Dean Kamen is known widely as the inventor of the Segway personal transporter. However, over the past months he has been working on designing a new kind of Hybrid Scooter: A scooter that will make use of a Stirling Engine and be able to run on pretty much anything that will burn.
The Stirling Engine design has been around since the early 1800s. However, few have been able to find a well suited application for the relatively low amount of power they produce. The engine works by using a difference in heat to move a piston inside a sealed chamber. As gas is heated, it will expand and force the piston down. As the gas cools, it will contract and draw the piston back up. While several variants have been created, the one Mr. Kamen plans on using is a simple two-piston design.
The cycle begins with a small amount of heat being applied to the power cylinder. As the gas forces the piston down it turns the crankshaft and produces what would be a power stroke. Once at the bottom of its stroke, the power cylinder begins to rise again, relying on the momentum of the flywheel to maintain rotation. As it rises, it is forcing the gas through a transfer port into the displacer piston chamber. Once inside, the gas is cooled and begins to draw the displacer piston back to the top of its stroke. While this is happening, excess gas is being forced back into the power cylinder through the transfer port. Once the power cylinder has reached the top of its stroke, heat is applied and the cycle repeats.
The main reason for using a Stirling Engine is the simple fact that it is extremely efficient. Depending on the size of the pistons, a relatively small amount of heat can be applied to begin the cycle and often times can be reduced slightly to maintain a certain speed. This is also one of the inherent problems with using a Stirling Engine. They literally have to "warm up" before any usable amount of power can be produced.
Along with needing time to warm up, these engines have a low specific power. In other words, they need to be fairly large to produce a small amount of power. This is primarily due to the speed limitations of gas to transfer heat. When compared to an internal combustion engine that uses detonation to create a difference in heat, Stirling engines are much slower. This also leads to almost nonexistent throttle response if used in an automotive application.
Mr. Kamen was able to solve some of these issues with the simple addition of a battery and an electric motor. The scooter itself uses energy stored in a battery to power an electric motor that is mounted just in front of the rear wheel. The Stirling Engine will be used to turn a high output generator which will produce power for the electric motor. When just cruising around, the engine should be able to crank out enough electrons to keep you moving and keep the batteries fully charged.
A small burner will provide the necessary heat to being the process of turning the Stirling engine, while a front mounted radiator will keep cool air moving for the displacer piston. The burner is being designed to operate on anything that will ignite, which make running out of fuel much more difficult and since the 2 engines are independent of each other, the Stirling engine can be charging the batteries while parked.
The prototype scooter has not yet been demonstrated in public, but it is rumored that Mr. Kamen has been using it to get from place to place on his estate.Auto Blog Green via Gizmag