CMCs will be used for inner and outer combustor liners, high-pressure turbine nozzles, first-stage shroud and uncooled second-stage blades. “We are doing testing to determine their feasibility,” Millhaem says. “We will run CMCs in 2014 in GENx demonstrator engines,” says Fitzgerald.
CMCs are a third the weight of high-temperature superalloys, have two times the strength and 20% greater temperature capability, reducing the cooling air required, Millhaem says.
Use of CMCs in the hot section accounts for another 2% fuel-burn reduction. GE has a back-up plan “that will keep the impact relatively small,” he says, if CMC blades prove not to be workable.
Titanium-aluminide blades will be used in the low-pressure turbine. Additive manufacturing is being looked at for fuel nozzles, where it is used in the smaller General Electric/Snecma Leap-1. The GE9X will have a so-called TAPS 3 combustor, rebalanced for the higher pressure and temperature of the air from the HPC.
“We are looking at active clearance control in the engine and evaluating other new technologies,” says Millhaem, stressing that everything in the engine “will be at TRL 6 [technology readiness level] and MRL 6 [manufacturing readiness level] at tollgate 6 [design freeze in 2015].”
The first full core engine is planned to run in 2015, and the first full engine in 2016. The GE9X is scheduled to get airborne on a GE flying test bed in 2017, with certification planned for 2018.
GE has “no plans” to put GE9X technology back into the GE90, but because it will first test the changes in GENx demonstrators, the experience “will allow us to define ways to take technologies back into the GENx,” says Fitzgerald.