## 5 Result and Discussion
### Exergy Destruction Rate  
The reduction in system exergy destruction is an effective means of improving the system net output power. The investigation of exergy destruction can identify the component with the most potential for reducing exergy destruction. The present work focuses on the exergy destruction rates of exhaust gas from HTL evaporator (\(I_{\rm Hout}\)), LTL condenser (\(I_{\rm LC}\)), HTL evaporator (\(I_{\rm He}\)), condenser/evaporator (\(I_{\rm ce}\)), LTL preheater (\(I_{\rm Lpre}\)), HTL turbine (\(I_{\rm HH}\)), LTL turbine (\(I_{\rm LL}\)), and working fluid pumps (\(I_{\rm p}\)) with \(T_{\rm g1}\) for different HTL working fluids. Figure 14 illustrates that, when cyclopentane is used for HTL, \(I_{\rm Hout}\) and \(I_{\rm Lpre}\) decrease with the increase of \(T_{\rm g1}\), because \(\eta_{\rm g}\) and \(\eta_{\rm jw}\) are improved by increasing \(T_{\rm g1}\). Because the superheat degree is 0 K and the optimal HTL evaporation temperature initially fails to reach the upper limit, then reaches  
Figure 12: Effects of \(T_{\rm g1}\) on the heat utilization ratio of the engine exhaust gas. Figure 13: Effects of \(T_{\rm g1}\) on the heat utilization ratio of the jacket cooling water. the upper limit, and superheat degree is finally not 0 K. \(I_{\rm{Lc}}\) initially declines and then increases with \(T_{\rm{g1}}\). \(I_{\rm{He}}\) decreases initially with the increase in \(T_{\rm{g1}}\) because the HTL evaporation temperature can increase with the increase in \(T_{\rm{g1}}\) to improve temperature match. Afterward, the superheated cycle is used given the upper limit of the HTL evaporation temperature, which is unsuitable for increasing \(T_{\rm{g1}}\), thereby increasing \(I_{\rm{He}}\). \(I_{\rm{He}}\) decreases initially and then increases with \(T_{\rm{g1}}\). Moreover, \(I_{\rm{ce}}\), \(I_{\rm{Ht}}\), and \(I_{\rm{P}}\) increase initially and then decrease eventually. The variation in \(I_{\rm{Lt}}\) is also affected by the HTL evaporation temperature and superheat degree. \(I_{\rm{Lt}}\) remains unchanged initially, later increases, and finally decreases slowly with the increase in \(T_{\rm{g1}}\). When \(T_{\rm{g1}}\) is 523.15-538.15 K, \(I_{\rm{out}}\) is maximal at higher than 17% because \(\eta_{\rm{g}}\) is low. Furthermore, \(I_{\rm{Lc}}\) is the second largest exergy destruction rate. When \(T_{\rm{g1}}\) is 543.15-623.15 K, the \(\eta_{\rm{g}}\) is improved by increasing \(T_{\rm{g1}}\), and \(I_{\rm{Lc}}\) is maximal at higher than 15.5%. When \(T_{\rm{g1}}\) is 543.15-608.15 K, \(I_{\rm{Hout}}\) is the second largest exergy destruction rate at less than 10%; when \(T_{\rm{g1}}\) is 613.15-623.15 K, \(I_{\rm{He}}\) increases and becomes the second largest given the upper limit of the HTL evaporation temperature. The condenser/evaporator is also a component, which has a large exergy destruction rate. When \(T_{\rm{g1}}\) is 578.15-593.15 K, \(I_{\rm{ce}}\) exceeds \(I_{\rm{He}}\) and becomes the third largest exergy destruction rate. When \(T_{\rm{g1}}\) is 523.15-553.15 K, \(I_{\rm{Lpre}}\) is the fourth largest exergy destruction rate at higher than 5%; when \(T_{\rm{g1}}\) is 573.15-623.15 K, the heat absorption ratio of the jacket cooling water accounting for the total heat absorption decreases, and \(I_{\rm{Lpre}}\) decreases and becomes the second smallest exergy destruction rate considering the increase in exhaust gas heat absorption. When \(T_{\rm{g1}}\) is 568.15 K, the variation in \(I_{\rm{Ht}}\) is larger than \(I_{\rm{Lt}}\) because the HTL cycle type changes from a saturated to a superheated cycle. \(I_{\rm{P}}\) is minimal at less than 1%. Figure 15 presents that, when cyclohexane is used for HTL, \(I_{\rm{Hout}}\) and \(I_{\rm{Lpre}}\) decrease with the increase in \(T_{\rm{g1}}\) because \(\eta_{\rm{g}}\) and \(\eta_{\rm{jw}}\) are improved by increasing \(T_{\rm{g1}}\). When \(T_{\rm{g1}}\) is 523.15-598.15 K, the optimal HTL evaporation temperature does not reach the upper limit and is suitable for \(T_{\rm{g1}}\).