New engine design fuels hopes of supersonic aviation revival

GE Aerospace, a leading jet engine producer, has announced the development of a functional rotating detonation engine (RDE), marking a departure from decades of experimental efforts.

America's Defense Advanced Research Projects Agency also granted a $29 million contract to Raytheon, a part of RTX, for the creation of an RDE named Gambit, The Economist reports.

These engines are designed to propel missiles, overcoming the limitations of current propulsion systems such as rockets and traditional jet engines. If successful, RDEs could play a broader role in aviation, potentially contributing to the revival of supersonic air travel.

In essence, an RDE "replaces fire with a controlled explosion," as explained by Kareem Ahmed, an aerospace engines expert at the University of Central Florida. Unlike conventional jet engines that rely on subsonic combustion (deflagration), RDEs utilise high-energy supersonic detonation, offering a more powerful and potentially efficient method of generating thrust.

While traditional jet engines involve complex systems with numerous moving parts, RDEs simplify the process. Incoming air is forced into a hollow space between concentric cylinders. When fuel is introduced, it mixes with oxygen and detonates, creating a rotating supersonic shock wave that sustains itself, eliminating the need for intricate components.

Ramjets and pulse jets, which also operate without compressors and turbines, exist but come with limitations. RDEs, being simple and compact, offer cost-effective and fuel-efficient solutions, enabling missiles to achieve speeds of up to five times the speed of sound (Mach 5).

Advancements in computer modelling, high-temperature-resistant alloys, and additive manufacturing (3D printing) have enabled the construction of RDEs. In 2020, Dr. Ahmed and his team developed an experimental rocket version for space missions, as reported by The Economist.

To power an aircraft, RDEs may require assistance during takeoff until sufficient air is forced into the engine for detonation to commence. The Lockheed SR-71 Blackbird, a high-altitude American spy plane, utilised a similar hybrid engine approach during the Cold War, reaching supersonic speeds by lighting up its afterburners.

While an RDE consumes less fuel than an afterburner, its potential noise output poses challenges for civilian use. This noise concern echoes the issues faced by Concorde, the world's only commercial supersonic airliner, leading to its expensive operations and route restrictions due to excessive noise. Boom, a Colorado-based firm, is working on a quieter and more economical supersonic aircraft called Overture, utilising conventional jets with specially designed intakes and exhaust nozzles.

Considering the noise factor, an RDE's integration into civilian aviation would require addressing sonic boom concerns. Researchers believe that by modifying aircraft fuselage and wings, the impact of the boom on the ground could be reduced. However, complete elimination seems unlikely, raising questions about whether future supersonic passenger planes would be confined to flying over oceans.

The transition of military technology to civilian aviation has historically taken time. Jet engines, initially appearing in the 1940s on fighter planes, only began replacing propeller-driven airliners in the late 1950s.

While RDEs show promise for revolutionising propulsion systems, passengers eager for faster transatlantic flights may have to wait a decade or more for practical implementation.