Ceramic matrix composites (CMCs) are being introduced into aircraft engines because of their ability to resist heat, as well as their ability to resist dust and debris in difficult environments, such as those in the Middle East. Although CMCs have been utilized on military aircraft engines, GE is pioneering the use of CMCs on commercial aircraft with the GE9X for the 777X. The GE9X, which will be used on the Boeing 777X, has a larger diameter than the fuselage of a Boeing 737.
What is a CMC? CMC parts are made from silicon carbide ceramic fibers aligned in a ceramic matrix that are then covered with a proprietary heat-resistant coating — essentially a ceramic fiber reinforced ceramic. These lightweight components, which have one-third the density of typical metal alloys, are more heat resistant and require less cooling air. This enables higher temperature operations and increased thermal efficiency for an engine, leading to better fuel economy.
GE is using CMCs in several areas of the “hot section” of the engine. The big application is for combustor liners, which is the area in which fuel is burned and the hottest portion of an engine. They are also used in High Pressure Turbine (HPT) stage 1 shrouds, and HPT nozzles for stages 1 and 2. The HPT is just after the combustor, and experiences high heat as hot gasses pass through the engine.
GE has now completed more than 4,500 cycles over two testing phases, the second of which just successfully concluded, on its GEnx demonstrator engine. (That engine is currently used on the Boeing 787 and 747-8.) In addition to the new CMC parts, that demonstrator engine also incorporated the latest advancement in additive (3D) manufactured titanium aluminide (TiAi) blades produced at Avio Aero, and next generation HPT stage 1 blades with advanced cooling technology. These technologies combine to generate a significant improvement in fuel efficiency, and all will be used on the GE9X.