You have probably seen this before Neil.
It was originally conceived as an IC engine.
This video is running on 120 PSI shop air, but could easily be configured as an engine.
http://www.youtube.com/user/Ride122609
With variable stroke (not configured on the demo model) it could change compression and go to a no stroke position and use it's own spinning mass as short term storage.
Combined with a conventional CVT transmission it could P&G automatically without any additional driver input.
Notice the elimination of connecting rods, which are a major source of side loads on the pistons and most of the reason they need skirts to spread out the loads on the cylinder walls. Piston rods are the main reason why IV piston engines cylinders wear in a oval pattern on the sides 90 degrees in respect to the center line of the crankshaft.
regards
Mech