Dean Kamen's Hybrid Scooter  

Gizmag has an article on Dean Maken's hybrid scooter design, which uses a Stirling engine - Dean Kamen developing eco hybrid that will run on anything that burns

Dean Kamen – the multimillionaire inventor behind the Segway personal transporter – is well down the road in the development of a new bike that combines electric power and a radical generator which will allow it to burn almost any fuel.

Built around a fairly conventional battery and electric motor combination to provide the drive to the wheel, something Kamen's experience with the much-hyped Segway makes relatively easy, the radical part of the design is the inclusion of a Stirling engine to recharge the bike's battery pack. Based on technology that pre-dates the internal combustion engine by nearly a century, the Stirling engine is closer in concept to a steam engine, using external combustion, and without the need for a fuel that can be injected and burned incredibly fast inside a normal engine's combustion chamber, it can run on virtually anything that burns – opening the door to easily renewable fuels rather than relying on dwindling fossil fuel supplies.

Although the prototype bike has yet to be shown in public, unlike Kamen's Stirling-engined car which has been demonstrated several times, Kamen himself is understood to have been using the prototype to zip around his own estate.

As revealed in Kamen's own patent for the technology, the bike looks like a conventional scooter, with the Stirling engine and its fuel tank mounted under the seat, a rechargeable battery pack in the floor and a radiator in the front fairing. Although the Stirling engine's low output – one this size is unlikely to make any more than 5bhp – means it can't give the bike much performance on its own, it's able to keep the battery topped up by continuing to supply electricity even when you're not moving. The energy reserves in the battery can be used when more power is needed. And as the Stirling engine could be left running at low speed even when the bike is parked, the battery would never be likely to go flat.

Kamen has already sunk more than $50 million into his development of Stirling engine technology, using the idea for everything from bikes to cars and even to water-purifiers to be used in the developing world.