A comparative analysis of waste heat recovery systems in vehicles and their viability in real-world applications

Abstract

In motor vehicles, an average of 60-70% of the overall fuel energy is dissipated primarily through the heated exhaust gases and engine coolant, which accounts for 90% of an engine’s thermal output. The fuel efficiency and environment impact of vehicles can therefore be improved by implementation of systems designed to recover this wasted energy. This meta- study explores the current methods for waste heat recovery (WHR) currently in production and research phases. A comparison is also made between the thermodynamic viability of each proposed system, from which future strategies to maximise the efficiency of WHR systems can be obtained. These include the use of the organic Rankine cycle (ORC), thermoelectric generators (TEG), and regenerative braking. The purpose of this paper is to analyse the current state of research for waste heat recovery in vehicles and therefore provide a basis for further research and investigation. The results indicate a promising future for further study of ORCs in the field of WHR for internal combustion engines (ICE) in vehicles. This is due to the various design opportunities that ORCs offer, including multiple loop configurations, different working fluids and integration of thermal energy storage devices. Current research for TEGs indicate a high cost to efficiency ratio for the materials required for production, meaning that TEGs are not as viable of a solution for WHR in vehicles relative to ORCs. This paper concludes that a fuel savings of 8-19% can be achieved through the integration of multiple energy recovery systems. Keywords: Waste Heat Recovery; Vehicles; Thermodynamics; Organic Rankine Cycle; Thermoelectric Generators; Regenerative Braking; Exergy