# Rotating detonation engine

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 more efficient than conventional deflagrative combustion by as much as 25%. Such an efficiency gain would provide major fuel savings.
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 detonations are 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

Several organizations work on RDEs.

### General Electric

In 2023 GE demonstrated a subscale laboratory turbine based combined cycle (TBCC) system that combined a Mach 2.5-class turbofan paired 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.

### 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 4,000 lbf (18 kN) of thrust. NASA has stated their intention to create a 10,000-pound-force (44 kN) 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 5,800-pound-force (26 kN) of thrust. Test stand video captured at NASA's Marshall Space Flight Center in Huntsville Alabama USA, 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 22,000 N (4,900 lbf) thrust rotating detonation rocket engine (RDRE) while testing with liquid oxygen and gaseous methane at Purdue University in 2021.

### 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 200 lbf (890 N) 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 class RDE in the second stage. The engine used gaseous methane and oxygen as propellants, generating an average thrust of 518 N 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 / N $_2$O propellant.

### Łukasiewicz Research Network - Institute of Aviation

On September 15, 2021, the Warsaw Institute of Aviation performed the first successful flight test of an experimental rocket powered by a rotating detonation rocket engine, powered by liquid propellants. The test took place on September 15, 2021, at the testing ground of the Military Institute of Armament Technology in Zielonka near Warsaw in Poland. The rocket engine, according to the plan, worked for 3.2 s, accelerating the rocket to a speed of about 90 m/s, which allowed the rocket to reach an altitude of 450 m.

### Beijing Power Machinery Institute

In 2023 researchers announced a demonstration unit of a hybrid air-breathing engine. It combines a continuous RDE for propulsion at below Mach 7 with an oblique detonation engine for use at speeds up to Mach 16. The oblique detonation waves are stationary and stabilized. BPMI is China's leading ramjet manufacturer.

### Chongqing University Industrial Technology Research Institute/Thrust-to-Weight Ratio Engine

Earlier in 2023, China achieved the world's first RDE drone flight. The drone successfully flew at an undisclosed airfield in Gansu province. The FB-1 Rotating Detonation Engine was developed jointly by Chongqing University Industrial Technology Research Institute and private company Thrust-to-Weight Ratio Engine (TWR).

### Other research

Other experiments have used numerical procedures to better understand the flow-field of the RDE. In 2020, a study from the University of Washington explored an experimental device that allowed control of parameters such as the width of the annulus. Using a high-speed camera, researchers were able to view it operating in extreme slow motion. Based on that they developed a mathematical model to describe the process.
In 2021, the Institute of Mechanics, Chinese Academy of Sciences, successfully tested the world's first hypersonic detonation wave engine powered by kerosene, which could propel a plane at Mach 9.