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Pratt & Whitney is planning further development of rotating detonation engine (RDE) technology following “positive test results” from a series of ground tests.
The work, which was completed with the RTX Technology Research Center, marks another step forward for this novel propulsion concept, which offers high thermal efficiency and performance in a relatively compact form factor. The technology is under study for potential applications in high-speed air-breathing missiles and aircraft.
“Positive test results are spurring additional internal investment as Pratt & Whitney works with the Department of Defense to accelerate a path to an integrated engine and vehicle ground test in the coming years,” the company says. “Our testing simulated aggressive assumptions for how and where the rotating detonation engine needs to perform,” adds Chris Hugill, senior director of Pratt & Whitney’s rapid prototyping arm Gatorworks.
In an RDE, combustion occurs in the form of a detonation wave that travels around an annulus in a gap between coaxial cylinders. The detonation wave combusts the fuel-air mixture at supersonic speeds and at near-constant volume—a more efficient process than current jet engines in which combustion occurs as a subsonic deflagration under constant pressure.
Because the heat-release process is more compact in an RDE and occurs over a shorter distance, the overall propulsion system can be smaller. This has the potential to reduce the overall weight of the engine as well as shortening the length of a combustion module in a dual-mode ramjet (DMRJ) or turbine-based combined cycle (TBCC). This feature could make it possible to design a hypersonic cruise missile short enough for use by a carrier-based fighter or could reduce the length of a TBCC in a reusable hypersonic vehicle by about one-third.
Pratt confirms the tests were completed under a U.S. Air Force Research Laboratory contract announced in March 2022, and were run jointly with parent company partners RTX Missiles & Defense as well as the RTX Technologies Research Center. The engine-maker declines to specify whether the proposed follow-on integrated engine and vehicle test will be conducted under an Air Force or U.S. Navy effort, saying only, “We are in conversation with multiple Department of Defense entities.”
Pratt & Whitney does, however, confirm the RDE test results are encouraging enough for it to consider integrating it into the company’s Metacomet, an advanced propulsion study concept launched in 2018 to focus on low-cost alternatives to ramjet and scramjet propulsion for high-speed flight. The Metacomet design builds on experience with the J58 turbojet developed for the Mach 3+ Lockheed SR-71 and does not require the addition of a pure ramjet/scramjet cycle or the complexities of mode transition to and from turbine power.
“We cannot say much about Metacomet right now, but at [Pratt & Whitney], RDE is just one of a portfolio of technologies that show promise for future applications. Advanced engine concepts such as Metacomet, which weren’t first envisioned to take advantage of RDE technology, perhaps could, and we’re looking at that,” the engine manufacturer says.
Interest in developing compact, efficient and powerful combustion systems for advanced high-speed propulsion also extends beyond missile applications to reusable high-speed vehicles such as DARPA’s Next-Generation Responsive Strike (NextRS) system. The research agency released solicitations for industry feedback on the NextRS concept in April 2024 and has outlined a TBCC-powered concept that would be ready to fly by the end of the decade.
GE Aerospace is also researching high-speed propulsion systems incorporating RDEs and is conducting follow-on tests of a DMRJ after initial runs began at the company’s Evendale, Ohio, facility in March 2024. Houston-based Venus Aerospace, meanwhile, is developing a rocket-based combined-cycle propulsion system that combines a rotating detonation rocket engine with a ramjet.
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