Under the European Clean Sky programme, research conducted has shown that short- to medium-range aircraft with counter-rotating open-rotor engines is technically feasible. Design studies have shown open-rotor engines to be the best candidates for low fuel consumption and pollutant emissions. The next hurdle is to develop new technologies and advance the maturity of the open rotor as a possible successor to the turbofan engine. Researchers working on the EU-funded project ABAG (Power gear box (PGB) advanced planet bearings development) proposed a cutting-edge design for the planetary gear system. A planetary gear system is incorporated in the open rotor to connect the turbine output shaft and fan rotors and allow the turbine and fan rotors to operate at the optimum speed. The open rotor gear system is required to be lightweight and highly reliable. To date, engines and their main components such as gear boxes relied on traditional rolling element bearings of steel. The ABAG project team explored new materials to improve the surface and near surface robustness in contact areas of bearing systems under extreme engine conditions. Specifically, two different materials were selected for an extensive test campaign. Ferrium C61, a new high-strength steel and M50NiL-DH. These state-of-the-art materials for aerospace bearings were treated using gas carburising, vacuum hardening, plasma and gas nitriding and their final properties were analysed. Endurance tests were performed under low lambda conditions, similar to those that occur during open rotor operation. Next, spall propagation was tested in just M50Nil-DH, because the results obtained in the endurance testing of Ferrium C61 were not satisfactory. The ABAG test campaign significantly improved material properties by optimising the parameters of surface engineering processes. While some technologies can be assessed during the development phase of the open rotor engine, the true potential of key technologies has already been validated.
Aircraft engine, Clean Sky programme, counter-rotating open-rotor engine, planetary gear system, bearings, M50NiL-DH