Fuel is combusted in the free-piston linear generator, which speeds up the floating piston. The piston unit features permanent magnets. The linear relative movement between the permanent magnets and the coils enables the energy supplied by combustion to be extracted as electric power. The piston is braked by compression of a medium in a gas spring chamber and pushed back towards the combustion cylinder. Due to its design, the piston unit swings freely and is restricted by the combustion cylinder on one side and by the gas spring on the other.
The free-piston linear generator offers the following advantages compared to conventional combustion engines:
• Adjustment of the stroke, compression ratio and piston path to the operating point
• Improved partial load efficiency
• Compact design
• Balanced forces of inertia (low noise emission)
• Low production costs
• Flex-fuel compatible
The DLR is developing both the free-piston linear generator hardware and the control and regulation systems required for operation. As a preliminary highlight of a systematic development process, a function demonstration model was put into operation in 2013. With a variable stroke and compression, the system uses internal combustion in an Otto cycle process, an electromagnetic valve operating mechanism and direct petrol injection. This is the first time that a system of this type is available to be surveyed.