Turbine Technology: The GEnx Engine

Fewer parts, quieter, and more composite materials

The engine has a twin annular, pre-swirl (TAPS) combustor which enables the fuel-air mixture to burn at a significantly lower temperature. This will minimize the formation of nitrogen oxide (NOx) and also carbon monoxide, unburned hydrocarbons, and smoke. The reduction of peak temperature variations will extend the life of the combustion liner and the turbine components downstream. In addition, the lower temperatures reduce liner cracking and eliminate the need for dilution holes and the stress concentrations they engender.

GE states the counterrotating HPT and LPT have proven more efficient than a unidirectional turbine in rig tests and in engine and flight-testing of earlier GE engines. In the GEnx engine, next-generation 3-D aero vanes, with contoured end-walls, are stated to enhance this efficiency. Walker says, "The parts count of the counterrotating turbine is reduced, and state-of-the-art cooling techniques minimize the cooling air requirement." New HPT shroud material increases hot corrosion resistance by 50 percent.

Environmental benefits
In the case of a twin-engine aircraft with GEnx engines installed, when the weight avoidance of the engine installation hardware is factored in, the savings due to the use of advanced composites and part reduction will exceed 800 pounds. This has a direct effect on the reduction in SFC, which also means more range or better payload. Reduction in harmful NOx will be approximately 40 to 50 percent, and fewer fan blades and a lower fan speed make for a quieter engine.

What about maintenance?
In an effort to reduce foreign object debris (FOD) damage and blade erosion, the engine is designed to direct much of the foreign matter entering the fan into the bypass air stream. The fan spinner also directs debris into the air stream while some smaller particles pass into the air stream through the variable bypass valve (VBV) doors.

Access to engine mounting bolts has been made easier for engine removal and replacement. A reduction in the use of safety wire is seen on the GEnx, and is not required on certain items such as borescope plugs, line replaceable units (LRUs), and fuel nozzles. Replacement of certain LRUs will only require a leak check.

The integral diagnostic capability of the engine provides the maintenance crews access to data that assists with troubleshooting and ultimately timely maintenance actions. The system captures data for many items such as fuel system trending and fault isolation, bearing degradation trending, lubrication oil filter replacement prediction, starter/ignition system deterioration, vibrations, modular performance, gas path anomalies, and improved fault isolation for LRUs.

Walker says, "At the module level we have maintenance in mind." The modular design of the engine is such that when extensive maintenance of the propulsor is required, the fan assembly can be separated from the propulsor, the propulsor can then be sent to a maintenance facility for repair work and the fan can be returned to service and installed on another propulsor.

To date GE has developed more than 80 individual repair procedures for the GEnx with a focus on line maintenance and module level maintenance. GE is developing an additional 85 repairs, including repair procedures that are focused on piece-part level repairs that will be required at the first restoration shop visit. GE plans to proactively continue repair development on the engine well into its life cycle.

GEnx training
Computer-based and hands-on line maintenance training on the GEnx-1B engine have been underway at the Customer Technical Education Center (CTEC) located in Cincinnati, OH, for approximately six months. Last month GE began computer-based and hands-on line maintenance training for the GEnx-2B engine customers. Students will have the opportunity to take basic line maintenance training via computer-based digital video discs (DVD) or via the Internet.

Hands-on training such as line maintenance, engine change, and borescope inspection is instructor lead at the CTEC with classes lasting from two to five days. Entry into service training is approximately two weeks in length. During 2009 about 160 students attended the GEnx-1B course, the majority being internal GE Aviation employees such as field service engineers and a few GEnx-1B customers. This year, more training is planned, with most customers sending their employees to training about six months before the engine enters into service for the operator.

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