Free piston engine

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The free-piston engine was proposed by R.P. Pescara [1] and the original application was a single piston air compressor.

Free-piston air compressors were used, among others by, the German Navy. They were efficienct, compact and quiet.[2]

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.[3][4]

Several free-piston gas generators were created, and these were in widely used in large-scale applications such as stationary and marine powerplants.[5] Current research suggests these could be more efficient than internal combustion engines.[6]


  1. Pescara R.P., Motor compressor apparatus, US Patent 1,657,641, 1928.
  2. Toutant W.T., The Worthington–Junkers free-piston air compressor, Journal of the American Society of Naval Engineers 1952:64:583–594.
  3. Clark N. et al., Modelling and development of a linear engine, Proc. ASME Spring Conference, Internal Combustion Engine Division, 1998:30:49–57.
  4. Tikkanen S. et al., First cycles of the dual hydraulic free piston engine, SAE Paper 2000–01–2546, 2000.
  5. London A.L., Oppenheim A.K., The free-piston engine development -- Present status and design aspects, Transactions of the ASME 1952:74:1349–1361.