Simultaneous optimization of cycle and expander design for truck on board waste heat recovery with ORC technology

Small-scale Organic Rankine Cycles (ORCs) represent a promising technology for waste heat recovery (WHR) from internal combustion engines (ICEs) for transport applications, due to their remarkable potential, especially on¬board of innovative long-haul trucks. Despite market leader companies have already proved its effectiveness, detailed system design procedures are scarcely available in the open literature and proposed solutions are often more simplified with respect to current industrial state¬of¬art. The present work describes a methodology to include within the ORC design and optimization procedure an efficiency map of the turbo¬expander, retrieved exploiting a mean line reduced¬order method developed in¬house. The developed ORC optimization algorithm allows to consider any working fluid in available thermodynamic databases and can investigate multiple cycle architectures. The approach proposed allows to design the thermodynamic cycle considering a realistic performance of the expander and to retrieve the best cycle architectures and turbine geometry depending on the heat source characteristic and active constraints. Methodology is applied to two WHR applications of different sizes highlighting the impact of adopting efficiency maps for the turbine within the cycle optimization procedure rather than assuming fixed efficiency values.