A rotating detonation engine (RDE) uses a form of pressure gain combustion, where one or more detonations continuously travel around an annular channel. Computational simulations and experimental results have shown that the RDE has potential in transport and other applications. In detonative combustion, the flame front expands at supersonic speed. It is theoretically up to 25% more efficient than conventional deflagrative combustion, potentially enabling increased fuel efficiency. Disadvantages include instability and noise.
Concept
The basic concept of an RDE is a detonation wave that travels around a circular channel (annulus). Fuel and oxidizer are injected into the channel, normally through small holes or slits. A detonation is initiated in the fuel/oxidizer mixture by some form of igniter. After the engine is started, the detonation is self-sustaining. One detonation ignites the fuel/oxidizer mixture, which releases the energy necessary to sustain the detonation. The combustion products expand out of the channel and are pushed out of the channel by the incoming fuel and oxidizer. Although the RDE's design is similar to the pulse detonation engine (PDE), the RDE can function continuously because the waves cycle around the chamber, while the PDE requires the chambers to be purged after each pulse.
Development The concept of rotating detonations emerged from theoretical studies on detonation waves and rocket engine combustion instability. Experimental observation and analysis first occurred in 1950s in both the Soviet Union and United States, followed by a prolonged period of limited research during the 1960s–1990s. In the Soviet Union, B. V. Voitsekhovskii pioneered the development, while in the United States, J.A. Nicholls at the University of Michigan advanced the concept through his investigations of detonations and tangential combustion instabilities in liquid rocket engines.
GE Aerospace In 2023 GE Aerospace demonstrated a subscale laboratory turbine-based combined-cycle (TBCC) system that combined a Mach 2.5-class turbofan with a rotating detonation-dual-mode ramjet (RD-DMRJ). The test came 18 months after program launch. The company reported rotating detonations of a compressed fuel-air mixture in the presence of the supersonic airflow necessary for speeds above Mach 5. In 2026, the company and Lockheed Martin announced a joint effort to produce a hypersonic missile powered by an RDE. The RDE is to initially accelerate the missile to supersonic speeds, at which point it will reconfigure to act as a ramjet, then reconfiguring to a scramjet to reach hypersonic speeds.
DARPA DARPA is working with RTX on Gambit, researching the application of rotating detonation engines for supersonic air-launched standoff missiles. DARPA is also working with Venus Aerospace which successfully tested its RDRE engine in March 2024.
US Navy The US Navy has been pushing development. Researchers at the Naval Research Laboratory (NRL) have a particular interest in the capability of detonation engines such as the RDE to reduce the fuel consumption of their ships. Several obstacles must still be overcome in order to use the RDE in the field. As of 2012, NRL researchers were focusing on better understanding how the RDE works.
Aerojet Rocketdyne Since 2010, Aerojet Rocketdyne has conducted over 520 tests of multiple configurations.
NASA Daniel Paxson at the Glenn Research Center used simulations in computational fluid dynamics (CFD) to assess the RDE's detonation frame of reference and compare performance with the PDE. He found that an RDE can perform at least on the same level as a PDE. Furthermore, he found that RDE performance can be directly compared to the PDE as their performance was essentially the same. On January 25, 2023, NASA reported successfully testing its first full-scale rotating detonation rocket engine (RDRE). This engine produced 18 kN (4,000 lbf) of thrust. NASA has stated their intention to create a 44 kN (10,000 lbf) thrust unit as the next research step. On December 20, 2023, a full-scale Rotating Detonation Rocket Engine combustor was reportedly fired for 251 seconds, achieving more than 26 kN (5,800 lbf) of thrust. Test stand video captured at NASA's Marshall Space Flight Center in Huntsville, Alabama, US, demonstrated ignition.
Energomash According to Russian Vice Prime Minister Dmitry Rogozin, in mid-January 2018 NPO Energomash company completed the initial test phase of a 2-ton class liquid propellant RDE and plans to develop larger models for use in space launch vehicles.
Purdue University In May 2016, a team of researchers affiliated with the US Air Force developed a rotating detonation rocket engine operating with liquid oxygen and natural gas as propellants. Additional RDE testing was conducted at Purdue University, including a test article called "Detonation Rig for Optical, Non-intrusive Experimental measurements (DRONE)", an "unwrapped" semi-bounded, linear detonation channel experiment. IN Space LLC, in a contract with the US Air Force, tested a 4,900 lbf (22 kN) thrust rotating detonation rocket engine (RDRE) while testing with liquid oxygen and gaseous methane at Purdue University in 2021.
D-propulse India-based defence start-up D-Propulse announced the successful demonstration of a 5 kN-class rotating detonation engine (RDE) at a Defence Research and Development Organisation facility in Hyderabad.
University of Central Florida In May 2020, a team of engineering researchers affiliated with the US Air Force claimed to have developed a highly experimental working model rotating detonation engine capable of producing 890 N (200 lbf) of thrust operating on a hydrogen/oxygen fuel mix. In 2021 the group demonstrated an oblique detonation wave engine with a ramp angle of 30 degrees.
JAXA On July 26, 2021 (UTC), Japan Aerospace Exploration Agency (JAXA) succeeded in testing the RDE in space for the first time in the world by launching the S-520-31 sounding rocket equipped with a 500 N (110 lbf) class RDE in the second stage. The engine used gaseous methane and oxygen as propellants, generating an average thrust of 518 N (116 lbf) and delivering 290 seconds of specific impulse. Rotating combustion also created a torque of 0.26 N·m, so a S-shaped pulse detonation engine was used to reduce the spin of the stage. S-520-34 launched on November 14, 2024, experimented successfully with a liquid ethanol / N2O propellant.
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