GE’s Ultimate Flying Machine

Building the Ultimate Flying Machine of GE

Jet engines come in an array of sizes and speeds, and as with many engineering projects, there is a balance between power and efficiency. Fighter jets use low-bypass turbofans to achieve fast bursts of speed, while commercial airliners use slower, more efficient high-bypass turbofans. GE Aviation engineers have taken this task to heart as they attempt to marry the best of both worlds.

GE Aviation has developed Adaptive Cycle Engine technologies that could precipitate fuel savings of up to 25 percent, which increases a military jet’s range by up to 35 percent. Playing off the ideas of Gerhard Neumann in the 1960s, the new technology allows an engine to switch between high power and high efficiency by adjusting the amount of air that flows through the engine core. With enhanced combat capability provided through increased thrust and significantly improved thermal management, the new technology also allows for unrestricted operation anywhere in the flight envelope.

A Whole New Engine

Switching between high efficiency and high power allows a turbine engine to continually optimize performance across the flight envelope. “[The system] varies the two propulsion parameters that impact thrust and specific fuel consumption: bypass ratio and fan pressure ratio,” says ADVENT (ADaptive Versatile ENgine Technology) project manager at GE Aviation, Dave Jeffcoat. “The adaptive cycle capability, combined with high pressure compressor improvements, advanced materials and cooling, and a third stream flow provide a generational leap in combat propulsion.”

The new engine has internal variable geometry features that allow the system to vary the bypass ratio and fan pressure ratio, optimizing engine operation for varying flight conditions. “By varying the fan pressure ratio and engine bypass ratio, a high thrust (high pressure ratio and low bypass ratio) state can be set for takeoff and acceleration. Similarly, for cruise, the engine can be set to operate at a low pressure ratio and high bypass ratio state, which minimizes fuel consumption,” Jeffcoat explains.

By combining an advanced compressor, advanced materials and cooling, and third stream architecture, the system offers an undeniable leap in aerospace propulsion technology. “The full double-digit levels of improvement that the adaptive cycle architecture provides is only possible by a completely new engine design/configuration optimized for the advanced capabilities,” he says. This new engine design has been heralded as the next generation in jet engines, but researchers claim that the technology is leaps and bounds ahead of previous models.

New Engine, New Materials

GE Aviation has integrated high temperature metal alloy and ceramic matrix composite materials, as well as advanced cooling technologies, into the ADVENT engine. Advanced aerodynamics and engine compression technologies coupled with reduced cooling airflow and high temperature metal and ceramic alloys are necessary to help deliver the levels of fuel efficiency to reduce the cost burden to the U.S. military driven by high fuel prices.

“The material technologies are a great opportunity to leverage billions of dollars in investment and millions of hours of proven experience from commercial engine programs,” Jeffcoat explains. “In addition to new materials, the industry is also taking advantage of new manufacturing methods like additive manufacturing and advanced casting processes that allow for incorporation of intricate cooling circuitry within turbine airfoils for improved cooling effectiveness.”

Further Testing

GE and Pratt & Whitney have found themselves taking different approaches to the military’s research in adaptive engine technologies. While the basic architecture, which includes an adaptive fan, cooled cooling air, and third stream, is similar between the two organizations, design implementation is where things differ. “The Adaptive Engine Technology Development (AETD) program is intended to assess the performance capability and risk through the Preliminary Design Review phase of the program,” Jeffcoat says.

The focus of the AETD adaptive engine architectures is on the compression systems. According to Jeffcoat, the effort includes the demonstration of an integrated augmentor-nozzle, third stream engine solution, which builds upon the ADVENT and other related research efforts that were focused on the turbomachinery. Rig and engine testing will be conducted as part of the AETD program as well, to demonstrate the aerodynamics of the newly integrated systems.

“Advanced afterburner (augmentor-nozzle) technology development is not part of these adaptive cycle technology demonstrator programs,” he explains. “However, the Propulsion System Contractors do have advanced technology augmentor and nozzle efforts underway that could be brought to bear once a decision is made to move forward with developing and fielding an advanced adaptive cycle propulsion system.”

The benefits afforded by the advanced materials, aerodynamics, and adaptive cycle are useable in a wide range of applications. “The magnitudes of the benefits are application specific with fighters showing the largest payoff due to the extensive range in operating conditions across their subsonic/supersonic flight envelope,” Jeffcoat says.

The next jet engine is well on its way, as the preliminary design review is set to be finished by the end of 2014, and rig and core testing is planned for 2015-16. A recent full-engine demonstration marks the end of GE’s ADVENT program, but manufacture and test activities for the follow-on AETD program have only just begun. GE Aviation has invested more than $1 billion in its adaptive cycle design, which integrates $600 million of proven commercial engine technologies, and looks to benefit both the military and commercial aerospace markets in years to come.