Experimental study of flame dynamics and NOx emission characteristics in a NH3-H2 blended non-premixed swirl combustor

Ammonia (NH3), with its zero-carbon potential, is a promising green hydrogen carrier and alternative energy source. However, its limited reactivity and high activation energy pose combustion challenges, which blending with hydrogen (H-2) in swirl burners can be effectively mitigated. This study establishes a swirl model burner and employs ICCD (Intensified Charge-Coupled Device) and OH-PLIF (Planar Laser-Induced Fluorescence) to investigate NH3-H-2 blended non-premixed diffusion flame dynamics across at varying hydrogen blending ratios (X-H2 = 0.1-0.5) and equivalence ratios (& Oslash; = 0.6-1.3). Insights into the characteristics of NOx emissions are gained through gas analyzer. It is found that the flame stability can be enhanced by increasing the equivalence ratio in operational range. Flame instability initially increases and then decreases with rising X-H2, peaking at X-H2 = 0.3 and & Oslash; = 0.8; however, when & Oslash;>1.0, it negatively correlates with hydrogen blending ratios. Beyond this point, additional hydrogen blending significantly improves stability and transitions the flame shape from 'M'-shaped to coronal-conical. Additionally, elevated X-H2 enhance OH radical fluorescence, indicating a more intense flame reaction. Notably, NOx emissions peak between & Oslash; = 0.7-0.8, followed by a rapid decrease and a slight increase at & Oslash;>1.0. These emissions exhibit a positive correlation with hydrogen blending in lean-burn and a negative correlation in rich-burn, closely aligning with trends in flame stability. Elevated NOx emissions are consistently observed under unstable flame conditions, particularly near extinction boundaries, where NOx levels exhibit abrupt variations. Additionally, the influence of turbulence intensity on NOx emissions in non-premixed turbulent combustion within swirl combustors requires further research.