Thermodynamic Cycles for a New Hybrid Pneumatic–Combustion Engine Concept

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. This paper presents a new hybrid pneumatic – combustion engine concept, and the associated thermodynamic cycles, 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 can then be restored to start the engine, or charge the engine at full load. The regenerative breaking combined with the engine downsizing should provide a great improvement in terms of fuel economy in typical slowdown – acceleration situations.