基于双有机朗肯循环的CNG发动机余热回收系统参数优化及工质选择

Parameter Optimization and Working Fluid Selection of Waste Heat Recovery System for CNG Engine Based on Dual Organic Rankine Cycle

为了充分利用CNG发动机的余热能量,根据CNG发动机的余热能分布特性设计了双有机朗肯循环系统,用来回收CNG发动机的排气能量、进气中冷能量以及冷却系统具有的能量。该双有机朗肯循环系统包括高温循环和低温循环,高温循环采用R245fa作为工质,用于回收CNG发动机排气能量;低温循环分别采用R245fa,R1234ze和R1234yf作为工质,用于回收进气中冷能量、高温循环冷凝过程中释放的能量以及发动机冷却系统的能量。在CNG发动机标定工况下,对双有机朗肯循环系统的参数敏感度进行了分析。结果表明:较高的高温循环蒸发压力和低温循环蒸发温度,较低的高温循环冷凝温度和低温循环冷凝温度可以提升双ORC系统的净输出功率和热效率;高、低温循环均选择R245fa的方案可以使系统具有较优的热力学性能。

In order to utilize the waste heat of CNG engine efficiently ,a dual organic Rankine cycle （ORC） system was de‐signed to recover the waste heat of exhaust gas ,intake air and cooling system .The dual ORC system included a high tempera‐ture （HT ） cycle and a low temperature （LT ） cycle .R245fa was used as working fluid to recover the exhaust energy at HT cy‐cle .And R245fa ,R1234ze and R1234yf were selected as working fluids to recover the waste heat of intake air ,condensation process of HT cycle and cooling system at LT cycle .At rated condition of CNG engine ,the parameter sensitivity of the dual ORC system was further analyzed .The results show that the higher evaporation pressure of HT cycle and evaporation tempera‐ture of LT cycle and the lower condensation temperature of both cycles can improve the net power output and thermal efficiency of dual ORC system .The optimal thermodynamic performance can be achieved by choosing R245fa as working fluid for both cycles .