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GE Aerospace says it successfully demonstrated an advanced jet propulsion concept that involves a dual-mode ramjet design utilizing rotating detonation combustion. This could offer a pathway to the development of new aircraft and missiles capable of flying efficiently at high supersonic and even hypersonic speeds across long distances.

A press release that GE Aerospace put out today offers new details about what it says “is believed to be a world-first hypersonic dual-mode ramjet (DMRJ) rig test with rotating detonation combustion (RDC) in a supersonic flow stream.” Hypersonic speed is defined as anything above Mach 5. Amy Gowder, President and CEO of the Defense & Systems division of GE Aerospace, previously disclosed this project, but offered more limited information, at this year’s Paris Air Show in June.

“A typical air-breathing DMRJ propulsion system can only begin operating when the vehicle achieves supersonic speeds of greater than Mach 3,” the press release explains. “GE Aerospace engineers are working on a rotating detonation-enabled dual mode ramjet that is capable of operating at lower Mach numbers, enabling the flight vehicle to operate more efficiently and achieve longer range.” 

“RDC [rotating detonation combustion] enables higher thrust generation more efficiently, at an overall smaller engine size and weight, by combusting the fuel through detonation waves instead of a standard combustion system that powers traditional jet engines today,” the press release adds.

To elaborate, in most traditional gas turbines, including turbofan and turbojet engines, air is fed in from an inlet and compressed, and then is mixed with fuel and burned via deflagration (where combustion occurs at a subsonic rate) in a combustion chamber. This process creates the continuous flow of hot, high-pressure air needed to make the whole system run.

A rotating detonation engine (which involves combustion that happens at a supersonic rate) instead “starts with one cylinder inside another larger one, with a gap between them and some small holes or slits through which a detonation fuel mix can be pushed,” according to a past article on the general concept from New Atlas. “Some form of ignition creates a detonation in that annular gap, which creates gases that are pushed out one end of the ring-shaped channel to produce thrust in the opposite direction. It also creates a shockwave that propagates around the channel at around five times the speed of sound, and that shockwave can be used to ignite more detonations in a self-sustaining, rotating pattern if fuel is added in the right spots at the right times.”

Experimentation with rotating detonation concepts dates back to the 1950s, but actually creating a workable engine of this type had proved elusive until very recently, at least publicly. In 2020, a team at the University of Central Florida (UCF), working together with the U.S. Air Force’s Air Force Research Laboratory (AFRL), said they had created a first-of-its-kind experimental test rig that demonstrated the concept’s practical feasibility. The following year, the researchers at UCF announced they had built a prototype engine capable of producing a sustained detonation wave, said to be another world’s first. There have been additional developments with regard to rotating detonation engines elsewhere in the United States and around the world since then.
In principle, rotating detonation requires less fuel to produce the same level of power/thrust as combustion via deflagration. The resulting sustained shockwave builds its own pressure, as well, leading to even greater fuel efficiency. Pressure is steadily lost during deflagration.