Single-loop organic Rankine cycles for engine waste heat recovery using both low- and high-temperature heat sources

• A novel single-loop organic Rankine cycle for engine waste heat recovery (WHR).
• Thermodynamic analyses of the novel system in comparison with conventional systems.
• Increasing the temperature of engine coolant to increase the net power of the system.
• Effects of pressure drop and efficiency of recuperator on performance of the system.
• Effects of changes in waste heat sources.

A highly efficient single-loop ORC (organic Rankine cycle) is proposed for engine WHR (waste heat recovery) from a gasoline vehicle. IC (Internal combustion) engines have two waste heat sources—exhaust gas and engine coolant—with similar quantities of energy but different temperatures. Dual-loop systems can obtain the maximum power output from engine WHR; however, the systems occupy large amounts of space and are complex, heavy, and economically unfavorable, particularly for vehicle applications. A highly efficient single-loop system can overcome such limitations. This paper compares the performances of conventional single-loop systems and proposes a novel single-loop ORC system for engine WHR from both low- and high-temperature sources. The novel single-loop system produces approximately 20% additional power from engine WHR when operating under the target engine conditions.