Flame Dynamics With Hydrogen Addition at Lean Blowout Limits

Lean premixed combustion is widely used in power generation due to low nitric oxide emissions. Recent interest in syngas requires a better understanding of the role of hydrogen addition on the combustion process. In the present study, the extinction process of hydrogen enriched premixed flames near lean blow out (LBO) in a swirl-stabilized combustor has been examined in both unconfined and confined configurations. High speed images of the flame chemiluminescence are recorded, and a proper orthogonal decomposition (POD) procedure is used to extract the dominant flame dynamics during the LBO process. By examining the POD modes, the spectral information and the statistical properties of POD coefficients, the effect of hydrogen addition on the LBO processes are analyzed and described in the paper. Results show that in unconfined flames, the shear layer mode along with flame rotation with local quenching and reignition is dominant in the methane-only case. For the open hydrogen enriched flames, the extinction times are longer and are linked to the lower minimum ignition energy for hydrogen that facilitates reignition events. In confined methane flames, a conical flame is observed and the POD mode representing the burning in the central recirculation zone appears to be dominant. For the 60% hydrogen enriched flame, a columnar burning pattern is observed and the fluctuation energies are evenly spread across several POD modes making this structure more prone to external disturbances and shorter extinction times.