World's largest commercial aircraft engine fired up for the first time

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Ground testing is underway on the first full GE9X development engine(Credit: GE Aviation)

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The world's largest commercial aircraft engine has been started up for the first time at GE Aviation's Peebles Test Operation in Ohio. According to GE, ground testing of the GE9X development engine will enable data to be gathered on the engine's overall and aerodynamic performance, mechanical verification, and aero-thermal system validation leading up to flight testing and certification before entering service at the end the decade.

With a front fan spreading a full 11 ft (3.35 m), the GE9X is a world record holder and generates thrust in the order of 100,000 lb. To accommodate the aeronautical behemoth, the Peebles facility was recently upgraded with a larger air intake, extra fuel tanks to feed the giant engine, and high temperature gear to deal with the hotter, more efficient design.

GE says that the GE9X is currently undergoing its first Full Engine To Test (FETT). This is the next level of the test series, which began in 2011 at the component level, and marks the first test of the complete system, which comes only six months after the engine design was finalized. GE says that this relatively early testing was to ensure that the test data was available as soon as possible for the certification engines, which are scheduled to be installed in GE Aviation's flying test bed for certification of flight testing in 2018.

Developed for the 777X airliner, there are over 700 GE9X engines on order at an estimated value of US$29 billion. It features a composite fan case containing 16 fourth-generation carbon-fiber composite fan blades, which push air into an 11-stage high-pressure compressor with a 27:1 pressure ratio. Weight is saved by the extensive use of ceramic matrix composites (CMC), which allows the combustor and turbine to handle temperatures of up to 2,400º F (1,315º C) for greater fuel efficiency and lower emissions.

In addition, the GE9X incorporates 3D-printed fuel nozzles, the complex architecture of which has not been made public by the company.

"These tunnels and caves are a closely guarded secret," says GE Aviation spokesman Rick Kennedy. "They determine how the fuel moves through the nozzle and sprays inside the combustion chamber."

To harness the power of the engine, the GE9X is equipped with a low-pressure turbine module and the Accessory Drive Train (ADT) kit, which regulates the unit and distributes its energy for secondary functions by means of an inlet gearbox, transfer gearbox, and Accessory GearBox (AGB).

The latter powers the fuel pump, oil pump, hydraulic pumps for the flight controls, an air turbine to start the engine, and other onboard systems, yet has 10 axles and nine accessories as opposed to the previous GE90, which has 11 axles and only eight accessories. In addition, the AGB has a small fuel adapter for a simpler external pipe system and an improved engine profile.

"The reduction in the number of axles not only benefits weight, but also reduces the part count and simplifies the supply chain," says Rocco Pellettieri, project engineer for the GE9X at Avio Aero. "The design with fewer axles but more accessories compared to the GE90 was made possible thanks to complex optimization studies that allowed us to achieve more with less."

GE says that a second engine will be ready for testing next year and that the GE9X is scheduled to enter service around 2020.

The video below shows the initial start up of the GE9X.

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