A low-cost hybrid drivetrain concept based on compressed air energy storage

• Published in: Applied energy Vol. 134; pp. 477 - 489
• Main Authors: Brown, T.L., Atluri, V.P., Schmiedeler, J.P.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.12.2014; Elsevier
• Subjects: Applied sciences; CAES; Compressed air; Energy; Exact sciences and technology; Hybrid vehicles; Low cost; Pneumatic hybrid; Hybrid vehicles; CAES; Compressed air; Low cost; Pneumatic hybrid; Costs; Hybrid vehicle; Cost analysis; Energy storage
• ISSN: 0306-2619; 1872-9118
• DOI: 10.1016/j.apenergy.2014.07.111

•A new pneumatic hybrid concept is introduced.•A proof-of-concept prototype system is built and tested.•The experimental system has a round-trip efficiency of just under 10%.•A thermodynamics model is used to predict the performance of modified designs.•An efficiency of nearly 50% is possible with reasonable design changes. This paper introduces a new low-cost hybrid drivetrain concept based on compressed air energy storage. In contrast to most contemporary approaches to pneumatic hybridization, which require modification to the primary power plant, this concept is based on a stand-alone pneumatic system that could be readily integrated with existing vehicles. The pneumatic system consists of an air tank and a compressor–expander that is coupled to the rest of the drivetrain via an infinitely variable transmission. Rather than incorporating more expensive technologies such as variable valve timing or a variable compression ratio compressor, a fixed valve system consisting of a rotary valve and passive check valves is optimized to operate efficiently over a range of tank pressures. The feasibility of this approach is established by thermodynamic modeling and the construction of a proof-of-concept prototype, which is also used to fine tune model parameters. While the proof-of-concept system shows a round trip efficiency of just under 10%, modeling shows that a round trip efficiency of 26% is possible with a revised design. If waste heat from the engine is used to maintain an elevated tank temperature, efficiencies of nearly 50% may be possible, indicating that the concept could be effective for practical hybridization of passenger vehicles.