I saw this article via a post on Allpar forums
There’s a new spin on the rotary engine.
Liquid Piston, a Connecticut-based engineering firm, has turned the classic Wankel engine design inside out to create a more efficient, and cleaner-burning motor.
The X Mini is a little powerhouse with a core that weighs just four pounds, is compact enough to fit inside a large cantaloupe, and pumps out 3.5 horsepower at 10,000 rpm. It’s envisioned as an alternative to a 50cc piston engines, but in a smaller, lighter package.
The Liquid Piston engine features a unique design that combines a roughly triangular housing, which looks something like a Venn diagram comprised of three circles, and an oval rotor. It’s basically the opposite of a Wankel layout, but Liquid Piston’s rotor also has combustion chambers built inside of it at each end. The only two moving parts are the rotor and output shaft, with intake and exhaust taking place through ports in the sides of the housing that are opened and closed by the movement of the rotor, with no valves necessary.
Company founder Alexander Shkolnik says his design allows for a different thermodynamic cycle than most internal combustion engines, and has the effect of maintaining the compression for longer than normal during combustion, then provides for overexpansion of the gasses to extract more energy out of the process.