## 4 Results and Discussions
### Laminar Burning Velocity of Ternary Fuel Blending
The second trend observed is that, as the hydrogen blending increases by 0%, 20%, and 40%, the enhancement parameter for the rich side of the stoichiometric condition also increases, surpassing the enhancement at stoichiometry for 40% hydrogen blending. This behavior arises because hydrogen becomes the dominant fuel in the mixture. These experimental values demonstrate the high potential of these fuel blends to enhance the LBV of ammonia/air flames when used in the appropriate blending ratios. This understanding is crucial for the future industrial application of ammonia combustion. The other parameter is the normalized experimental LBV \(S_{l}^{*}\), identified by the following equation:  
\[S_{l(\gamma,\beta,\sigma,\Phi)}=\frac{S_{l,M}(\gamma,\beta,\sigma,\Phi)}{S_{l, CH_{4}}(\Phi)} \tag{8}\]  
where \(S_{l,CH_{4}}(\Phi)\) is the LBV of the neat methane-air mixture that depends only on the equivalence ratio against the ammonia blending ratio for different hydrogen blends at an initial pressure of 0.1 MPa and initial temperature of 298 K. This parameter shows the blending effect related to the LBV of methane with respect to dual blending (ammonia and methane) and ternary blends (ammonia, hydrogen, and methane). Figure 8 demonstrates the normalized LBV versus ammonia blends for 0, 20, and 40% hydrogen blends for a range of different equivalences ratios. The figure provides information on the influence of the ternary fuel effect that increases the LBV of 40% hydrogen starting from 75% to 160% of LBV of methane. For example, the influence of hydrogen addition to the ammonia-methane mixture on LBV can be achieved in the LBV of methane at an equivalence ratio of 1.2 by using 20% hydrogen, 64% methane, and 16% ammonia, or 40% hydrogen, 15% methane, and 45% ammonia. When the ammonia ratio is increased, there is a significant drop in the normalized velocity for zero hydrogen blends, especially for zero hydrogen blends. Nevertheless, \(S_{l}\) decreases only significantly with the increasing ammonia ratio. When the hydrogen ratio increases, \(S_{l}\) begins to grow noticeably for all equivalences ratios. It can be seen from the figure that the effect of hydrogen blending not only increases the laminar flame speed but also tends to the rich side to be maximized. To further demonstrate the effect of ternary fuel blending on the accuracy of the three models, laminar burning velocities are shown in black and blue in Figure 5A-D. Figure 5A shows the experimental data of laminar burning velocities based on 20% ammonia-80% methane-air flames with 0%, 20%, and 40% hydrogen blends compared with three different combustion models. One can see that the portion of ammonia will not affect the model's behavior. The Li [33] and Okafor [20] models underestimate any stoichiometric condition. In contrast, the Shrestha model [31] performs well for lean and stoichiometric conditions but tends to overestimate on the rich side due to an incomplete N\({}_{2}\)H\({}_{i}\) sub-mechanism and the doubling of the rate constant (NH\({}_{2}\) + NH = N\({}_{2}\)H\({}_{2}\) + H). The Li model [33] performed the best regarding the 60% ammonia-40% methane and 80% ammonia-20% methane-air flames with 20% and 40% hydrogen blends, as shown in Figure 5D,E. It seems that the Li model [33] is able to qualitatively predict the experimental trends of the lean and stoichiometric conditions when ammonia is the dominating fuel in the mixture. Figure 9 shows the adiabatic flame temperature and density ratio for NH\({}_{3}\)/CH\({}_{4}\)/air flames as a function of \(\phi\) for both binary and ternary fuel blends. It can be observed that hydrogen yields the highest adiabatic flame temperature, while ammonia results in the lowest temperature. The effect of the tertiary fuel can be clearly seen in Figure 9B,D, distinguishing it from the dual fuel blends, which closely resemble the data for pure methane. The density ratio remains relatively constant on the lean mixture side for single, binary, and ternary fuels.