Parametric study on a novel steam injected inverted Brayton cycle system recovering waste heat from the internal combustion engine

Abstract

To fully explore the potential of recovering waste heat from the turbocharged internal combustion engine, this paper proposes a novel steam injected inverted Brayton cycle (IBC) system, with the IBC subsystem recovering excess exhaust pressure energy downstream of the turbocharger turbine and the steam injection subsystem utilizing waste heat from the IBC heat exchanger. First, the configuration and thermodynamic processes of this novel system are introduced, followed by detailed descriptions of model building and validation. Next, parametric simulations for the IBC system with steam injection are carried out, and optimization of the whole combined power cycle system is present at the end. The results show that the IBC turbine size has the biggest effect on the exhaust energy distributions across two turbines, followed by the bypass valve opening and the IBC power split ratio. To fully utilize the injected steam energy, the injected location should be upstream of the turbocharger turbine rather than upstream of the IBC turbine. The total fuel economy can be improved by 7.4 % at the rated condition. Considering the case swept optimization at different engine speeds, the fuel economy at the rated speed and the maximum torque speed can be improved by 3.5 % and 2.8 %, respectively.