wow, very cool. Throughout the years, I have thought of a bunch of different ways to develop a new kind of engine with less parts but I never thought of somethinglike that. It sounds like a great idea.
Yup, they have been around for a while. A lot of automotive A/C compressors are built the same way. The difference is that they are driven by a belt and used as a pump. When you boil it down an engine is just a self-powered air pump anyway.
I think in the past they have had a history of sealing and longevity problems. But with today's technology who knows? It's interesting that it has a 2400-2500 PRM red line and big torque numbers like a diesel.
If the fuel economy and manufacturing cost make sense, it looks like it might make a good boat engine.