## 4 Results and Discussions
### Laminar Burning Velocity of Binary Fuel Blending
The Shrestha model [31] accurately predicts \(\mathrm{\SI{L}}\) on the lean side of stoichiometry, while it overpredicts it on the rich side. The Li model, however, demonstrates good predictions of \(\mathrm{\SI{S}_{l}}\) for all hydrogen blends. **For NH\({}_{3}\)/CH\({}_{4}\)/air flames**, the laminar burning velocities of ammonia blended with methane at concentrations of 20%, 40%, 60%, and 80% are represented by the red color in Figures 3, 4C and 5A-D, respectively. These figures depict the laminar burning velocities as a function of equivalence ratios, where the ternary mixture contains 0% hydrogen fraction. The current experimental results demonstrate higher consistency with the literature data [19; 26]. Figure 5: The LBV of ternary fuel–air flames are shown as percentages relative to different equivalence ratios at 0.1 MPa and 298 K. The fuel compositions for each case are as follows:(**A**) 20% NH\({}_{3}\)/80%CH\({}_{4}\); (**B**) 40% NH\({}_{3}\)/60%CH\({}_{4}\); (**C**) 60% NH\({}_{3}\)/40%CH\({}_{4}\); (**D**) 80% NH\({}_{3}\)/20% CH\({}_{4}\) for different H\({}_{2}\) blends. Furthermore, excellent consistency is shown between the experimental and predicted data from the Okafor [20] and Li [33] models, particularly in terms of predicting the laminar burning velocity (S\({}_{I}\)) values. Larger discrepancies can be observed for the Shrestha model data compared to the results of the other models, particularly on the rich side of the equivalence ratio. The Shrestha model shows good agreement with the experimental data in general for lean and stoichiometric conditions and higher ammonia fractions, while the Li model outperforms the Shrestha model on the rich side. Remarkable agreement, especially noticeable for \(\phi\) = 0.8, can be observed between the Okafor model and the experimental results. The three models demonstrate good performance throughout the range of the 20% ammonia blend, as methane already plays a dominant role in the combustion process. It is worth noting that the value of the equivalence ratio at which the maximum SL occurs remains constant at 1.05, regardless of the number of methane blends, for mixtures without any hydrogen blend. This behavior is clearly different from NH\({}_{3}\) and H\({}_{2}\) mixtures, as discussed previously. The primary reason for the underestimation of the Li model [33] and Okafor model [20] is the dependency on the Tian model [22]. The HCO \(\rightarrow\) CO conversion pathway may be highly affected by the underestimation of LBV. HCO facilitates H radical production in the forward reaction HCO = CO + H and promotes the propagation of chain reactions, While HCO + H = CO + H\({}_{2}\) atom transfer reactions have a chain-terminating character. In methane-ammonia flames, the reactions that take place between amine radicals and their products become more noticeable as the mixtures become richer, as does the impact on the burning [20]. **For H\({}_{2}\)/CH\({}_{4}\)/air flames**, the laminar burning velocities of methane with 0%, 20%, and 40% hydrogen blends are shown in Figure 4A. It can be observed that increasing the hydrogen blending leads to an increase in the LBV of the mixture, and the maximum S\({}_{I}\) is shifted to the rich side of stoichiometry as the hydrogen blend increases. The predicted LBV for pure methane agrees well with the experimental data using different models. Regarding the hydrogen addition of 20%, the predicted data exhibit a similar trend, with an underestimation in the lean and stoichiometric regions and an over-prediction for the rich side. However, for the 40% hydrogen addition, significant discrepancies can be observed. The Li [33] and Okafor [20] models underpredict the LBV of all equivalence ratios, while the Shrestha model [31] demonstrates good agreement with the experimental results. The LBV grows non-linearly with increasing hydrogen concentration, and the discrepancies become more significant for mixtures with higher hydrogen concentrations.