Laminar Burning Velocities and Emissions of Hydrogen-Methane-Air-Steam Mixtures

Humidified gas turbines using steam generated from excess heat feature increased cycle efficiencies. Injecting the steam into the combustor reduces NOx emissions, flame temperatures, and burning velocities, promising a clean and stable combustion of highly reactive fuels such as hydrogen or hydrogen-methane blends. This study presents laminar burning velocities for methane and hydrogen-enriched methane (10 mol. % and 50 mol. %) at steam contents up to 30% of the air mass flow. Experiments were conducted on prismatic Bunsen flames stabilized on a slot-burner, employing OH planar laser-induced fluorescence (OH-PLIF) as an indicator for flame front areas. The experimental burning velocities agree well with results from one-dimensional simulations using the GRI 3.0 mechanism. Burning velocities reduce nonlinearly with ascending steam mole fractions and more rapid compared to simulations using "virtual H2O" stemming from a chemical influence on reactions. Hydrogen enrichment increases burning velocities, extending the flammability range toward leaner and more humid mixtures. Additionally, measured NOx and CO emissions reveal a strong reduction in NOx emissions for increasing steam dilution rates, whereas CO curves are shifted toward higher equivalence ratios.