Dynamics and Stability of Swirl-Stabilized, Non-Premixed CH4/NH3 Combustion

Abstract

Abstract. The rapidly growing global energy demand and concerns over the environmental impact of fossil-fuel-based energy call for the exploration of reliable carbon-free fuels, including hydrogen, ammonia, or blends of both. Despite its great potential as a hydrogen carrier, burning ammonia is not practical due to low laminar flame speed, narrow stabilization limits, and high NOx emissions. This paper aims to study the effect of ammonia addition on the combustion dynamics and stability characteristics of turbulent diffusion CH4/air flames for typical combustion systems. Experiments are conducted using a practical swirl-stabilized burner to investigate the emissions characteristics and the impact of increasing the ammonia content on the flame liftoff height and macrostructure. Results from OH* chemiluminescence indicate stable combustion using fuel blends with up to 35–40% mole fraction, whereas intermittent flame detachments followed by flame root extinction are observed using higher ammonia content of about 60%. Interestingly, a linear relationship is revealed between the maximum achieved liftoff height and the corresponding global equivalence ratio. Emissions measurements with high ammonia content (>60%) reveal NOx emissions lower than those produced with pure methane. Macrostructural analysis with respect to stable methane flame shows that the central recirculation zone with 40% ammonia becomes severely distorted such that its ability in anchoring and stabilizing the flame gets weaker with the increase in the ammonia content.