Research on a pneumatic hybrid engine with regenerative braking and compressed-air-assisted cranking

Abstract

With the aim of improving the energy efficiency of conventional vehicles, this paper proposes a pneumatic hybrid engine concept, which features regenerative braking and compressed-air-assisted cranking functions. In the regenerative braking mode, the engine works as a two-stroke compressor and converts the kinematic energy of the vehicle into compressed air. In the two-stroke air motor mode, a throttle valve in the intake manifold is used to block the ambient air, and an electropneumatic solenoid valve is employed to control the compressed-air injection. The compressor mode is modelled on the basis of thermodynamics and gas dynamics theories and is improved according to the bench test results of a single-cylinder engine converted from a two-cylinder diesel engine. Transient engine cranking tests are also conducted and are discussed. Urban driving-cycle simulation results show that the fuel consumption of a light-duty vehicle with a pneumatic hybrid system can be reduced by 8%.