Integrated design of working fluid and organic Rankine cycle utilizing transient exhaust gases of heavy-duty vehicles

Abstract

Heavy-duty vehicles waste a major part of their fuel energy in the exhaust gas. To recover energy from the exhaust gas, Organic Rankine Cycles are a promising technology. However, both, the Organic Rankine Cycle and its working fluid have to be tailored to the transient energy input by the exhaust gas. For this purpose, we developed the so-called 1-stage Continuous-Molecular Targeting - Computer-aided Molecular Design (1-stage CoMT-CAMD) method. 1-stage CoMT-CAMD integrates the design of novel working fluids as degree of freedom into the process optimization. However, so far, 1-stage CoMT-CAMD is limited to a nominal operating point. In this work, we enable the integrated design for transient heat sources by combining 1-stage CoMT-CAMD with aggregation techniques. Aggregation techniques allow us to represent the many operating points due to the transient heat source by a few aggregated operating points serving as input for the integrated design. A subsequent assessment of the identified working fluids ensures safety and environmental friendliness. The resulting algorithm is applied to the design of an Organic Rankine Cycle on heavy-duty vehicles using the VECTO long haul cycle to characterize the transient exhaust gas. For this case study, 6 aggregated operating points are sufficient to represent the transient exhaust gas accurately. The optimal identified working fluid is ethyl formate and increases the net power output by 30% compared to the commonly used working fluid ethanol.