I wondered that too and then saw this from tfa: “ "If you recall the Wankel," says Schkolnik, "they have a triangular rotor inside a peanut-shaped housing. We

I wondered that too and then saw this from tfa: “ "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.”