Fuel interchangeability for premixed combustion in free-flame and porous media burners with hydrogen-enriched natural gas

Co-firing hydrogen and natural gas is one strategy to reduce pollutant emissions from fossil-fuel combustion. This study employed gas interchangeability theory and combustion experiments to determine the maximum hydrogen fraction that can be blended into natural gas for stable premixed combustion in a free-flame (Bunsen burner) and a porous media burner. Delbourg's interchangeability diagram indicates that hydrogen fractions up to 30 vol% remain within gas interchangeability limits, whereas 35 vol% hydrogen exceeds these limits. Experiments under near-stoichiometric conditions showed that up to 26 vol% hydrogen could be blended into natural gas while maintaining stable operation in the free-flame burner; higher hydrogen fractions caused flashback. Additionally, hydrogen blending into natural gas significantly enhanced hydrocarbon combustion in the free-flame burner, resulting in a 33% increase at 26 vol% hydrogen compared to burning pure natural gas. In contrast, porous media burner combustion remained stable with hydrogen enrichment up to 35 vol% across equivalence ratios from 0.2 to 0.8. Both burners showed substantial reductions in carbon dioxide emissions with increased hydrogen concentration. These results suggest that porous media burner technology can potentially overcome conventional limits on fuel interchangeability, offering a viable solution for increased hydrogen integration in combustion applications.