Probably worth mentioning LiquidPiston's new rotary engine design (which has been discussed on HN before): https://www.liquidpiston.com/how-it-works https://ww

Probably worth mentioning LiquidPiston's new rotary engine design (which has been discussed on HN before): https://www.liquidpiston.com/how-it-works https://www.liquidpiston.com/how-it-works (It's like an inside-out Wankel engine. Instead of a triangular rotor in an oval housing, it's an oval rotor in a triangular housing. The advantage is you get a more optimally-shaped combustion chamber, which ought to improve fuel economy and emissions. Also the apex seal-equivalents are easier to lubricate as they're attached to the housing rather than the rotor. They've made a few prototypes and they're working on durability.)