In this series discussing the International Air Transport Association (IATA) Technology Roadmap, we discussed New Engine Architectures and Advanced Engine Concepts. This web story will cover the Engine Cycle and two companies supporting those developments.
Two engine cycle ideas are presented by the IATA Technology Road Map dealing with improvements to the Gas Turbine Engine Cycle, which currently powers large aircraft.
The first of these concepts is the Adaptive/Active Flow control engine cycle which will be discussed in this webstory. We will cover the second topic – Ubiquitous Composites in a later story.
Figure 1: Airflow visualization in and Adaptive/Active Flow Control Engine
The Adaptive/Active Flow control engine concept is different from other engine cycles because aircraft jet engines are currently designed to operate optimally for a traditional single point. For instance, fighter aircraft engines are designed for high speed, while commercial jet engines are designed for high fuel efficiency. As a result fighter engines and commercial jets use radically different engines. The Adaptive Engine would however be designed to operate under both those conditions.
This idea, as initially presented, had a very low technology readiness (TRL) level of 2! NASA considers this stage to be one where the application is being formulated. Despite this low TRL level, the Entry in Service (EIS) was estimated at that time to be post-2020. But the IATA Technology Road Map has very little to say on this topic which requires some further research.
Pratt and Whitney XA101
One of the first institutions to experiment with new aircraft and engine concepts is the military. In this case, Pratt & Whitney and General Electric Aviation received substantial contracts of $1 billion each in 2012 to develop the Adaptive Engine Transition Program or AETP. The AETP was a five-year program that has now evolved to the next stage.
The Pratt and Whitney XA101 demonstrator program was designed for the Lockheed Martin F-35 Lightning II and was to form the United States Air Force’s sixth-generation fighter program. The 45,000 lbf (200 kN) thrust class engine is expected to be significantly more powerful and efficient than existing low-bypass turbofans. This three-stream adaptive cycle design can direct air to the bypass third stream for increased fuel efficiency and cooling or to the core and fan streams for additional thrust and performance. This is how Adaptive/Active Flow control takes place.
Figure 2: XA101 Adaptive Fan being tested at Arnold Engineering Development Complex (AEDC)
Specific goals for this program include reducing average fuel consumption by 25% and reducing the temperature of cooling air produced by the engine while it operates efficiently under mixed flight conditions, such as subsonic, transonic and supersonic. While this powerplant is still under development (as one can tell from Figure 2 and 3), the proponents believe that the XA101 was always intended to be a sixth-generation powerplant for sixth-generation fighters, such as the F-35.
The design of the XA101 has created a three-stream adaptive cycle engine that can adjust the bypass ratio and fan pressure to increase fuel efficiency or thrust, depending on the pilot’s/aircraft needs. A third bypass stream around the entire engine modulates a portion of airflow into the engine core to increase fuel economy and potentially act as a heat sink for cooling. Also, when additional thrust is needed, the air from the third stream can be directed into the core and fan streams for improved performance. The increased cooling and power generation also enable the potential employment of directed-energy weapons coming in the future.
General Electric XA100
The General Electric XA100 is the other AETD project which was financed to support the 6th generation fighter program.
Figure 3: The XA100 in test cell development at the Air Force’s Arnold Engineering Development Complex (AEDC)
The XA100 is also a three-stream adaptive cycle engine that can adjust the bypass ratio and fan pressure to increase fuel efficiency or thrust, depending on the scenario. It does this by employing an adaptive fan that can direct air into a third bypass stream to boost fuel economy and act as a heat sink for cooling; in particular, this would enable greater use of the high speed, low-altitude part of the F-35 envelope. The increased cooling and power generation also enable the potential employment of directed energy weapons in the future. When additional thrust is needed, the air from the third stream can be directed to the core and fan streams. In addition to the three-stream adaptive cycle configuration, the engine uses new heat-resistant materials such as ceramic matrix composites (CMC) to support higher turbine temperatures and improved performance. According to GE, the engine can offer up to a 35% increased range and a 25% reduction in fuel burn over current low-bypass turbofans.
Conclusion
In reviewing these engines, we see that two competitors are being supported to develop a novel engine cycle which obviously has opportunities in the 6th generation fighter and then later with further refinements in the aviation sector. So while EnviroTREC and its partners are focused on civilian (i.e. commercial gas turbine engines), these two projects involving the Adaptive/Active Flow control engine cycle are a prelude to what will coming our way at a future date.