A Combined Organic Rankine Cycle With Double Modes Used for Internal Combustion Engine Waste Heat Recovery

Abstract

A combined organic Rankine cycle (ORC) was proposed for both engine coolant energy recovery (CER) and exhaust energy recovery (EER), and it was applied to a gasoline direct injection (GDI) engine to verify its waste heat recovery (WHR) potential. After several kinds of organic working medium were compared, R123 was selected as the working fluid of this ORC. Two cycle modes, low-temperature cycle and high-temperature cycle, were designed according to the evaporation way of working fluid. The working fluid is evaporated by coolant heat in low-temperature cycle but by exhaust heat in high-temperature cycle. The influence factors of cycle performance and recovery potential of engine waste heat energy were investigated by cycle simulation and parametric analysis. The results show that recovery efficiency of waste heat energy is influenced by both engine operating conditions and cycle parameters. At 2000 r/min, the maximum recovery efficiency of waste heat energy is 7.3% under 0.2 MPa brake mean effective pressure (BMEP) but 10.7% under 1.4 MPa BMEP. With the combined ORC employed, the fuel efficiency improvement of engine comes up to 4.7% points under the operations of 2000 r/min and 0.2 MPa BMEP, while it further increases to 5.8% points under the operations of 2000 r/min and 1.4 MPa BMEP. All these indicate that the combined ORC is suitable for internal combustion (IC) engine WHR.