Stability and Emission Characteristics of a Stratified Hydrogen-Enriched Oxy-Methane Flame on a Multihole Burner: An Experimental Study.

Hydrogen (H) enrichment is a viable solution to deter the early blowout of oxy-fuel flames at high CO dilution levels and to enhance combustor turndown in the supercritical-CO cycles of zero-emission power plants. This was already implemented successfully in a previous study by the author, where H was premixed with the oxy-reactants upstream of the burner headend in a fully premixed flame stabilized on a micromixer-like burner. The micromixer technology is known for its superior flame stability and inherent fuel/oxidizer flexibility. To avoid the higher risk of flashback when H is premixed with the primary reactants, the present study introduces the enrichment H in a nonpremixed manner from the enhanced-blowout fuel circuit of the micromixer burner, which comprises circumferential jets that surround the core oxy-flame. This approach aims to enhance combustor turndown even further by benefiting from inducing stratification in the flame. It was found that the blowout limit of the fully premixed (CH/H/O/CO) flame did not improve by stratification (H-CH/O/CO); it deteriorated slightly. The present study thus analyzes the stability, morphology, and CO emissions of the stratified flame, in order to explain this behavior and provide recommendations for how hydrogen enrichment should be introduced in oxy-fuel micromixer combustors.