The external-combustion engine predates its internal-combustion counterpart by nearly a century. Internal combustion won out for modern automobiles by way of its more robust production of horsepower and torque. But Segway inventor Dean Kamen is working up several new uses for the venerable Stirling external-combustion engine. The latest is a electric generator that can use almost anything that burns as fuel. It's the centerpiece of a new hybrid-electric scooter that may never need recharging.