"Superjet" variable cycle jet engine could power future fighter aircraft
GE Aviation is developing a revolutionary new jet engine that aims to combine the best traits of turbojet and turbofan engines, delivering supersonic speed capability and fuel efficiency in one package.
The new engines are being developed under the USAF ADVENT project, which is seeking 25 percent fuel saving which will in turn lead to an increase in mission capability.
There are two main species of jet engines for aviation: low-bypass turbofans, usually called turbojets, and high-bypass turbofans. Turbojets are optimized for high-performance, pushing fighter jets to above Mach 2 (and the SR-71 "Blackbird" to well over Mach 3), but pay for that performance with terrible fuel efficiency. The performance outcome of a conventional turbojet is dominated by the operation of the high-pressure engine core (compressor, combustion, turbine, and exhaust nozzle).
In contrast, high-bypass turbofans are the heavy lifters of commercial aviation, being optimized for subsonic thrust and fuel efficiency, but performing poorly at supersonic speeds. A conventional turbofan adds lower-pressure airflow from an oversized fan which is driven by the jet turbine. The fan airflow bypasses the combustion chamber, acting like a large propeller.
In an ADVENT (ADaptive VErsitile ENgine Technology) engine, the high-pressure core exhaust and the low-pressure bypass streams of a conventional turbofan are joined by a third, outer flowpath that can be opened and closed in response to flight conditions. For takeoff, the third stream is closed off to reduce the bypass ratio. This sends more of the airflow through the high-pressure core to increase thrust. When cruising, the third bypass stream is opened to increase the bypass ratio and reduce fuel consumption.
The extra bypass duct can be seen running along the top and bottom of the engine. This third duct will be opened or closed as part of a variable cycle to transform it from a strike aircraft engine to a transport-type engine. If the duct is open the bypass ratio will increase, reducing fuel burn, and increasing subsonic range by up to 40 percent, leading to 60 percent longer loiter times on target. If the ducts are closed, additional air is forced through the core and high pressure compressor, enabling thrust and speed to increase and providing world-class supersonic performance.
GE's ADVENT designs are based on new manufacturing technologies like 3-D printing of intricate cooling components and super-strong but lightweight ceramic matrix composites. These allow the manufacture of highly efficient jet engines operating at temperatures above the melting point of steel.
Engineers also designed the new engine to be easy to fly. “We want the engine to take care of itself and let the pilot focus on the mission,” says Abe Levatter, project manager at GE Aviation. “When the pilot says ‘I’m out of danger, I want to cruise home,’ the engine reconfigures itself. We take it upon ourselves to make the engine optimized for whatever the pilot wants.”
GE is now testing the engine’s core components and plans to run a full test in the middle of 2013. The video below provides additional visual description of its operation.
