## 3 Calculation Results and Discussion
### Hybrid System Off-Design Performance Evaluation under Variable Operation Parameters
#### 3.3.1 Effect of O/C Ratio Variation on the Hybrid System Performance  
Research findings highlight CPOx as the optimal choice for aviation fuel reforming in both aviation and aerospace applications, justifying its inclusion in this study [49]. The performance of the CPOx reactor exhibits variations based on factors such as pressure, temperature, and fuel/air inlet conditions. In this assessment, the O/C ratio of the CPOx reformer is identified as a pivotal parameter due to its significance in achieving optimal  
Figure 4: CPOx H\({}_{2}\) outlet flow variation with change in O/C ratio [48]. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Simulation Data** & **Referenced Data**[48] & **Relative Error** \\ \hline Inlet air temperature & 850.22 K & 873.15 K & 3\% \\ Fuel inlet temperature & 643.15 K & 643.15 K & 0 \\ Reactor temperature & 1045 K & 1037.15 K & \(-\)0.76\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: CPOx performance data validation. performance at design point. Given its close association with the CPOx reformer, the initial evaluation focuses on its influence on the reformer itself. The subsequent analysis extends to the immediate component affected by CPOx performance, the SOFC, with a comprehensive examination of its impact. The overall effects on the hybrid system are meticulously examined, leading to conclusive insights. Throughout this analysis, key parameters are maintained at specific values: the reactor pressure is consistently set at 300 kPa, the HPC outlet air split ratio is held at [0.00475(reformer):0.84532(cathode):0.15(combustor)], the current density is fixed at 5000 Am\({}^{-2}\), the HPC outlet air temperature is maintained at a constant 850.22 K, the heat exchanger effectiveness (HX-\(\xi\)) remains steady at 23%, the completely vaporized fuel is injected at a constant temperature of 643.1 K [48], the GT FAR is sustained at 0.02715, and the total engine inlet air flow is kept constant. With the other parameters held constant as aforementioned, the O/C ratio becomes the main variable parameter in the CPOx reactor, significantly influencing the fuel generation capabilities of the reactor. Figures 5 and 6 illustrate the effect of variation in the O/C ratio. A variable O/C ratio implies a change in the CPOx inlet fuel flow rate to accommodate this change in O/C ratios, as shown in Figure 6, as the CPOx inlet air flow rate is held constant. Along the flight profile, the SOFC power output is changing, and this subsequently influences the performance of the CPOx, effecting its outlet flow fractions to cater to variable SOFC fuel utilization. Figure 5 displays the composition of species in the outlet flow of the reactor. Examining the figure reveals that the composition of species in syngas is notably influenced by the selected O/C value. Specifically, the O/C variation shows that the molar fractions of hydrogen (H\({}_{2}\)) peak at lower O/C ratios (the partial oxidation regime), and beyond an O/C ratio of 0.9, the H\({}_{2}\) molar fractions begin to decrease. Additionally, our analysis includes a critical assessment of carbon (C) formation, which is predominant at lower O/C ratios. Consequently, this consideration plays a pivotal role in the selection of the optimal O/C ratio, as achieving a lower carbon molar fraction is desirable for enhancing the CPOx performance. Furthermore, the exothermic nature of the catalytic partial oxidation reaction presents a secondary constraint, as lower reactor temperatures are preferable to mitigate heat sintering. The ideal generation of syngas is observed at an O/C ratio of approximately one-third of stoichiometric air for combustion  
Figure 5: CPOx reactor outlet flow molar fraction variation with O/C ratio. (O/C = 0.33). However, this region is characterized by a high presence of soot and intense cooking-graphite formation, rendering it unsuitable for system application. It is therefore important to note that lower O/C ratios, while yielding higher syngas production, are constrained by the increased formation of graphite.