Effects of non-premixed H₂ injection on the stability, shape, and combustion/emissions characteristics of premixed CH₄/air flames: An experimental study

This study investigates the stability and combustion characteristics of a hydrogen-enriched, lean, stratified CH₄/air flame in a model gas-turbine burner that mimics Dual Annular Counter-Rotating Swirl (DACRS) burners in actual aeroderivative gas turbines. The primary CH₄/air mixture was supplied with swirl at the center of combustor, while hydrogen was injected as non-premixed non-swirling jets at the periphery of primary mixture. Enrichment hydrogen was examined for the first time in DACRS-like burners, which highlights the novelty of the present work. The study analyzed the effects of hydrogen fraction (volumetric percentage of hydrogen in the total fuel entering combustor) ranging from 0 to 20% and equivalence ratio ranging from 0.5 to 0.73 on flame stability, structure, and emissions. For the studied combustor, the results showed that the addition of hydrogen in this manner has two opposing effects on the flame. Hydrogen-enrichment enhances the reaction kinetics and flame speed, which should lead to a more stable, brighter, and more compact flame, but the high momentum of the non-swirling hydrogen jets weakens the swirl intensity of the primary CH₄/air flame, which has a negative influence on its stability. The combined net result is that the blowout limit of the flame remained constant at an equivalence ratio of about 0.5, despite increasing the hydrogen fraction up to 20%. NOx emissions were observed not to be affected by hydrogen enrichment up to 20%, but increasing the equivalence ratio favors NOx formation as expected.