## 4 Sensitivity Analysis to Air Management Parameters  
The system response to the parameter changes introduced in Table 1 is now explored. Figure 7 shows the results in terms of the balance of plant efficiency versus current density results for the different studies performed. These include the excess oxygen ratio, the turbine and compressor efficiencies, and the pressure ratio across the membrane. In each study, only  
Figure 5: Compressor power consumption and recovered power per unit of active area of the stack as a function of current density and O\({}_{2}\) molar fraction. Figure 6: Balance of plant (BOP) efficiency as a function of current density and O\({}_{2}\) molar fraction. one parameter was varied from the case previously discussed. Additionally, the full sensitivity of O2 enrichment (for an oxygen molar fraction of 0.22 to 0.4) was computed, but only the value that maximizes the average efficiency over the entire polarization curve was selected for the comparison. The legend for each curve also includes the selected O2 enrichment level. The first parameter studied was the excess O2 ratio of the cathode through the value of \(\lambda_{\text{O}_{2}}\), shown in the upper left corner of the figure. As can be seen, there is a non-negligible improvement, around 2% absolute, if a reduction in this excess O2 ratio up to a value of 1.2 is considered. This is due to the lower compressor power associated with the lower air mass flow. It should be noted that, as previously discussed, it is expected that the need to operate with high excess ratios would be reduced as the proportion of O2 in the cathode stream increases, which is in favor for the possible implementation of the proposed technology. However, above a certain value of \(\lambda_{\text{O}_{2}}\), the sensitivity to the excess O2 ratio is significantly reduced, since a large part of the extra consumption produced by the compressor can be recovered in the expansion of the turbine present at the outlet of the membrane retenate gas. The second parameter covered is related to the level of compression that is necessary to enable the operation of the polymeric O2-N2 separation membrane (\(\pi_{memb}\)). The results of this study are presented in the graph in the lower left corner of the figure. As can be seen, this is the parameter that presents the greatest potential for improvement of the performance of the system by almost linearly reducing the power consumed, achieving improvements of more than 4% in absolute performance. In this regard, it must be noted that the present study was based on a performance map from a commercial membrane, model NM C05, from UBE Corporation. However, other membrane technologies with better selectivity levels (i.e., with a higher capacity to separate O2 from N2) are being evaluated according to the literature [42]. If membranes with such capability become commercially available, it would be possible to achieve similar enrichment levels at lower pressure ratios, further enhancing the system potential. Figure 7: Analysis of the effect of the cathode’s excess O2 ratio, compressor efficiency, turbine efficiency, and membrane pressure ratio on system efficiency. Finally, sensitivity studies were conducted with respect to the isentropic efficiencies of both the compression (upper right corner) and expansion (lower right corner) stages of the existing turbomachinery. From the compression study, it was found that it is necessary to ensure compressor efficiencies above 60% for the proposed technology to present advantages in terms of system performance. The effect on turbine efficiency is less significant in comparison, although a threshold limit of 70% can also be set to ensure an operating area where the new architecture presents reasonable advantages for its implementation.