General Electric has revealed details of a potential GEN X study engine for Boeing's Sonic Cruiser concept based on a scaled compressor of the GE90-115B now in initial tests.
Admitting it is "very early days", GE90 Advanced Programme general manager Mike Benzakein says it is already assumed the GEN X will be far more integrated with the airframe than previous study engines. "On GEN X we are looking at a thrust requirement of around 90,000lb [400kN] assuming a Mach 0.98 cruise speed and a capacity of 250 passengers. This means we're looking at around an 80% scale of the GE90 core in terms of flow scale." GE "always expected" Boeing to favour an all-new engine for the Sonic Cruiser over simpler derivatives of 777 engines like the baseline GE90, and GEN X satisfies this requirement, he adds.
GE currently expects to base its GEN X concept study on upcoming tests of an evolved nine-stage high-pressure compressor (HPC) design. Based on the original 23:1 pressure ratio HPC core design developed from the joint GE/NASA energy efficient engine study, the GEN X derivative could be the eighth test core in the current series.
Tests of the fourth variant focused on three-dimensional (3D) aerodynamic improvements, while the fifth core was used to test a de-staged nine-stage configuration. The sixth core, now being tested as part of GE90-115B development, is further refining this configuration. Core seven, due to run late next year, will form the basis for a 72% scaled version for the GP7200 being developed with Pratt & Whitney for the Airbus A380.
The 80% scale version could therefore be tested as core eight as early as the end of 2003, believes Benzakein, who adds that allied HP turbine (HPT) and combustor technology development programmes are also planned to keep pace with environmental and performance demands. Advanced HPT tests are due to begin next year while a dual dome TAPS (twin augmented pre-swirl) combustor is under development for initial rig tests starting early 2002. The company believes an advanced TAPS-type combustor, based on technology first tested in the TECH56 programme, could help meet the stiff environmental requirements expected after 2006.
GE is also focused on the unusual design limits imposed by Boeing on the physical size of the fan and the area of the exhaust. The fan diameter is believed to be limited to around 2.8m (110in) diameter, with a fan pressure ratio of approximately 8:1. Although this is higher than current GE large engines, including the GE90-115B, it is being explored in a trade-off between bypass flow and noise. Traditionally, GE has maintained a relatively low fan pressure ratio to help reduce fan noise, but the long duct inlet of the Sonic Cruiser is expected to compensate for this.
Further complicating the inlet design consideration is the requirement for additional air flow during take-off and landing. The company is studying auxiliary inlet systems such as blow-in doors and panels. "It's a pretty different fan system, but it will be the core that pushes us forward," adds Benzakein.