The concept is well known; open rotors have a much lower fuel burn, in part because of the tremendous bypass ratio. Here’s GE’s Unducted Fan engine video.
So what has SAFRAN done that’s different? Safran says that issues with noise and vibrations have been solved. Plus they are using new materials, for example, the blades are 3D woven. This makes them lighter and they are solid. This Open Rotor demonstrator was been developed under the European Clean Sky research program. SAFRAN claims the architecture of the Open Rotor will reduce fuel consumption and CO2 emissions by 30% over the CFM56.
SAFRAN has an open-air rig at Istres where the engine will be tested.