## 3 Results and Discussions
### RORC Thermal Performance: Effect of Pressure Ratio  
In this section, the influence of different fluids under different pressure ratios on the behavior of the RORC system have been analyzed. Figure 6 shows that, for all cases, pentane is the fluid which presents the best performance of the system. Otherwise, MD4M and D6 show very similar values that are considerably below the values obtained in the system using the other fluids. Generally, by increasing the pressure ratio, the system performance improves. These results also serve to determine those fluids  
Figure 4: RORC system heat transfer diagram.  
Figure 5: Exergy destroyed fraction in each RORC system component.  
that could have been chosen for the detailed study in this research and could have obtained similar results to those achieved with the working fluids chosen for the development of the paper.  
The impact of the pressure ratio variability on Pump 2 for pentane, hexane, and octane is comparatively analyzed, due to environmental criteria, thermal stability, safety operation conditions, and lower GWP [61], which made it possible to observe how fluids influence the performance of the RORC system. Taking into account that, for all cases, the fixed values of condensing temperature (Tc) of 65 \({}^{\circ}\)C and pinch point of the evaporator (AP) of 100 were maintained, as shown in Figure 7a, as the pressure ratio \(\left(r_{p}\right)\) increases, better net power results are obtained for the pentane, in this case, for the same pressure ratio value of 4, it reaches a net power value of 71.85 kW, followed by Hexane with 62.01 kW, and finally octane with 49.74 kW.  
Since the main objective is to increase the thermal efficiency of the cycle, it is seen in Figure 7b,c that pentane has the correct behavior for use such as the working fluid in the RORC cycle, since a pressure ratio of 5 has a thermal efficiency in the overall system of 14.55 and a RORC thermal efficiency of 14.96, whereas, for the same pressure ratio condition with hexane, the overall thermal efficiency is 14.47 with a RORC thermal efficiency of 14.46, and for octane a thermal efficiency in the overall system of 11.96 and a RORC thermal efficiency of about 11.95.  
Figure 7 shows by the increase of the pressure ratio, that pentane achieves the highest exergetic efficiency, i.e., approximately 32% for a pressure ratio of 6, as compared with hexane and octane. For hexane, an overall exergetic efficiency was achieved that ranged from 21% to 31%, for a pressure ratio variation from 3 to 6, respectively. Similarly, for the case of octane, an overall exergetic efficiency of about 17% to 26% was obtained for a variation of pressure ratio from 3 to 6, respectively, which shows a better performance in exergetic efficiency for hexane than for octane. Therefore, for all the fluids considered, an increase in the variables taken into account in the analysis is shown for a range of pressure ratio from 3 to 6, of which, in all cases, pentane obtained a better performance than the other fluids, which confirms the selection of pentane as a good candidate for the working fluid for this type of system.  
Figure 6: Performance of the RORC configurations with different working fluids and varying pressure ratios. (**a**) Net power; (**b**) Absolute increase in thermal efficiency; (**c**) Overall exergetic efficiency; and (**d**) Specific engine fuel consumption-ORC.