Performance Analysis of an Electric Turbocompounding System for a Hybrid Vehicle Diesel Engine

Abstract

Waste heat recovery (WHR) is one of the main approaches to improve the internal combustion engine (ICE) overall efficiency and reduce emissions. The electric turbocompounding (ETC) technology is considered as a promising WHR technology for vehicle engines due to its compactness and light weight. In order to improve the overall fuel efficiency of the engine at practical operating conditions, the impacts of the implementation of the ETC system should be investigated not only at engine full load conditions, but also under practical driving cycles. In this paper, an ETC system was designed for a 4.75 L diesel engine, in which a power turbine was installed down-stream to the turbocharger turbine. A performance simulation model of the ETC engine was developed on the basis of the diesel engine model, which was validated against engine performance experimental data. The control strategies of the wastegate of turbocharger turbine, the wastegate of power turbine and the operating torque of generator were determined. The relative variation in BSFC was studied under full range of operating conditions, and results show that the maximum improvement of fuel economy is 6.7% at an engine speed of 1000 rpm and 70% of full load, in comparison with the baseline diesel engine. Main factors lead to the performance differences between the ETC engine and the baseline engine were analyzed. Furthermore, the performance of the ETC engine under the C-WTVC driving cycle was investigated. Results show that the implementation of the ETC system resulted in a 1.2% fuel consumption reduction under the C-WTVC driving cycle.