Multi-objective optimization of organic Rankine cycle power systems for waste heat recovery on heavy-duty vehicles

The use of Organic Rankine Cycle (ORC) power systems for waste heat recovery on internal combustion engines of heavy-duty vehicles can help to mitigate the greenhouse gasses and reduce the fuel consumption of the truck. However, designing an ORC system for this application is a complex process involving trade-offs among factors such as the performance, space/weight restrictions, and cost. This paper presents a multi-objective optimization study of an organic Rankine cycle unit for waste heat recovery from heavy-duty vehicles from techno-economic and sizing perspectives. The optimization was carried out for seven different working fluids using the genetic algorithm to minimize the cost, volume and mass, and maximize the net power output of the ORC unit. The ORC performances for a driving cycle of a truck were also evaluated. In general, the results indicate that the mass, volume, cost and net power output of the ORC system increase with increase in evaporation temperature. The results suggest that when condensation temperature was decreased from 60 °C to 40 °C, the cost, volume, and weight of the ORC unit increased significantly. The maximum net power output, both at design and off-design conditions, is obtained with pentane as working fluid. For this design the net power output of the ORC unit is 10.94 kW at design condition and 8.3 kW at off-design (in average) condition, and the mass, volume, and cost of the ORC system are 129 kg, 1.077 m³, and 8527 €, respectively.