Exergy-based analysis for hybrid and electric ground vehicles

Federico Dettù, Gabriele Pozzato, Denise M. Rizzo, Simona Onori

The exergy, or availability, is a thermodynamic concept representing the useful work that can be extracted from a system which moves from a given state to an equilibrium point with the environment. It is also a system metric, formulated from the first and the second law of thermodynamics, encompassing the interactions between subsystems and their irreversibilities. Thus, an exergy-based analysis allows to identify the valuable portion of a system's energy, which can be converted into useful work. Within this framework, an exergy-based analysis for ground vehicles, namely, Electric Vehicles (EVs) and Hybrid Electric Vehicles (HEVs), is proposed. This study, a first to the authors' knowledge, builds a comprehensive modeling framework, accounting for the different energy storage/conversion devices of the powertrain, which can be employed to quantify how efficiencies and inefficiencies are distributed among the components of the propulsion system and drivetrain. This information is of paramount importance and can be employed for further optimization of the vehicle design or for the development of exergy management strategies aiming at minimizing inefficiencies, rather than fuel consumption. Eventually, the effectiveness and potentialities of the proposed approach are shown considering two case studies based on an EV and a parallel HEV, respectively.

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