A study of nine different pure organic working fluids for organic Rankine cycle (ORC) engine waste heat recovery by a team from Beijing University of Technology, Tsinghua University, and the Chinese Academy of Sciences found that R11, R141b, R113 and R123 manifest slightly higher thermodynamic performances than the others; however, R245fa and R245ca are the most environment-friendly working fluids for engine waste heat-recovery applications.
A paper on their work appears in the journal Energy.
Organic Rankine Cycle (ORC) can be used to recover low-grade waste heat. When a vehicle is running, the engine exhaust gas states have a wide range of variance. Defining the operational conditions of the ORC that achieve the maximum utilization of waste heat is important.
The results from the nine fluids were compared in the regions when net power outputs were fixed at 10 kW. Safety levels and environmental impacts were also evaluated. Among their findings were that the condensing temperature has more important effect than the evaporating pressure to the performance of ORC.
E.H. Wang, H.G. Zhang, B.Y. Fan, M.G. Ouyang, Y. Zhao and Q.H. Mu (2011) Study of working fluid selection of organic Rankine cycle (ORC) for engine waste heat recovery. Energy doi: 10.1016/j.energy.2011.03.041