Changes

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. <ref>Clark N. et al., Modelling and development of a linear engine, ''Proc. ASME Spring Conference, Internal Combustion Engine Division, 1998:30:49–57''.</ref><ref>Tikkanen S. et al., First cycles of the dual hydraulic free piston engine, ''SAE Paper 2000–01–2546, 2000''.</ref>.

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. <ref>Clark N. et al., Modelling and development of a linear engine, ''Proc. ASME Spring Conference, Internal Combustion Engine Division, 1998:30:49–57''.</ref><ref>Tikkanen S. et al., First cycles of the dual hydraulic free piston engine, ''SAE Paper 2000–01–2546, 2000''.</ref>.

Several free-piston gas generators were created, and these were in widely used in large-scale applications such as stationary and marine powerplants.  <ref>London A.L., Oppenheim A.K., The free-piston engine development -- Present status and design aspects, ''Transactions of the ASME 1952:74:1349–1361''.</ref>.  Current research suggests these could be more efficient than internal combustion engines <ref>[http://nextbigfuture.com/2008/09/free-piston-engine-could-be-twice-as.html]</ref>.

Several free-piston gas generators were created, and these were in widely used in large-scale applications such as stationary and marine powerplants.  <ref>London A.L., Oppenheim A.K., The free-piston engine development -- Present status and design aspects, ''Transactions of the ASME 1952:74:1349–1361''.</ref>.  Current research suggests these could be more efficient than internal combustion engines <ref>[http://nextbigfuture.com/2008/09/free-piston-engine-could-be-twice-as.html www.nextbigfuture.com]</ref>.

== References ==

== References ==

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