THERMO-ECONOMIC OPTIMIZATION OF ORGANIC RANKINE CYCLE SYSTEMS FOR WASTE HEAT RECOVERY FROM EXHAUST AND RECIRCULATED GASES OF HEAVY DUTY TRUCKS

Waste heat recovery (WHR) ORC is a very promising technology for reducing fuel consumption and consequently the CO2 emissions of future heavy-duty trucks (HDT). Nonetheless, the adoption of this technology in the automotive domain requires specific R&D activities going from the system definition to the on-board integration.
This study focuses on the preliminary design phase of ORC systems recovering the heat wasted from two of the sources available on a HDT: the exhaust and recirculated gases. From these heat sources and their combinations, 6 possible architectures are identified. On the other hand, 4 volumetric expansion machine technologies are considered (Scroll, Screw, Piston and Vane Expanders). At the end, 24 topologies are modelled considering only the main components (Pump, Heat exchangers, Expansion machines).
A three-step optimization method is proposed to identify the most promising system. First, the most suitable design conditions are identified using a simple model of expansion machine. In a second step, the design phase, using more detailed models for the expansion machines, a thermodynamic and economic optimizations are performed. Finally, in a third step, the output power of the latter system models is maximized in off-design conditions.