General Electric is expecting near simultaneous regulatory certifications for its GEnx-1B and -2B engines in July, several months ahead of the planned certification and service entry for the Boeing 787 and 747-8.

Beyond the approvals, GE is gearing up to build 700 engines of the two types for 28 customers by the end of 2013 based on current backlog.

The two engines have a common core, with 10 high-pressure compressor (HPC) stages, lean-burn combustor and two high-pressure turbine (HPT) stages.

"We will recertify all improvements [to the -1B] in July," says GEnx programme manager Tom Brisken. "Meanwhile, testing is complete on -2B and certification reports have been submitted." GE had initially gained US Federal Aviation Administration certification for the -1B engine in March 2008, but durability and operability issues with the fuel nozzles in the lean-burn combustors and the advent of delays in the 787 programme gave GE time for a redesign that must now be recertificated.

Brisken says the results of a recent 1,000-cycle intermediate maintenance interval test show that the new design "solved all the issues" and provided "excellent" durability.

Changes to the combustor design were needed to manage what would have been increased nitrogen oxide emissions in the presence of fuel-saving increases in pressure and temperature in the core. Brisken says the lean-burn technology results in 150-205e_SDgrC (300-400e_SDgrF) lower temperature in the combustion chamber compared to a conventional combustor, which results in less NOx produced. "We never get to the stoichiometric temperature that generates the emissions," says Brisken.

Boeing has begun initial ground-testing of the GEnx-1B, which is the Dreamliner's second engine option after the already certificated Rolls-Royce Trent 1000, on its fifth 787 test aircraft (ZA005). Test aircraft ZA006 will also be powered by the 75,000lb-thrust (334kN) GEnx, which has a 282cm (111in) fan diameter and 9.6:1 bypass ratio, GE's highest bypass ratio engine to date.

Delivery of the first GEnx-1B-powered 787 to Royal Air Maroc is due late this year or early in 2011, following the handover of the first R-R-powered 787 towards the end of this year to launch customer All Nippon Airways.

While the GEnx-1B has two 250kW generators on each engine for the 1MW more-electric systems on the 787, including the engine starter, the -2B carries traditional pneumatic systems for starting and for environmental controls.

The 66,500lb-thrust engine has a 267cm fan diameter and bypass ratio of 8.6:1. While the cores are the same, the booster stage forward of the core for the -2B engine is three stages rather and the low-pressure turbine downstream of the core is six stages instead of seven. GE is the sole provider of engines for the 747-8 in both the passenger and freighter configurations.

By early June Boeing had accumulated 1,500 operating hours on the -2B engines in the three-aircraft 747-8 test fleet. A fourth test aircraft, belonging to launch customer Cargolux, will enter the test programme in late July. Certification and first delivery of the cargo version of the aircraft is expected in the fourth quarter.

Upgrades to the -1B engines are also under way ahead of service entry. Brisken says a performance improvement package that will put additional blades in low-pressure turbine (LPT) module to improve aerodynamics will begin ground- and flight-testing on GE's 747 testbed this summer and be ready for a block upgrade introduction on the 787 in the third quarter of 2011.

Engineers had originally designed the -1B with 30% fewer LPT blades compared with the 777's GE90, but learned during development testing that it had removed too many. "Mother nature said we went a little too far," says Brisken. Even with the block upgrade, however, the -1B will have 10% fewer blades than the GE90.

Beyond that, Brisken says a mid-life upgrade for the engines may include ceramic matrix composite blades in certain sections that will further reduce weight and increase life.

Source: Flight International