## 3 Results  
### Power Generation with or without Waste Heat Integration  
In Figure 4, the round trip efficiency (RTE) is plotted against the compressor pressure ratio (\(\Pi\)) for power generation with or without heat integration. Each marker represents a concept, with lighter markers indicating a lower compressor discharge temperature (CDT) of 450 \({}^{\circ}\)C and darker markers indicating a CDT of 625 \({}^{\circ}\)C. The markers outlined in red represent concepts using CO\({}_{2}\) as the working fluid, while those outlined in green represent concepts using Argon. Square markers represent concepts with a recuperator, while diamonds indicate concepts with a recuperator only in the charge line, and squares indicate concepts with a recuperator in both the charge and discharge lines for transferring heat from the hot to the cold side.  
The range of calculated RTE values is between 20 and 50%. The diagram also includes concepts that exhibit very high pressure. These result from low compressor inlet temperatures, where cooling to ambient temperatures is applied, for example, and the simultaneously relatively high specified compressor discharge temperature of 625 \({}^{\circ}\)C. This can be easily explained thermodynamically using the isentropic equation, especially for the working fluid CO\({}_{2}\). However, in addition to the high pressure ratio, these solutions exhibit low RTE values. In the search for promising concepts, it is therefore useful to limit the presentation of results to a pressure ratio range of 0 to 10, as shown in Figure 5.  
Figure 4: Pure electricity generation without waste heat integration: RTE over \(\Pi\) (complete solution area).  
It is evident that concepts operating at CDT = 450 \({}^{\circ}\)C exhibit lower RTE values compared to those with 625 \({}^{\circ}\)C as the maximum temperature in the cycle. This can be thermodynamically explained by the definition of Carnot efficiency. The Carnot efficiency indicates that the theoretical maximum efficiency of a heat engine increases with the temperature difference between the heat source (in this case, the compressor discharge temperature) and the heat sink. Consequently, systems operating at a higher CDT of 625 \({}^{\circ}\)C have a greater potential for higher efficiency, leading to improved RTE values. Regarding the use of different working fluids, no trend is apparent. The same applies to the inclusion or exclusion of recureptors.  
For future more detailed investigations, the leading concepts for pure electricity generation without waste heat integration are defined as those with the highest RTE for CDT = 450 \({}^{\circ}\)C and CDT = 625 \({}^{\circ}\)C, as shown in Figure 5:  
* PEG1: Working fluid Air. Cooler before the compressor in the discharge line. \(\delta_{\text{max}}\) = 625 \({}^{\circ}\)C; RTE = 49.5%; \(\Pi\) = 2.6. Flow diagram: Figure 6.
* PEG2: Working fluid Air. Cooler before the turbine in the charge line. \(\delta_{\text{max}}\) = 450 \({}^{\circ}\)C; RTE = 42.9%; \(\Pi\) = 2.7. Flow diagram: Figure 7.  
Figure 5: Pure electricity generation without waste heat integration: RTE over \(\Pi\) (restricted solution area).  
Figure 6: Lead concept PEG1 for pure electricity generation without waste heat integration.  
The additional integration of waste heat leads to more physically feasible solutions than without heat input. However, it is also noticeable that this does not result in significant improvements in terms of the level of RTE. Therefore, it is not meaningful to discuss these results in detail. Accordingly, for future detailed investigations, no concepts with waste heat integration are selected for pure electricity generation.