The LiquidPiston engine can be considered as a Wankel turned inside-out then greatly improved. Much lighter for the output and easily double/treble the efficiency. Will debut in the UAV market as well as a range extender application.
https://www.sae.org/news/2018/03/x-marks-the-spot
Nice animation demonstration of the LiquidPiston in operation:
http://liquidpiston.com/technology/how-it-works/