[Animats]

Axial engines go back a long way, to at least 1917.

https://en.wikipedia.org/wiki/Axial_engine

That format is widely used in hydraulic systems, and is the basis of continuously-variable hydraulic transmissions. Classically, it has problems at high RPMs, but is well behaved at low ones.

It's an idea that might be worth looking at again. With better materials and controls, it might work. The geometry is more flexible than with Wankel engines. The elegant Wankel geometry means there aren't many parameters that can be adjusted to improve combustion. In a piston engine, you can design piston face geometry, cylinder head geometry and fuel and air injection points for better combustion. With a Wankel, you're kind of stuck with the geometry. We'll have to see how this new approach works on pollution control.