This engine Circular started out as a research proposal, they operated it on compressed air with great results.
The site has some of the best animations and explonations of the diffirance between Normal Recopricating Engines and the Radial Circular engines , but unfortunatlly you have to dig each and every one by your self , it is great but not user friendly.
If you expand the next hraph you can see relations between the effective arm torque and gas pressure and the full arm of radial engins and gas pressure , which would clarifay the diffirance between Piston angins and Radial / Circular engines. click on images to go directlly to site.
this next graph shows how much energy is wasted by Piston engine and gained back by Radial engines.
There is also a nice Reseach Paper by the People bhinde it , click here to download .
Please visit there site .
Brows there NOT so userfriendlly site , nice animations nice text , nice eplanations.