## 2 Method
### Design of the O2 Production System
#### 2.3.3 Layout Optimization  
Turbocharging System  
Different turbocharging setups were analyzed to find the configuration that best meets the established optimization parameter. The study conducted for each arrangement was carried out as follows. Maintaining the size of the turbocharger receiving air from the atmosphere, i.e., TCH-1 NA in Figures 4-6, a sweep of the size scale factor of the second turbocharger is performed, i.e., TCH-2 ON in Figures 4 and 5, and TCH-2 NA in Figure 6. Simultaneously with the previous point, the corrected mass flow factor of the compressor, corresponding to each scale factor, is adjusted to operate in the most efficient island of the map. Finally, the fuel consumption of the burners obtained along the sweep is used as the objective function to find the best size ratio between the turbochargers.  
At the end of this stage, the best turbocharging configuration for the final O\({}_{2}\) production model is selected. Each of the layouts studied is explained below.  
* _Parallel configuration:_ The first turbocharging proposal consists of connecting two units in parallel with a common N\({}_{2}\) line at the inlet of the turbines. The TCH-1 NA turbocharger is placed at the beginning of the air flow line and the TCH-2 ON turbo at the end of the O\({}_{2}\) line to achieve the required O\({}_{2}\) partial pressure gradient in the MIEC. This parallel configuration is shown in the light blue box in Figure 4.
* _Serial configuration:_ Maintaining the location of the turbochargers in the scheme, the second turbocharging attempt was a series turbine configuration in which the N\({}_{2}\) line is regulated by a bypass valve to first drive the TCH-2 ON turbine and then, when the N\({}_{2}\) flow confluences again, drive the TCH-2 ON turbine. The bypass valve lift was swept to determine the best possible value. This serial configuration is shown in the light blue box in Figure 5.
* _Two-stage air compression:_ The third configuration analyzed was another serial arrangement, but in this case for both turbines and compressors. The air is compressed twice to further increase the partial pressure gradient in the MIEC without the need to generate vacuum. This configuration is shown in the light blue box in Figure 6; the heat exchanger system is different from that shown in the previous figures because, as will be demonstrated in the results section, the EGR line burner is not necessary for this setup at full engine load.  
Figure 4: O\({}_{2}\) production system with parallel turbocharging system.  
The latter option, which is the best of the three turbocharging systems (justification in Section 3), was adapted to work at all other engine operating points. The study shows that, in order to reach the required air conditions in the MIEC, the incorporation of the EGR burner line is only necessary at the two lowest engine load points. This addition is represented in Figure 6.  
MIEC Membrane  
As indicated in the description of the layout conception, the membrane area initially selected for the design of the O\({}_{2}\) production system was 6000 m\({}^{2}\). It is worth mentioning that a sweep of the membrane area was performed and will be presented in the results section with the aim of obtaining the optimal membrane area for the O\({}_{2}\) production system.  
Figure 5: O\({}_{2}\) production system with serial turbocharging system.  
Figure 6: O\({}_{2}\) production system with two-stage air compression system for all engine operating points.