Parametric optimization of a new hybrid pneumatic-combustion engine concept

Abstract

Although internal combustion engines display high overall maximum global efficiencies, this potential cannot be fully exploited in automotive applications: in real conditions, the average engine load (and thus efficiency) is quite low and the kinetic energy during a braking phase is lost. One solution to this problem is to switch to a new hybrid pneumatic-combustion engine concept, which is able to store energy in the form of compressed air. This energy can be issued from a braking phase or from a combustion phase at low power. The potential energy from the air tank can then be restored to start the engine, use the stored air to drive the engine as a pneumatic motor at low load or charge the engine at full load. Optimization of the compressed air tank maximum pressure and volume as well as the operating mode switching strategy provides an improvement in terms of fuel economy as high as 31 per cent if combined with engine downsizing.