Waste Heat Recovery From Internal Combustion Engines: Feasibility Study on an Organic Rankine Cycle With Application to the Ohio State EcoCAR PHEV

This paper presents a feasibility analysis on the application of Organic Rankine Cycles as a Waste Heat Recovery system for automotive internal combustion engines. The analysis is conducted considering the Ohio State University EcoCAR, a student prototype plug-in hybrid electric vehicle, as a case study for preliminary fuel economy evaluation. Starting from a energy-based powertrain simulation model validated on experimental data from the prototype vehicle, a first and second-law analysis was conducted to identify the potential for engine waste heat recovery, considering a variety of driving cycles and assuming the vehicle operating in charge-sustaining (HEV) mode. Then, a quasi-static thermodynamic model of an Organic Rankine Cycle (ORC) was designed, calibrated from data available in literature and optimized to fit the prototype vehicle. Simulations were then carried out to evaluate the amount of energy recovered by the ORC system, considering both urban and highway driving conditions. The results of the simulations show that a simple ORC system is able to recover up to 10% of the engine waste heat on highway driving conditions, corresponding to a potential 7% improvement in fuel consumption, with low penalization of the added weight to the vehicle electric range.