We've written a few times before about the fascinating LiquidPiston rotary engine. It's not a Wankel – indeed, it's closer to an inside-out Wankel – and with only two moving parts, it's able to deliver extraordinary power density at up to 1.5 horsepower per pound (0.45 kg).
According to co-founder and CEO Alec Schkolnik, the X Engine design combines the high compression ratio and direct injection of a diesel engine with the constant volume combustion process of an Otto cycle engine and the over-expansion abilities of an Atkinson cycle engine, while solving the lubrication and sealing issues of the Wankel rotary engine and delivering huge power and efficiency. Check out the design being used in a go-kart and an unmanned aircraft in the video below.
"If you recall the Wankel," says Schkolnik, "they have a triangular rotor inside a peanut-shaped housing. We have the opposite, a peanut-shaped rotor in a tri-lobed housing. So take everything you know about the Wankel and turn it literally inside out. They have a long, skinny, moving combustion chamber, we have a stationary combustion chamber that's nice and round. You can drive it to a high compression, just by making the chamber smaller. And because it's stationary, we can directly inject fuel where the Wankel could not. So those are the two key advantages of the diesel: high compression ratio and direct injection.
"And then there's our apex seals, they're like our piston rings," he continues. "In the Wankel engine, they're inside the rotor, again. They move at a high speed, and bounce around, they're very hard to lubricate. In our case, they're stationary, they don't bounce around, and you can lubricate them directly from the housing.