The US Air Force Research Laboratory has awarded up to $325 million to GE Aviation to continue working on adaptive cycle engine technology as new data emerges from the ADVENT programme.
The latest award announced on 20 January falls under phase three of the nearly 10-year old versatile affordable advanced turbine engines (VAATE) programme, which includes ADVENT.
GE collected more than 100 hours of combined test data from a core rig two years ago and full ADVENT engine last year. The Air Force Research Laboratory (AFRL) will complete an assessment of the GE data in February.
GE believes the results of the core and full engine tests show that a follow-on demonstrator engine – the adaptive transfer engine demonstrator (AETD) and a future production engine will meet the US Air Force’s performance goals.
The testing included “multiple stable conversions” from high-bypass to low-bypass operation, GE says. That means no other company has yet achieved a “successful demonstration of an adaptive cycle engine”, GE adds.
In a normal turbofan engine, a small amount of air enters the core and is mixed with fuel for combustion, while another, larger stream of air flows around the core and generates thrust more efficiently. An adaptive turbofan adds another channel of bypass air, which is opened during cruise and closed during take-off or to accelerate quickly.
That third stream of air can improve the range of a platform by 35%, GE says.
The core and full rig tests also validated another benefit of using a third stream. A stealth aircraft, such as the Lockheed Martin F-35, cools electronics bays by channeling heat into the bypass duct. An adaptive cycle engine raises the capacity of the bypass air to serve as a heat sink. The additional air stream reduced bypass duct temperatures by about 65°C in the test engine compared to the F136 engine developed for the F-35, GE confirms.
The ADVENT programme also helped GE collect data on how new engine materials, such as ceramic matrix composites (CMCs), perform at extremely high temperatures.
GE is using CMCs to replace largely nickel-based alloys in the hottest sections of military and commercial turbine engines.
The ADVENT engine featured CMCs on the leading edge of the high-pressure turbine nozzle, where gases released from the combustor flow into the rotating turbine section.
The leading edge of the turbine nozzle was exposed to temperatures hotter than 1,650°C (3,000°F) – or hundreds of degrees hotter than the melting point of nichel-based materials – during the tests, but survived, GE says.