It is called Liquid Piston, and promises a significant increase of the efficiency of the internal combustion engines. The design has a rotary piston and one valve that operates as both intake and outtake. The combustion chamber is designed to maintain a constant volume during the fuel combustion, thus increasing the efficiency of the engine. The engine will be lighter and quieter than today's engines. The inventors believe that within a couple of years they will have achieve a 40% efficiency. Currently, they managed to make a proof-of-concept model to operate for some 30 seconds. Worth to see the video in this link.