GE Aviation has confirmed its new GE9X large-turbofan engine for the Boeing 777X incorporates a high-pressure turbine (HPT) cooling-air flow-modulation technology developed by GE and its joint-venture partner Safran Aircraft Engines for the CFM International Leap, the first powerplant to employ the HPT cooling-air modulation technique.
"It’s a good way to take advantage of really cold-air running conditions,” such as those obtained in the extended periods of low-thrust, high-altitude cruise flight in which most GE9X engines will likely spend most of their flight time, explained GE9X program manager Ted Ingling.
Like the full authority digital engine control (Fadec) computer in the Leap engine, the GE9X Fadec computer can control the amounts of bleed air diverted from the engine’s core high-pressure compressor (HPC) airflow to the cooling circuits in its HPT blades and vanes, precisely providing as much cooling-air protection over the surfaces of the HPT airfoils as needed during each phase of flight.
In the GE9X, the HPC bleed cooling air gets directed “just to the Stage 1 HPT—it feeds the inducer and the cooling circuit for each Stage 1 blade,” said Ingling. “We can alter it for specific flight conditions. It’s a way to get more cooling-air efficiency.” Moreover, by reducing the flow of HPC bleed air sent to the HPT first stage in cruise and other low-power phases of flight, more HPC core air goes into the combustor to be mixed with fuel, improving the engine’s thermal efficiency, fuel efficiency and performance.
The GE9X and Leap use Fadec-controlled modulation of HPC bleed air to send much more cooling air to the HPT airfoils when the engine runs at high-thrust, high operating-temperature power settings than when it runs at low-thrust, lower operating-temperature settings. In all commercial jet engines before the Leap, however, no modulation of HPC-derived bleed air for HPT-airfoil cooling is performed, so each HPT airfoil receives the same amount of cooling air regardless of whether the engine is operating at full takeoff thrust or at cruise or flight idle thrust settings.
Ingling also said the GE9X—whose 134-inch-diameter fan case is the largest of any turbofan engine developed to date—is the first GE Aviation turbofan engine to incorporate in its fan module structural outlet guide vanes (OGVs) made of carbon-fiber composite material. In all its previous turbofan engines GE has constructed the structural OGVs, which connect the fan case to the inner fan hub, from metal because they bear massive power loads.
Additionally, although the Leap was the first commercial-turbofan engine to use parts made of lightweight ceramic matrix composite (CMC) materials in its hot section (CFM makes the Leap’s 36-part first-stage HPT shroud assembly from CMC parts), the GE9X makes more extensive use of CMCs in its core than does the CFM International engine. GE makes all five different component types in the GE9X—the outer and inner liners in its combustor, the HPT stage 1 shroud assembly, the HPT stage 1 nozzles and the HPT stage 2 nozzles—from silicon carbide fibers embedded in a silicon carbide matrix.
The GE9X also makes extensive use of additively manufactured components. GE uses the process to make its combustor’s 28 fuel nozzles, heat exchanger and swirler, the engine’s particle separator, T25 temperature sensor (located immediately in front of its HPC module) and all the titanium aluminide blades on its six low-pressure turbine stages, according to Ingling.