A double-annulus counter-rotating premixed swirl burner was utilised to investigate the effect of varied air flow and equivalence ratio between the inner and outer annulus on the flame structure and emission performance. The air and methane gaseous fuel for each annulus were independently premixed at the plenum prior to combustion at atmospheric condition. Imaging of OH* chemiluminescence was performed to obtain the flame structure of stratified flames. Higher swirl flow for richer mixture in the inner annulus generates an elongated and enlarged area of flame reaction zone due to increased flame intensity. Emission measurements show the arrangement of leaner inner/outer richer premixed air/fuel produce emissions comparable to baseline case of homogenous mixture and flow. Under the arrangement of stratified mixture of richer inner/leaner outer annulus, significant higher emissions of CO, NO and NO2 were shown. Variation of the air flow split ratio between the annuluses affects emissions, in particular, higher inner/lower outer swirl flow arrangement results in higher emission rates under rich inner/lean outer mixture stratification.
