Story ID: 549
GE9X Speeds Toward Latest ‘Toll Gate’
By: Gregory Polek
Caption: The new GE90 for the Boeing 777X will be 10 percent more efficient than current models, thanks to new materials currently under test.
Word Count: 1008
Development of the GE9X turbofan for Boeing’s new 777X widebody has shown no sign of slowing, as engineers at GE Aviation (Chalet 142) prepare the all-new 100,000-pound-thrust-class behemoth for what the company calls Toll Gate 6.

Speaking with AIN recently, GE Aviation’s general manager of the GE9X and GE90 programs, Bill Millhaem, described the milestone as the point at which the company defines the configuration it will use in the certification program. Scheduled for certification by the end of the third quarter of 2018, the engine has shown “no issues” that might threaten to derail its progress, said Millhaem, thanks in large part to the long lead times GE has given itself for refining the various technologies and design elements needed to deliver its promised 10-percent fuel-burn advantage over the Boeing 777-300ER’s GE90-115B.

Part of the fuel-burn improvement will come from what GE advertises as the highest pressure ratios among any commercial engine in production; the 9X design calls for a 60:1 overall pressure ratio and a 27:1 pressure ratio in the high-pressure compressor. Of course, higher pressure ratio means a higher operating temperature in the back of the compressor and high-pressure turbine, necessitating the development of new nickel-based disc alloys and ceramic matrix composites (CMCs) for the inner and outer combustion liner, the Stage 1 high-pressure turbine shroud and the Stage 1 and 2 high-pressure turbine nozzles.

“[The CMCs] are in an engine running right now–a GEnx engine–sized for a GEnx but in a configuration designed for the GE9X,” said Millhaem. The design of the 9X calls for the most extensive use of CMCs ever by GE Aviation, which also uses the material in the high-pressure turbine shroud on the Leap engines under development with its CFM partner, Snecma.

“CMCs are now ready for prime time,” said Millhaem. “I would say we are working on scale now.” A new plant GE opened last October in Asheville, North Carolina, for mass production of the CMCs in the Leap engine will also serve as the supplier for 9X CMCs.
Big 16-Blade Fan
In the fan, GE has reduced the number of blades from 22 in the GE90-115B to 16 in the 9X while increasing the fan diameter from 128 inches to 134 inches, thereby improving bypass ratio and the overall propulsive efficiency of the engine. To allow for fewer fan blades, GE developed a next-generation composite material and a stainless steel, rather than titanium, leading edge. Both changes increase blade strength, allowing GE to make them wider, longer and thinner to improve airfoil efficiency. GE plans to run its first fan blade-out test in the first half of 2016.

“This is really our fourth-generation composite fan blade,” said Millhaem. “We just passed 50 million hours of operating experience on the GE90, so we’re well over 50 million hours when you throw in the GEnx blades as well.”

Over the past year GE completed trials on a one-fifth-scale fan at Boeing’s universal propulsion simulator (UPS) cell in Seattle, where the engine company tested performance, acoustics and crosswind operation. “That’s part of our whole strategy on the engine, which was to really mature the technologies well in advance of the certification program,” noted Millhaem. “Basically, every one of the technologies that we’ve either improved on or are introducing on the GE9X will have gone through a maturation and demonstration program…they basically have to win their way onto the final design.”

One of the other key characteristics of that design centers on the high-pressure compressor, a 90-percent-scale test version of which ran at GE’s Avio Aero subsidiary in Massa, Italy, where engineers completely mapped the operating envelope and identified stage-to-stage loading, for example. It has since taken apart the compressor for inspection, put it back together with “some enhancements” in the front end and returned it to Italy for more testing. The HPC has now accumulated more than 350 hours of testing, said Millhaem. “So far the data has exceeded our expectations and we’re well on our way to finalizing the design,” he reported.

Changes in the compressor from the GE90 include an increase in the number of stages from nine to 11, leading to the boost in pressure ratio. “I think the big advance is we have improved tools to develop the high-pressure compressor airfoils; [and] we’ve introduced the concept of super-polishing the airfoils, which improves the surface finish and gives us better performance at the individual airfoil level,” explained Millhaem. The increase in pressure ratio from 19:1 to 27:1 has raised the HPC’s operating temperature by around 100-degrees C, requiring a new powdered metal disc alloy to be used both on the back of the HPC rotor and on the front of the high-pressure turbine.

The 9X’s higher temperatures, pressures and flow rates have also led to new advances in GE’s TAPS combustor, on which the company has run single-cup tests with the new higher operating parameters in a new $100 million facility in Cincinnati. Having now almost finished commissioning the facility, GE plans to perform similar testing on what Millhaem described as a one-quarter or 90-degree sector of the GE9X combustor. “[This will] allow us to not only to understand how the individual burner operates, but also to look at the dynamics and the transience as you change fuel flow and power requirements, and how the cups interact with each other,” he explained.

GE is not expecting to run the CMC trials on its GEnx test article until some time in early summer, and plans to run a core engine that is currently under assembly in the second half of this year, before running its first full turbofan engine in the first half of 2016. Testing of that engine will represent the final phase of GE’s technology maturation program, said Millhaem, allowing the company to finalize certification configuration before flying the first test-bed mounted engine in the middle of 2017.