| Summary: | Ammonia is an ideal renewable, carbon-free fuel and hydrogen carrier, which produces nitrogen and water after complete combustion in the presence of oxygen. However, ammonia has low reactivity, slow flame-propagation speed, and carries risks of high nitrogen oxide (NO<i><sub>x</sub></i>) emissions. Co-firing ammonia with an industrial by-product gas (with CH<sub>4</sub> and CO being the main combustible materials) is a cost-effective and convenient method of improving the combustion characteristics of ammonia, but attention still needs to be paid to the NO<i><sub>x</sub></i> generation. Currently, the research on NO<i><sub>x</sub></i> formation during co-firing of ammonia with other fuel gases is still insufficient. In this study, a high-temperature furnace reaction system was used to investigate the NO<i><sub>x</sub></i> formation and inhibition mechanisms during the combustion of NH<sub>3</sub>/CH<sub>4</sub> and NH<sub>3</sub>/CO mixtures. By varying the ammonia blending ratio, excess air coefficient (<i>α</i>), temperature, residence time, and fuel concentration, the key factors influencing NO<i><sub>x</sub></i> generation and inhibition were further analyzed. The results showed that when <i>α</i> was no less than 1, the production of NO<i><sub>x</sub></i> initially increased and then decreased with an increasing proportion of ammonia in the fuel gas. Within the temperature range of 900 °C to 1500 °C, the amount of NO<i><sub>x</sub></i> generated during the combustion of the mixed gas gradually decreased with the increase in temperature. Under the conditions of NH<sub>3</sub>/CH<sub>4</sub> and NH<sub>3</sub>/CO, the emissions of NO<i><sub>x</sub></i> were higher than those during pure ammonia combustion.
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