## 3 Operating Characteristics of the ICE-ORC System  
### Performance Under the Rated Power Condition  
The performance of the ORC system when the engine operates under the rate power condition was investigated. The influences of the working parameters of the ORC system were evaluated and \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** & **Unit** \\ \hline Plate length & 300 & mm \\ Plate width & 200 & mm \\ Channel height & 3 & mm \\ Channel number & 45 & — \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The main parameters of the condenser. the optimal parameters were obtained. The results for the engine performance under the rated power are given in Table 4.  
Based on the established ICE-ORC model, the simulated performances of the ORC system as a function of the pump speed and the expander speed when the ICE operates under the rated power condition are shown in Figure 5. The results for the net power output are shown in Figure 5a, which increased significantly as the expander speed decreased. The influence of the pump speed was relatively small. When the expander speed was high, the net power reduced as the pump speed rose. When the expander speed was low, an opposite tendency was observed. From the measured performance characteristics of the single-screw expander in [PERSON] et al. [42], the efficiency of the expander increased as the mass flow rate rose under a low expander speed. However, the efficiency of the expander decreased with the mass flow rate when the expander speed was high. Therefore, the net power output showed a similar trend. The maximum net power reached 3.08 kW with an expander speed of 1350 r/min and a pump speed of 2350 r/min. The evaporation pressure will increase as the expander speed reduces, which is beneficial for the improvement of the net power output. However, if the expander speed is too small, the efficiency of the expander will decrease, resulting in a low net power output again. The efficiency of the expander reaches a high level with an expander speed in the range of 1300-1500 r/min [42]. Therefore, a maximum net power output is achieved with an expander speed slightly higher than 900 r/min. The results for the thermal efficiency of the ORC are shown in Figure 5b. The surface of the thermal efficiency exhibited a similar tendency with that of the net power output because the heat transfer quantities inside the evaporator were very close for different operation conditions defined by the pump speed and the expander speed. For the designed ORC system, the maximum thermal efficiency reached 4.5% accordingly. The influences of the working parameters on the system performance were analyzed further and the results are shown in Figure 6. The net power as a function of the evaporation pressure and the mass flow rate of R245 fa is displayed in Figure 6a. The net power increases apparently as the evaporation pressure increases because the enthalpy difference between the inlet and outlet of the expander is increased. The pump speed and the expander speed are two important working parameters that will influence the evaporation pressure. In this study, the pump speed was used to control the mass flow rate and the expander speed was used to control the evaporation pressure. When the pump speed keeps constant, the evaporation pressure will increase as the expander speed decreases. Therefore, a maximum net power was achieved under a low expander speed as shown in Figure 5a. Results for the outlet temperature of the evaporator are shown in Figure 6b. The corresponding outcomes for the superheat degree of the working fluid at the outlet of the evaporator are shown in Figure 6c. The outlet temperature decreased evidently as the mass flow rate increased. If the mass flow rate was small, the specific enthalpy difference between the inlet and outlet of the evaporator enlarged, leading to a high outlet temperature. The superheat degree would increase accordingly. Meanwhile, the waste heat of the exhaust gas could not be utilized fully.