Non-adiabatic effect on NOx emissions for premixed H2-blended NH3/air combustion under rich-lean-staged conditions

The non-adiabatic effect on NOx emission for the swirl premixed NH₃/H₂/air combustion under fuel-rich/quick-mix/fuel-lean (RQL) conditions was experimentally studied. The wall temperature of the quartz combustor was controlled by surrounding heating. Results showed that both H₂-blending and thermal insulation were in favor of enlarging the low-NOx range and lowering the valley NOx, due to the less NO and unburnt NH₃, and smaller flow rate from the primary stage. In the post-flame zone of the primary stage, increasing combustion temperature significantly enhanced NO reduction, Thus, for low NOx emission, it is essential to keep enough thermal insulation there. Experimental measurements also found remarkable N₂O could be formed in the secondary stage when combustion temperature was low and much unburnt NH₃ was excessive. Kinetic analyses showed this phenomenon was due to the high combination rate of NH and NO, and low reduction rate of H radical.