General Electric GEnx

GEnx on 747-8I prototype

The GEnx and the Rolls-Royce Trent 1000 were selected by Boeing following a run-off between the three big engine manufacturers. The GEnx uses some technology from the GE90 turbofan,[1] including swept composite fan blades and the 10-stage HPC featured in earlier variants of the engine. The engine carries composite technology[2] into the fan case.

The engine market for the 787 is estimated at US$40 billion over the next 25 years. A first is the elimination of bleed air systems using high temperature/high pressure air from the propulsion engines to power aircraft systems such as the starting, air-conditioning and anti-ice systems. Both engines enable the move towards the More Electric Aircraft, that is, the concept of replacing previously hydraulic and pneumatic systems with electrical ones to reduce weight, increase efficiency, and reduce maintenance requirements.

The GEnx was expected to produce thrust from 53,000 to 75,000 lbf (240 to 330 kN) with first tests commencing in 2006 and service entry by 2008 (delayed by 787 deliveries). Boeing predicts reduced fuel consumption of up to 20% and significantly quieter engines than current turbofans. A 66,500 lbf (296 kN) thrust version (GEnx-2B67) will be used on the 747-8. Unlike the initial version, for the 787, this version has a traditional bleed air system to power internal pneumatic and ventilation systems. It will also have a smaller overall diameter than the initial model to accommodate installation on the 747.

General Electric began initial test runs of the bleedless GEnx variant on 19 March 2006.[3] The first flight with one of these engines took place on 22 February 2007, using a Boeing 747-100, fitted with one GEnx engine in the number 2 (inboard left hand side) position.

By Fall 2019, General Electric was offering the GEnx-2B, developed for the 747-8, for the revised 767-XF variant based on the 767-400ER, but needed enough volume to cover the new product certification.[4]

Introduced in late 2011 on a 747-8 freighter, Cargolux surpassed one million flight hours in early 2017.[5] In the summer of 2012, three engines suffered Low Pressure Turbine (LPT) failures. One failure was caused by an assembly problem, which led to inspections of all other engines then in service.[6]

During the spring and summer of 2013, GE learned of four 747-8F freighters that suffered icing in their engines at altitudes of 40,000 feet and above. The most serious incident involved an AirBridgeCargo freighter; on July 31, while at an altitude of 41,000 feet over China, the flight crew noted two engines surging while a third lost substantial power. The pilots were able to land the plane safely but the engines were found to have sustained damage. Among the possible factors cited was "'unique convective weather systems' such as unusually large thunderstorms reaching high altitudes." Boeing is working with GE on software solutions to the problem.[7] Altitude was restricted until GE changed the software to detect the high-altitude ice crystals and open bleed air valve doors to eject them before they enter the core.[5]

The GEnx-1B installed on the 787

In March 2014, a GEnx-powered Boeing 787 had its first in-flight shut down in operation when a JAL flight had to divert to Honolulu after an oil pressure alert, bringing its in-flight shut down rate to 1 per 278,000 hours.[8] In January 2016 a Japan Airlines 787 had an inflight shutdown after flying through icing conditions, caused by ice formed on fan blades and ingested: the blades moved forward slightly and rubbed on the abradable seal in the casing.[5] In March 2016, the US FAA ordered emergency fixes on the GEnx-1B PIP2.[9] The airworthiness directive affects 43 Boeing 787 Dreamliners in the US.[10] Abradable material in the casing in front of the fan blades was ground to keep them from rubbing when ingesting ice or debris on 330 GEnx PIP-2.[5]

In early 2018, of 1277 orders for the B787, 681 selected the GEnx (53.3%), 420 the Rolls-Royce Trent 1000 (32.9%) and 176 were undecided (13.8%).[11] The 2,000th GEnx was delivered by November 2019, 15 years after the engine launch, as it logged 4.5 million flight cycles and 26 million hours among 60 operators.[12]

Fan blades and inlet guide vanes of GEnx-2B

Detail of GEnx core

The GEnx is derived from the GE90 with a fan diameter of 111.1 in (282 cm) for the 787 and 104.7 in (266 cm) for the 747-8. To reduce weight, it features 18 composite fan blades, a composite fan case and titanium aluminide stage 6 and 7 low-pressure turbine blades. Fuel efficiency is improved by 15% compared to the CF6, the bypass ratio reaches up to 9.0:1 and the overall pressure ratio up to 58.1:1. It has a 10 stage high-pressure compressor and is quieter, helped by larger, more efficient fan blades.[13]

It stays on wing 20% longer, uses 30% fewer parts to lower maintenance costs and has a contra-rotating architecture.[14] The Lean TAPS combustor reduces NOx gases with required pressure loss and backflow margin.[15]

Fan blades have steel alloy leading edges and the composite fan case reduces thermal expansion. To reduce fuel burn, the 23:1 pressure ratio high-pressure compressor is based on the GE90-94B, shrouded guide vanes reduce secondary flows and counter-rotating spools for the reaction turbines reduce load on guide vanes.[16]

To reduce maintenance cost and increase engine life, spools with lower parts count are achieved by using blisks in some stages, low blade counts in other stages and by using fewer stages; internal engine temperatures are reduced due to more efficient cooling techniques and debris extraction within the low-pressure compressor protects the high-pressure compressor.

• Boeing 747-8
• Boeing 787 Dreamliner

Related development

• General Electric GE90
• General Electric GE9X

Comparable engines

• Engine Alliance GP7000
• Rolls-Royce Trent 1000
• Rolls-Royce Trent XWB
• Rolls-Royce Trent 7000

Related lists

• List of aircraft engines

Wikimedia Commons has media related to General Electric GEnx.

• Official website
• "General Electric's GEnx-1B engine for the Boeing 787 makes first flight on 747 testbed". Flight International. 23 Feb 2007.
• "GE plans mid-July nod for GEnx siblings". Flight International. 16 June 2010.