Impact of Syngas Blending Strategies on NO x Formation Pathways in Ammonia Diffusion Flames

Numerical simulations were performed to examine NOₓ formation in counterflow diffusion flames fueled by ammonia and syngas. The study utilized the Li, Han, and Mei reaction mechanisms to predict flame structure and emissions under varying pressures and compositions. A primary focus was the comparison of three fueling strategies: equimolar replacement of syngas, fixed hydrogen content, and fixed carbon monoxide content. Results show that although increasing the ammonia fraction generally raises NOₓ levels, the specific ratio of H2 to CO significantly alters the emission magnitude. Among the tested methods, maintaining a fixed H2 concentration proved to be the most effective strategy for emission control. Detailed pathway analysis attributes this reduction to the suppression of the thermal NO mechanism, which was identified as the governing route for NO production under all conditions. The study also confirms a linear relationship between oxygen concentration and NO formation. These findings highlight the importance of fuel composition control in the design of cleaner ammonia – syngas combustors.