Energy and exergy analysis of a novel turbo-compounding system for supercharging and mild hybridization of a gasoline engine

Number of hybrid vehicles has increased around the world significantly. Automotive industry is utilizing the hybridization of the powertrain system to achieve better fuel economic and emissions reduction. One of the options recently considered in research for hybridization and downsizing of vehicles is to employ waste heat recovery systems.In this paper, the addition of a turbo-compound system with an air Brayton cycle to a naturally-aspirated engine was studied in AVL BOOST software. In addition, a supercharger was modeled to charge extra air into the engine and Air Brayton cycle (ABC). The engine was first validated against the experimental data prior to turbo compounding. The energy and exergy analysis were performed to understand the effects of the proposed design at engine rated speed. Results showed that between 16 to 18% increase in engine mechanical power can be achieved by adding turbo-compressor.Furthermore, the recommended ABC system can recover up to 1.1 kW extra electrical power from the engine exhaust energy. The energy and exergy efficiencies were both improved slightly by turbo-compounding and BSFC reduced by nearly 1% with the proposed system. Furthermore, installing the proposed system resulted in increasing of backpressure up to approximately 23.8 kPa