Lean premixed combustion is widely used to achieve better compromise between nitric oxide (NOx) emissions and combustion efficiency (related to CO levels). However, combustor operation near the lean blowout (LBO) limit can render the flame unstable and lead to oscillations, flashback or extinction, thereby limiting the potential of lean combustion application. Recent interest in integrated gasification combined cycle plants (IGCC) and syngas combustion requires an improved understanding of the role of hydrogen on the combustion process. Therefore, in the present study, combustion of pure methane and blended methane-hydrogen with hydrogen-levels up to 80% by volume has been conducted in a swirl stabilized premixed combustor. Stereo particle image velocimetry (PIV) and OH* chemiluminescence imaging have been used in this study. Results show that there is a single-ringed structure of internal recirculation zone (IRZ) in the non-reacting flow, while in the reacting flows there is a complicated flow pattern with a two-celled IRZ structure in which the axial velocity near the center-axis is oriented downstream. As equivalence ratio decreases, the width of IRZ decreases in methane flames while it increases in hydrogen enriched flames, and the flame shape changes from conical to an elongated columnar shape, especially in hydrogen enriched flames. There are two different modes of vortex breakdown observed, spiral mode in methane flames and bubble mode in hydrogen enriched flames. The mechanisms of LBO in pure methane and hydrogen enriched premixed flames are shown to be different and explained in the present study.

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