Friction and lubrication

One of the main attractions of the free-piston engine concept is its simple design with very few moving parts. In addition to reducing manufacturing and maintenance costs and improving reliability, this significantly reduces frictional losses in the system. Compared with a conventional engine, frictional losses associated with the crank system are completely eliminated. Further, the side forces on the piston resulting from the connecting rod angle is removed, reducing piston skirt friction.

The very low frictional losses may allow alternative lubrication schemes to be employed for certain applications, such as the use of solid film lubrication. A secondary effect of lower engine frictional losses is a lower cooling system load, further improving the fuel efficiency of the free-piston engine. These topics are currently under more detailed investigation by the group in order to better understand friction mechanisms and lubrication requirements in the free-piston engine and to quantify advantages over conventional technology.