GE Aircraft Engines plans to build 100 GEnx engines this year and double that number next year, as the company accelerates production to meet a demand for 700 units from now through 2013. Now flying engines on the Boeing 747-8 and the 787 Dreamliner, GE–as of June 1–had built 28 GEnx-2Bs for the Boeing 747-8 and some 20 for the GEnx-1Bs for the 787. By the time the final assembly line in Durham, North Carolina, reaches peak efficiency, its maximum capacity could possibly produce more than 300 engines a year by 2015, according to GEnx program manager Tom Brisken.
Of course, exactly how many engines GE delivers and when will depend largely on Boeing’s success in reaching a production rate of seven, then ten 787s a month once it opens its second assembly line in North Charleston, South Carolina. Just as in the case of the two-year delay in the 787’s first flight, GE can only watch and wait. In the meantime, it continues to work on weight-saving efforts and a project to incorporate into the design a new low-pressure turbine early next year.
Brisken explained that, in an effort to cut weight, the company removed too many airfoils during its design of the original low-pressure turbine, thereby compromising performance. “It was a stretch for us,” Brisken told AIN. “We had done some component testing that led us down a path, but obviously Mother Nature didn’t like what she was being given so we had to put a little bit more weight back into the low-pressure turbine.” He also mentioned “a few turbine issues that you have on any new turbine until you get the cooling flows exactly right…But that’s all behind us.”
Originally certified in March 2008, the engine has continued to evolve as GE supported the program over the past two-plus years. “We didn’t go home and take a nap for two years,” said Brisken. “We’ve been working it continually so we really think we’re on the second generation of the engine. We’re going to certify all those features; we were able to take out some weight; we were able to put in better performance; we were able to improve the durability…all those things are in this vintage of engine–the second generation, if you will–and we’re very optimistic that we’re going to have a smooth entry into service.”
Speaking with AIN just before the first GEnx-powered 787 took to the air on June 16, Brisken appeared to relish the prospect of supporting Boeing on FAR 25 certification and pursuing the company’s goal to “make sure we’re never an issue in delaying a flight.” He didn’t, however, wholeheartedly embrace the notion that the delay benefited GE because it gave the company extra time to develop what Brisken termed a second generation of engine. “There’s good and there’s bad,” he said. “The bad part of it is we’re spending a heck of a lot more money than we ever envisioned that we’d have to spend on this program. But it’s always better to fix the problems in the factory before you go into service and learn from what you’re seeing on the hardware and quickly adapting to that.”
Expected to burn 7 percent less fuel and produce 30 percent less nitrous oxide (NOx) than the GE90, the GEnx is largely the product of better computational analysis tools that allowed engineers to remove airfoils from each stage of the engine. For example, the fan on the GEnx uses 18 composite blades, compared with 22 on the GE90.
Unfortunately, removing too many airfoils resulted in separated flow in the low-pressure turbine, requiring the aforementioned fix. Still, even with a more conservative approach, GE managed to make the low-pressure turbine 10 percent more airfoil efficient than that on the GE90. “But we took out about 30 percent,” said Brisken. “So we made a huge change in the low turbine, and we’re going back now to something that’s a little more conservative. It costs us some weight, but the SFC [specific fuel consumption] benefit far outweighs the weight increase.”
As of early June, 12 GEnx-2Bs had flown 375 hours during 243 flights on the three 747-8 prototypes. By the time of this week’s Farnborough airshow, the engines appeared likely to have flown more than 500 hours, based on their rate of testing of two to three times a day. Smaller than the engines used on the 787, the GEnx-2B features a 105-inch fan, compared with 111 inches on the -1B. Meanwhile, the low-pressure turbine contains only six stages, versus seven; and the -2B uses a three-stage booster rather than the four-stage unit in the 1B.
While the all-electric architecture on the 787 requires four 250-kilowatt starter generators– two per engine, weighing 250 pounds each–on the -1B, the 747-8 uses a traditional bleed-air system, pulling 10 percent of the compressor air for use by the air-conditioning and anti-icing system. The engines do share a common core; the rotating turbomachinery components on the high-pressure compressor and high-pressure turbine carry identical part numbers. “The only thing that’s different is obviously where you attach the compressor to extract the air; we call it the configurations hardware on the outside of the engine–that has to change because one is electric and one is pneumatic,” said Brisken.
Asked whether the engines on the 747-8 have performed as advertised, Brisken deferred to the airframe maker. “That’s probably best asked of Boeing. Otherwise I’ll get myself in big trouble,” he said. “I will say that you always find something on a flight test program, but to our knowledge there’s nothing that I would say is a show-stopper at all...overall, our view is they’re cranking out hours. If they had any major problems they wouldn’t be able to do that.” Brisken noted that the company will decide on whether or not it would have to change the low-pressure turbine on the -2B by the end of this year.
So far GE has sold 868 engines for the 787 program, which equates to 62 percent of the market, said Brisken. Royal Air Maroc will take the first GEnx-powered Dreamliner. Of course, with 108 Boeing 747-8s sold, GE has collected orders for four times that many -2Bs, or 432.
“We value that we’ll have an engine that will be the most economical engine from a number of characteristics, and the ones that count are fuel burn and a lower deterioration level,” said Brisken. “It’s just indicative of the design we have that allows that. The GE90 architecture that has only two spools [and] each spool is simply supported on a set of bearings and frames, so that keeps the engine very round through its operating conditions. So we think we’re going to have a fuel burn advantage over the competition, and deteriorate at a slower level, which actually increases your level of fuel burn advantage as time goes on. And we also think we’ll have a longer time on wing and we have fewer emissions.”
Featuring a twin-annular pre-swirl combustor, the design allows for a leaner fuel mixture, lower temperatures at less variation and, by extension, lower NOx emissions. With fewer temperature gradients within the combustor, the turbine will experience fewer gradients as well, making it more durable, and use less cooling air, “and we think that’s really going to drive home the lower maintenance costs of our product and longer time on wing.”
Doubts Raised Over 787 Standard Engine Interface
It seems Boeing hasn’t convinced everyone of the value of its standard engine interface feature on the 787 Dreamliner, allegedly allowing quick and cost-effective changeability between the Rolls-Royce Trent 1000s and GE GEnx-1B turbofans chosen to power the airplane. Talking to AIN, GE Aircraft Engines’ GEnx program manager, Tom Brisken, expressed some serious reservations about the feature.
“Anything’s possible, but everything below the wing is different,” said Brisken. “I’m not going to disagree with Boeing, but I’ll state it as a question: Is it really practical? Because when you talk about a pylon, a strut, a nacelle, a thrust reverser inlet and all the configuration hardware in there, that’s a lot of hardware and lots of millions of dollars. If you want to switch, you better bring your wallet.”
Boeing promoted the feature as a means to allow an operator or buyer of a second-hand 787 to fit the airplane with either manufacturer’s engines at any point in time. Such capability could conceivably help maintain residual values because lessors, for example, could offer any used 787–GE or Rolls-Royce-powered–to operators who want either engine type.
Asked if he thought anyone would make use of the so-called standard interface, Brisken didn’t mince words. “I don’t think it will ever happen,” he said.
GE Keeps Up Work on Smaller New Engines
GE Aircraft Engines has not forsaken the market for smaller turbofans. At least one of two other programs under development–the TechX–could enter service as early as 2015 on a large-cabin business jet, depending on the timing of a launch customer signing, while a program called NG34–a technology development effort involving the immensely successful CF34–would ready GE’s bid to power the next generation of regional jets.
Expected to cover the next generation large cabin business jets in the 10,000- to 20,000-pound-thrust range, the TechX engine draws on the latest technologies from existing engine programs, such as the low-emission TAPS (twin annular premixed swirl) combustor from the GEnx and the latest Fadec technology from the F136 engine for the JSF. Some of the features of the TechX engine include:
• GE’s new eCore, which features a high-pressure-ratio compressor in the 20:1 class range, advanced materials, unique cooling technologies, next generation TAPS combustor for efficient, cleaner fuel combustion and lowest NOx, third-generation 3-D aerodynamic design airfoils and a two-stage high-pressure turbine.
• Advanced clearance control in the turbine in which the Fadec controls the air to maximize efficiencies.
• A so-called Slimline nacelle to minimize drag and improve component accessibility, with the Fadec in the nacelle for a cooler environment and easier access for maintenance.
Claimed benefits of the TechX include 20-percent lower fuel consumption, 40-percent lower emissions, a stall-free design, no throttle restrictions and a similar core to those used in the proven CFM56 and CF34 turbofans.
Meanwhile, GE’s aspirations for a successor to today’s CF34 appear just as lofty. Again, NG34 technology centers on a low-emission core, called eCore, expected to offer 15- to 20-percent better specific fuel consumption than today’s CF34 engines. CFM will use the same core on the Leap-X, while GE borrows the technology for the TechX as well. The first eCore completed Phase 1 testing earlier this year and the company has begun Phase 2 testing. The tests center on the turbine and combustor.
Unlike in the GEnx, the fan would consist of solid titanium rather than composite. GE has determined that the extra thickness needed for a small composite fan capable of passing bird ingestion tests would increase the weight to the point of negating any benefit of using nonmetallic material. Like the GEnx and TechX, however, the new CF34 would use TAPS combustor technology, allowing pressure ratios to exceed 20:1. The TAPS combustor also results in 50- to 60-percent lower NOx emissions compared with CAEP 6 limits, and 10- to 15- EPNdb margin to Stage 4 limits.
As designers raise the pressure ratio and temperature in the core, they also need to improve the efficiency of the turbine. Turbine blades would use what GE calls the latest design advances to improve aerodynamics. Rig testing on the new design is to happen within the next two years.
As in the case of the current engines, GE would most likely supply the entire propulsion system for the next-generation CF34 engines. A nacelle integration team now works with the NG34 development teams as GE considers the use of composites as well methods to better integrate the engine and nacelle.
The new CF34 engine would occupy a thrust class between 14,000 and 18,000 pounds–a range similar to that of today’s CF34-8 and CF34-10 engines.