## 5 Result and Discussion
### Operating Parameter  
When the HTL working fluid is given, the variation in optimized HTL evaporation temperature, HTL condensation temperature, HTL superheat degree, exhaust gas temperature at the exit of the HTL evaporator and heat utilization ratio, exergy destruction rate with an increase in \(T_{\rm g1}\) for the four LTL working fluids are similar, and the systems with maximal net power output for four HTL working fluids are investigated. The four systems identified are cyclopentane + R1234 ze(E), cyclohexane + R1234 ze(E), benzene + R1234 ze(E), and toluene + R245 fa. Figure 8 depicts the effects of \(T_{\rm g1}\) on the optimal HTL evaporation temperature. With the increase in \(T_{\rm g1}\), the increasing HTL evaporation temperature can improve temperature match with exhaust gas. The optimal HTL evaporation temperature increases initially for the cyclopentane system. When \(T_{\rm g1}\) rises to 558.15 K, the optimal HTL evaporation temperature reaches the upper limit. When cyclohexane is used for HTL, the optimal HTL evaporation temperature increases initially with \(T_{\rm g1}\). When \(T_{\rm g1}\) rises to 603.15 K, the optimal HTL evaporation temperature reaches the upper limit. When benzene is used for HTL, the optimal HTL evaporation temperature initially increases with \(T_{\rm g1}\). When \(T_{\rm g1}\) rises to 618.15 K, the optimal HTL evaporation temperature reaches the upper limit. Given the high upper limit of the HTL evaporation temperature, for the toluene system, the optimal HTL evaporation temperature increases with \(T_{\rm g1}\). Figure 9 demonstrates the effects of the \(T_{\rm g1}\) on the optimal HTL condensation temperature. The optimal HTL condensation temperature remains unchanged for cyclohexane, benzene, and toluene systems, and the optimal HTL condensation temperature is the lower limit (the saturated temperature at the pressure of 101 kPa); moreover, the low HTL condensation temperature will enhance the DORC performance, and similar results are obtained by several parameter analysis studies [5; 21; 23; 43]. The optimal HTL condensation temperature increases with 523.15-563.15 K \(T_{\rm g1}\) when cyclopentane is used for HTL, and the saturated cycle is used. The superheated cycle is used when \(T_{\rm g1}\) is raised to 568.15 K, and the optimal HTL condensation temperature remains unchanged. It is higher than the lower limit (322.3 K) because the decrease in HTL condensation temperature will decrease \(T_{\rm g3}\), and \(T_{\rm g3}\) must be higher than or equal to the exhaust gas acid dew point temperature to  
Figure 8: Effects of \(T_{\rm g1}\) on the optimal HTL evaporation temperature. avoid low-temperature acid corrosion. Moreover, when the HTL condensation temperature increases to 351.0 K, \(T_{\text{g3}}\) is equal to the exhaust gas acid dew point temperature and maintains at 351.0 K.  
The HTL evaporation temperature upper limits are high, given the high critical temperatures of cyclohexane, benzene, and toluene. When \(T_{\text{g1}}\) increases, the increasing HTL evaporation temperature can improve the temperature match with the heat source, the superheated cycle is unnecessary, and the optimal HTL superheat degree is 0 K for cyclohexane, benzene, and toluene systems. In particular, the saturated cycle will generate more power output than the superheated cycle for these systems. However, the HTL evaporation temperature upper limit for the cyclopentane system is lower than other working fluids. When \(T_{\text{g1}}\) increases to 568.15 K, the HTL evaporation temperature is unsuitable for increasing \(T_{\text{g1}}\), and the superheated cycle is used to improve temperature match between the engine exhaust gas and HTL given the limit of the HTL evaporation temperature.