Impact of Preheating On Flame Stabilization and NOx Emissions From a Dual Swirl Hydrogen Injector

Abstract Flame stabilization, flame structure, and pollutant emissions are explored experimentally in a swirled injection system using lean air/hydrogen mixtures at atmospheric conditions and moderate Reynolds numbers. The system comprises two coaxial ducts: hydrogen flows through a central channel while air flows through an annular one, both streams being swirled. Two flame stabilization modes, M-shape and V-shape, are identified. Regions of existence for each mode are mapped based on operating conditions. At low air flow rates, the flame is either anchored or lifted depending on the path to the operating condition; at high air flow rates, the flame is always lifted. The influence of air inlet temperature (T = 300 K to 770 K) on stabilization is analyzed. Flame re-attachment is found to be governed by edge flame propagation and well-modeled by preheating effects. Unburnt hydrogen is detected only for global equivalence ratios below 0.4 and at ambient temperatures. NOx emissions decrease with reduced global equivalence ratios and show a decreasing trend as thermal power increases, irrespective of air preheating and flame stabilization regime. At high power, NOx emissions plateau at an asymptotic value. Factors like flame shape, air preheating, and chamber wall heat losses impact on NOx emissions are evaluated. NOx emissions correlate with the adiabatic flame temperature (Tad) and residence time within the combustor.