LiquidPiston’s X Engine is a non-Wankel rotary embodiment of the company’s innovative High Efficiency Hybrid Cycle (HEHC). The X Engine has few parts and three combustion events per rotor revolution, resulting in tremendous power density.
See also https://www.youtube.com/watch?v=PtDXNEn-hFA
Inventor Alexander Shkolnik
They are claiming 50% thermal Efficiency.
BEAT THAT STIRLING ENGINES !
http://liquidpiston.com/
Let me see your design for getting 2 HP from a 5" diameter Engine on pump gas
آی-ویدئو