Boeing’s confirmation in March that GE Aviation will provide the new GE9X engine to power its proposed 777X development marked the culmination of three years of preliminary work between the engine maker and the airframer in their quest to be in a position to promise a 10 percent reduction in fuel burn compared with the GE90-115B engines on the existing 777-300ER. Also promised is a 5 percent improvement in specific fuel consumption over rival widebody engines by 2020.
Now GE is looking to mature the various technologies that are expected to deliver on this promise as well as to lead to reduced noise and emissions. This phase of the program is expected to be complete towards the end of 2015 in order to have the first complete GE9X unit in ground tests during 2016, airborne in 2017 and certificated by 2018.
In an interview ahead of this week’s Paris Air Show, Bill Millhaem, general manager of the GE90 and GE9X programs, stressed that the 10 percent cut in fuel burn will be purely derived from the improved engine. GE expects to achieve additional improvements in efficiency through aerodynamic improvements in the new 777X twinjet, and especially from its enlarged composite wing.
GE’s engineers have also focused on staying ahead of the curve on tightening noise restrictions for airliners. According to Millhaem, the new turbofan has been designed with ample margin to comply with Stage 5 and CAE/10 limits. GE is working to be able to assure Boeing’s airline customers that they will be able to meet London Heathrow Airport’s tough quota count system of noise limits, including the QC/0.5 limit for arrivals and QC/1 for departures.
At the heart of the 102,000-pound-thrust GE9X engine is the new 132-inch-diameter fan (3.5 inches larger than that of the 115,000 lb-thrust GE-115B). One of its key technologies is a fourth-generation composite fan blade. Millhaem explained that the new engine’s swept, wide-chord blades will be thinner and there will be just 16 of them in the fan (compared with 22 in the GE90-115B). GE also has incorporated the lighter composite forward fan case from the GEnX development.
The rest of the GE9X architecture consists of a 3-stage booster and an 11-stage high-pressure compressor, with the first 5 stages consisting of blisks and new 3-D aerodynamics throughout. The engine’s TAPS III twin annular pre-swirl combustor is a major contributor to the improved fuel burn and reduced noise, as well as to an anticipated 30 percent reduction in NOx emissions. The new turbofan has a bypass ratio of 10.3: 1, with 27:1 pressure ratio and overall pressure ratio of 60:1. By comparison the GE90’s pressure ratio is 19:1 and that of the GEnX is 23:1.
“If we had just taken the GEnX and scaled it up to 102,000 pounds [of thrust] we would have achieved a 5 percent improvement [in fuel burn] but we wanted to deliver more and so we had to go to additional technologies,” said Millhaem. “The challenge we have technically is that with 27:1 ratio, the temperatures and pressures coming out of the combustor will be higher than anything we’ve had before.”
The change in bypass ratio alone resulted in a 2 percent improvement. Among the new technologies applied to the GE9X are ceramic matrix composite material (CMC) in the combustor and high-pressure turbine (which also features a new powdered alloy) and enhanced titanium aluminide in the low-pressure turbine airfoils.
CMC weighs about one-third of what equivalent metal parts would be to form the same task and has greater temperature capability. “The breakthrough was to take a ceramic material and give it load-accepting capability,” Millhaem explained. “It’s almost ductile like metal so that under impact it absorbs the load without fracturing. CMC allows us to reduce the weight of the engine and supporting structures while taking less cooling air out of the engine.”
Here at the Paris Air Show, GE (Hall 2A Stand C252) is displaying the GE9X’s high-pressure compressor. The company has completed assembly of the first unit and will soon ship it to its test facility at Massa in Italy.