Turbine Technology: The GEnx Engine

Fewer parts, quieter, and more composite materials


There are two models of GE's GEnx engine: the GEnx-1B engine which will provide power for the Boeing 787 family of aircraft, and the GEnx-2B engine which will provide power for the 747-8 aircraft. Testing of the GEnx-1B engine began in March 2006 and testing of the GEnx-2B engine began in 2008. By January 2010, the GEnx program has accumulated more than 7,800 hours and more than 10,500 cycles during testing. This included flight testing on the GE 747 flying test bed, where both of the engines have completed a combined 130 flights and more than 700 flight hours. Certification of the GEnx-1B engine occurred in March 2008 and certification of the GEnx-2B engine is planned for this year.

The two engine models share a common engine core, but do have some model-to-model differences. The GEnx–1B engine fan is 111 inches in diameter and produces about 70,000 pounds of thrust, and the GEnx-2B engine fan is 104 inches in diameter and produces about 67, 000 pounds of thrust. Another difference is that functions previously served by bleed air, now use electrical power from the starter-generators mounted on the GEnx-1B for the 787 Dreamliner. This is not the case with the –2B model engine.

The GEnx engine is designed for the engine market currently served by GE's CF6-80C2 engine, which operates on many of today's wide-body jets. GE states there will be several advantages over the GE CF6-80C2, including a 15 percent reduction in specific fuel consumption (SFC), and a 35 percent improvement in exhaust gas temperature (EGT) retention. The GEnx has 30 percent fewer parts and is planned to remain on wing 30 percent longer. GE also states this engine will be 30 percent quieter. However, the noise footprint of an aircraft powered by GEnx engines will be as much as 50 percent smaller than the noise footprint of a Boeing 767 aircraft powered by CF6-80C2 engines.

AMT spoke with Tom Walker, GEnx program manager, for a look at some of the technology used on this engine. Walker says, "The GEnx uses the same basic architecture as the GE90-115B with several new features." The GEnx employs the two-spool design (LPT-LPC-fan and HPT-HPC) and 360-degree compressor casings. Walker explains that some of the features include third-generation composite fan blades, a new composite fan case, second-generation 3-dimensional aerodynamic (3-D aero) airfoils, a new twin-annular pre-swirl (TAPS) combustor, counterrotating high-pressure and low-pressure turbines, and an advanced engine diagnostic system. Additionally, new metal alloys, coatings, and cooling technologies have been introduced in an effort to extend the life of engine parts.

More composite engine parts
As engines grow in size so do the fans and they can become heavier. The fan blades for the GEnx are manufactured using composite material that makes the blades less dense, therefore lighter in weight. The wide-chord composite fan blades have a titanium shield on the leading edge to protect them against impact damage. The number of fan blades is 18 compared to 22 on the GE90-115B and 36 on the CF6-80C2. This also reduces overall engine weight. GE says the blades are virtually maintenance-free.

The fan case is manufactured from a fiber-braided composite-matrix material. The new composite case provides better containment, is highly resistant to damage, fatigue, temperature extremes, and corrosion. "The weight savings with the composite case is approximately 340 pounds per engine," Walker says.

Walker says, "The HPC has a pressure ratio of 23:1 — the highest in the industry." The engines use blisks or blades and disks that are one part, for stage 1, 2, and 5, which eliminates any dove-tail wear on these particular units. Also, powdered alloy disks extend the lives of life-limited parts (LLPs).

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