General Electric has revealed that its Passport 20 engine, destined for the Bombardier 7000 and 8000 ultra-long range business jets, will be partly made using a new form of ceramic matrix composite material, with a wide range of potential applications in the aviation industry.
The disclosure by GE on 1 October of the oxide-oxide CMC material in the 16,500lb-thrust (75kN) Passport 20 adds another key data point in the company’s product strategy.
GE is investing billions to develop new materials that are lighter and can survive in hotter temperatures. Such materials allow designers to eliminate the elaborate cooling systems that are necessary to prevent metals inside the engine from melting, but reduce fuel efficiency.
The oxide-oxide CMC material replaces what would have been graphite-epoxy components in the Passport 20 – namely, the four-piece panel enclosing the engine core and a nine-piece component called a mixer, says Judd Tressler, director of Bombardier programmes for GE.
The latter is stationed in the exhaust flow of the engine and is designed to minimise pressure losses and reduce noise as the bypass air flow mixes with the heated exhaust air.
The new oxide-oxide material saves 18.1-20.4kg (40-45lb) in the mixer components alone. The material is one of several new technologies on the Passport 20, including a 132cm (52in)-diameter fan blisk and “super”-finish airfoils, allowing GE to claim an 8% specific fuel consumption advantage over the Rolls-Royce BR725.
GE has been developing oxide-oxide CMC for more than 20 years. In fact, the company quietly deployed the material early in the last decade. The US Navy acquired the GE technology to increase the endurance of the mixer on the F414 engine that powers the Boeing F/A-18E/F Super Hornet.
The manufacturer next selected oxide-oxide CMC for the Passport 20 engine in late-2010, with the goal of helping to reduce overall weight for the engine. The oxide-oxide material is now the second form of CMC known to be in development on GE engines.
A silicon-carbide (SiC)-based CMC material, which can survive even hotter temperatures than oxide-oxide, is being developed for CFM International Leap powerplants. The SiC-based material replaces specialty metal alloys in the first stage high-pressure turbine shrouds – one of the hottest parts of any turbofan.
The Leap-1A engine enters service on the Airbus A320neo in 2015. Meanwhile, GE is already transferring the SiC-based CMC to the GE9X engine for the Boeing 777X, but expanding its use to the first stage turbine blades and the combustor lining.
Likewise, GE is also looking to expand the use of oxide-oxide CMCs to other commercial turbofan engines – possibly including the GE9X, in similar regions of the engine as the Passport.
“I don’t see anything that would keep us from scaling it [to a bigger engine],” says Bernie Renggli, a principal engineer for GE.