The Scuderi Group has recently gained a lot of publicity with its “Air-Hybrid” engine that can double the fuel effciency of a car and decrease toxic emissions by as much as 80%.
The engine is a 'hybrid' in that it extracts energy that is normally lost, stores that energy, and then reuses it. The energy that is normally lost is airpressure, and it is stored for only an extremely brief moment before being forced into a combustion cylinder. The increased air pressure in the combustion cylinder effectively super-charges the engine cycle. The fuel burns hotter and more fully, and the Air-Hybrid engine is able to use more of that energy.
The engine is remarkably simple and very efficient. We're looking forward to seeing these things in mass-market cars.
For more information see this video on how the Scuderi Air-Hybrid Engine works.