Technically, the combustion engine in any hybrid vehicle is a range extender, but the term commonly refers to gasoline-fueled generators that are used to charge an electric vehicle’s battery pack but aren’t used to directly power the wheels. This is the set up used in “series” or “inline’ hybrids like the Chevy Volt, which differs from parallel hybrids like the Toyota Prius, where the wheels can be driven by the electric motor or the internal combustion engine (ICE). Researchers at the German Aerospace Center (DLR) have developed a new type of range extender that can be powered by a range of different fuels.
The free-piston linear generator comprises an internal combustion chamber, a linear generator, and a gas spring. It works in a similar way to a conventional ICE with the ignition of a fuel-air mix in the combustion chamber pushing the pistons. However, rather than converting the linear movement of the piston into the rotational movement of the crankshaft like a conventional ICE or the Range Extender engine from Lotus, the device converts the piston’s kinetic energy directly into electricity.
The explosion of the fuel-air mix pushes the pistons on either side of the central combustion chamber towards the gas springs, which decelerate the pistons and push them back. The device operates at a frequency of 40 to 50 Hz and produces up to 35 kW of power.
“Engineers have been aware of the principle of this drive unit for some time,” says Ulrich Wagner, DLR Director of Energy and Transport. “Through the installation of a gas spring, DLR researchers have now succeeded, for the first time, in operating this system in a stable manner. The challenge here was to develop a particularly powerful mechanism with a highly dynamic control unit that regulates the complex interactions between the individual components."
The control system created by the DLR engineers is able to accurately control the piston movement to within one tenth of a millimeter, while recognizing fluctuations in the combustion process and compensating for them. It also allows flexible adjustment of the compression ratio, piston speed and cubic capacity, which enables different fuels to be used, including gasoline, diesel, natural gas, bio-fuels, ethanol and hydrogen.
The free-piston linear generator’s versatility also allows the device to adapt to operate at optimal efficiency based on the vehicle’s speed and driving characteristics to reduce emissions. And without the crankshaft and camshaft components found in conventional combustion engines, the device is also constructed with fewer components. Its low-profile design also allows one or more units to be easily installed in the underbody area of a vehicle to provide an additional range of around 600 km (373 miles) without increasing the weight of the car.
Researchers at the DLR Institute of Vehicle Concepts in Stuttgart have demonstrated the feasibility of the range extender on a specially developed test bed and has partnered with Universal Motor Corporation GmbH to develop the technology and build a prototype. DLR believes the device will act as a bridging technology to make electric vehicles a more attractive option for car buyers who are still concerned about the limited range of electric vehicles.
DLR’s video outlining the free-piston linear generator can be viewed here.
Source: DLR
Great it's compact. But if it uses twice as much petrol as a regular engine, that's not so good, especially in an alleged 'green' car.
- Upscaling: Upscaling to a greater power output is possible in two different ways. Firstly, the swept volume per cylinder can be increased. Secondly, it is possible to use several units. This is the equivalent to today’s multi-cylinder engines – but in contrast to those, some of the cylinders / units of the FPLG can be deactivated completely in case they are not needed currently. - Cooling: Water cooling for combustion section, linear generator and gas spring with different temperature levels for the 3 subsystems. - Gas exchanged: Indeed, it is necessary to turbo- or supercharge the engine making sure the scavenging process works satisfactorily. - Power output: Our current function demonstrator generates up to 12 kW from a single piston module operated at a frequency of 20 Hz. For a production version the frequency will be increased and a layout with two pistons will be used. We expect an electrical power output between 20 and 35 kW per module to be most beneficial."
I think it could help eletric vehicles by extending the range in a green sort of way; IMO.
I just think its cool. :)
So while the automotive environment might be the most challenging to to design to, please don't neglect consideration for other (more mundane) applications!
re; Adam Lund
It is not a law of nature that 2-stroke engines have to be dirty. Simply giving one direct injection will massively improve its efficiency and clean up its exhaust.
Even If the generator is heavier than a conventional generator the weight increase in the generator is significantly less than the weight decrease from not having a crankshaft, and rotator bearings. There is less friction in this design. Only a fool has an ICE powered generator with gears adding friction between the engine and generator.