Free piston engine
Free-piston air compressors were used, among others by, the German Navy. They were efficienct, compact and quiet.
These are of the dual piston type, creating a compact unit with a high/weight ratio. This design requires an electric machine of for low weight. Difficulties in the form of low cycle-to-cycle rates have been reported for dual piston engines.
Several free-piston gas generators were created, and these were in widely used in large-scale applications such as stationary and marine powerplants. Current research suggests these could be more efficient than internal combustion engines.
- Pescara R.P., Motor compressor apparatus, US Patent 1,657,641, 1928.
- Toutant W.T., The Worthington–Junkers free-piston air compressor, Journal of the American Society of Naval Engineers 1952:64:583–594.
- Clark N. et al., Modelling and development of a linear engine, Proc. ASME Spring Conference, Internal Combustion Engine Division, 1998:30:49–57.
- Tikkanen S. et al., First cycles of the dual hydraulic free piston engine, SAE Paper 2000–01–2546, 2000.
- London A.L., Oppenheim A.K., The free-piston engine development -- Present status and design aspects, Transactions of the ASME 1952:74:1349–1361.