Research on flame anchoring mechanisms of annular jet micro-mixing flames for hydrogen-containing syngas

Annular jet micro-mixing (MM) nozzles, due to the presence of central recirculation zones (CRZs), outer recirculation zones among the nozzles (ORZs), and flame interaction zones (FIZs), have greater potential than the circular nozzles in maintaining flame stability when facing the frequent changes in operating conditions of gas turbines. This study focused on the annular jet MM nozzles using syngas. At the different equivalence ratio (Φ) and air velocity at the nozzle inlet (u_air), this study introduced a dimensionless parameter C (the relative contribution ratio of the CRZ) to quantify the contributions of dual recirculation zones to flame anchoring through simulations. Then the effects of the FIZ on flame anchoring and the pollutant emissions of the nozzles were investigated through experiments using hydroxyl planar laser-induced fluorescence. The results show that as Φ or u_air increases, C rises by 70% and 152%, respectively. At u_air = 101.0 m/s, C is approximately 50%, indicating the role of the CRZ in flame anchoring becomes increasingly important, even comparable to that of the ORZ. The flame interaction enables flame anchoring in the ORZ under all conditions. As Φ or u_air increases, the relative area of the FIZ increases by 57% and 131%, respectively. The enhanced flame interaction also promotes flame anchoring in the CRZ. When Φ exceeds 0.438 or u_air surpasses 67.4 m/s, carbon monoxide emission drops below 5 μL/L (@15% O₂). Nitric oxide emission maintains below 8 μL/L (@15% O₂) in all conditions.