## 4 Conclusions  
In this study, the effects of ammonia ratio, excess air coefficient, temperature, residence time, and gas concentration on NO generation during the combustion of NH\({}_{3}\)/CH\({}_{4}\) and NH\({}_{3}\)/CO were investigated. The main conclusions are as follows:  
1. When the excess air coefficient \(\alpha\geq 1\), with the increase in the proportion of ammonia in the fuel gas, the production of NO increased first and then decreased. When the proportion of ammonia in NH\({}_{3}\)/CH\({}_{4}\) was 40% or 50% in NH\({}_{3}\)/CO, the production of NO reached the maximum value. However, when the excess air coefficient \(\alpha<1\), the NO production gradually decreased with the increase in ammonia proportion. The NO emissions of the blended fuel were higher than that of pure ammonia. Figure 11: NO production of NH\({}_{3}\)/CO co-firing under different fuel gas concentrations at 1500 \({}^{\circ}\)C.  
Figure 10: NO produced by NH\({}_{3}\)/CO combustion at different residence times at 1500 \({}^{\circ}\)C.  
2. When the excess air coefficient \(\alpha\) was in the range of 0.9-1.1, the emission of NO from combustion increased with the increase in the excess air coefficient, but the excess air coefficient had little effect on the NO production when \(\alpha\geq 1\), and the NO production when \(\alpha<1\) was at a very low level when NH\({}_{3}\)/CH\({}_{4}\) was mixed. 3. In the range of 900-1500 \({}^{\circ}\)C, the amount of NO produced by mixed gas combustion gradually decreased with the increase in temperature, and the degree of influence of temperature on the amount of NO production gradually weakened with the increase in temperature. 4. The amount of NO produced by combustion gradually decreased with the increase in residence time, and, according to the change trend of the amount of NO, when the residence time was long enough, the NO content in the flue gas was in a stable state. The increase in residence time was associated with the decrease in NO production, and the effect of residence time on NO production was gradually weakened with the increase in residence time. 5. The concentration of fuel gas in the mixture had a large influence on the generation of fuel NO\({}_{x}\). When the excess air coefficient \(\alpha\geq 1\), the amount of NO produced by combustion also increased with the increase in the fuel concentration, and the influence of the concentration was also enhanced with the increase in the excess air coefficient. However, when the excess air coefficient \(\alpha<1\) increased the fuel concentration, NO production decreased. Based on the analysis of experimental results and comparison with other literature, we believe that these results can be extrapolated to different combustion scenarios or fuels. These findings have potential implications for optimizing combustion processes in terms of NO emission control. With suitable conditions, the fuel ammonia combustion can be controlled and produce lower NO emissions. For example, the excess air coefficient should not be too high, and the residence time should not be too short. The NO\({}_{x}\) formation characteristics of ammonia combustion mixed with methane or carbon monoxide was studied in this paper. This will help guide the clean and efficient utilization of ammonia, which is a new renewable energy source, and which can turn industrial by-products into wealth. Based on the insights gained from this paper, the key area of future research should be how to improve the combustion efficiency of ammonia and reduce NO emissions by mixing industrial byproducts such as blast furnace gas or low calorific value gas while reducing the cost, so as to achieve complementary advantages. Conceptualization, Y.D. (Yongbo Du) and C.W. ; formal analysis, S.Z., C.W. and Y.W. ; funding acquisition, Y.D. (Yongbo Du); investigation, S.Z. and Y.W. ; project administration, Y.D. (Yongbo Du); supervision, Q.L., Y.D. (Yaodong Da) and D.C.; writing--original draft, Y.D. (Yongbo Du) and S.Z. ; writing--review and editing, Y.D. ([PERSON]), Q.L., Y.D.