release on the development of the axisymmetric wakes and the flame front disposition at ultra-lean and close to blow-off operation are presented and discussed for the different fuel-air inlet mixture profiles.