Here's a 4 stroke engine concept you have to see to understand, the Peraves Superballmotor uses a multipart sphere to replace the usual crankshaft, rods and pistons of a normal internal combustion engine.
The moving parts of the sphere have ceramic balls on their exterior which travel in grooves in the case surrounding the sphere. The rotating motion of the sphere causes the moving parts, which serve as pistons, to go through the 4 stroke cycle in 2 working chambers, which would be comparable to a 2 cylinder engine. Air and fuel are introduced at the sides near the rotating axis, are supercharged through the use of prechambers, flow into the gaps in the sphere created by the motion of the sphere, followed by compression, power and exhaust as you would expect. You have to watch the animation on their site to see the whole process because a description doesn't work very well.
Peraves builds the Monotracer and the Ecomobile, fully enclosed 2 wheel motorcycles, which have been out there for some time, but I never saw this engine before, I don't know if it's new, but it's new to me. They have it set up in a Yamaha YP-400 scooter and they say it can be built as a gasoline, diesel, CNG or hydrogen engine. As with any internal combustion engine, it can be used in various applications besides motor vehicles.
If you're a reasonably experienced motorhead, you can understand how working on one machine can lead you to play with the parts in various ways and come up with variations that do something else entirely. But, after looking at the animation and understanding how it works, it's seems like quite a stretch from any other engine or machine to this design, I'd be curious to know how that mental leap occured. What similar device would lead someone, by extension, to put pieces together this way.
It's a very cool idea. Is it workable or better than other engines? Hard to say. Their website says it has many advantages in power to weight, lower cost and more power at lower rpm but their charts are small and hard to read so we'll have to take their word for it. I'd like to hear it run and see some power numbers to form any conclusions, but, I think it's neat, just from the concept itself, if it works really well, that's even better.
Thanks for the tip, Petr!