Stability and Emissions Characteristics of Syngas and Hydrogen Non-premixed Flames

Hydrogen-enriched syngas produced by biomass gasification is a promising renewable fuel for low-carbon, high-efficiency combustion systems. This study experimentally investigates the stability, flame structure, and pollutant emissions of non-premixed laminar diffusion flames fueled by pure hydrogen and hydrogen-rich syngas mixtures (H 2 /CO and H 2 /CO/CH 4 /CO 2 ). Experiments were conducted using a coaxial burner in a controlled combustion chamber. Flame behavior was characterized by OH* chemiluminescence, flue gas temperature, and CO and NOx emissions. Results show that fuel composition, particularly hydrogen content, strongly influences flame stability and emissions. Hydrogen enrichment enhances flame stability under lean conditions and high air flow rates. Pure hydrogen produces slightly higher NOx emissions (∼20 ppm), whereas H 2 /CO mixtures significantly reduce CO emissions while maintaining low NOx levels (5–8 ppm). Multicomponent H 2 /CO/CH 4 /CO 2 mixtures further decrease CO emissions while keeping NOx nearly constant, demonstrating their potential for clean and efficient biomass-derived syngas combustion.