A comprehensive review of organic rankine cycle waste heat recovery systems in heavy-duty diesel engine applications

Effective recovery of heavy-duty vehicle waste heat is a key solution toward meeting the increasingly stringent fuel economy and CO2 emission standards. Different from previous publications, this paper presents a preliminary introduction of organic Rankine cycle waste heat recovery (ORC-WHR) in heavy-duty diesel (HDD) vehicle applications in the past decade. It presents a wide range of topics in the HDD vehicle ORC-WHR system development, including system architecture evaluation, heat exchanger selection, expander selection, working fluid selection, power optimization, control strategy evaluation, simulation and experimental work overview, and limiting factors. In the system architecture selection, the tradeoff between fuel savings and system complexity dominates. In the heat exchanger design, besides the heat exchanger efficiency, transient evaporator response is critical factor for the system control and performance. The expander type and configuration is closely coupled to the expander power output type (i.e. electricity or mechanical power). WHR power production is most sensitive to working fluid mass flow rate, with less sensitivities to expander speed and condenser coolant mass flow rate. The integration of ORC-WHR control with engine control shows potential to improve the waste heat recovery system performance. The simulation studies predict higher power recovery levels than that in experimental work (0-60 kW vs. 0-14 kW), which could result from the large number of heat resources, optimistic expander and pump efficiencies and neglected heat losses in the simulations.