Engineers Just Fired up an 'Impossible' Rotating Detonation Engine for the First Time

This groundbreaking new rocket-propulsion system can make space missions lighter and burn cleaner.
Derya Ozdemir

The impossible has just become possible: A team of researchers working with the US Air Force have just built and successfully tested an experimental model of a rotating detonation engine, which uses spinning explosions inside a circular channel to generate super-efficient thrust. 

This is incredibly important news since these types of engines require far less fuel than the regular internal combustion engines currently used to power rockets. This could be the future of getting our ships into space: a way that is more efficient and much lighter. 


Combustion vs. Detonation

Here is the thing: combustion is a relatively slow and controlled process and results from the reaction between fuel and oxygen at high temperatures. Engines which use combustion is a technology that we've known for a long time. 

However, pioneered by engineers in the 1950s, detonation is a rather new technology. It releases more energy from significantly less fuel mass than combustion, which is the reason why rocket scientists have been working on the idea of a rotating detonation rocket as a way to cut down weight and add thrust. It is fast, chaotic, and we are not that good at predicting it, which is the reason why it has been difficult to achieve and sustain. 

It works!

Now, a team of engineers from the University of Central Florida, working with the Rotating Detonation Rocket Engine Program at the Air Force Research Laboratory, seems to have got it figured. 

Their working laboratory model is a 3-inch copper test rig using a mix of hydrogen and oxygen for fuel.

Engineers Just Fired up an 'Impossible' Rotating Detonation Engine for the First Time
Source: Kareem Ahmed/University of Central Florida

Kareem Ahmad, an assistant professor in UCF's Department of Mechanical and Aerospace Engineering, says, "The study presents, for the first time, experimental evidence of a safe and functioning hydrogen and oxygen propellant detonation in a rotating detonation rocket engine. The detonation is sustained continuously until you cut off the fuel. We have tested up to 200 lbf, but the thrust increases linearly with the propellant mass flow."

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The secret was a tune-up

In order to achieve this revolutionary feat, the researchers needed a tune-up.

The team created a careful balance of the hydrogen and oxygen, which they tried out on their small, 3-inch rotating detonation rocket engine, remodeled after one designed by the US Air Force Research Laboratory.

According to Ahmed, "We have to tune the sizes of the jets releasing the propellants to enhance the mixing for a local hydrogen-oxygen mixture. So, when the rotating explosion comes by for this fresh mixture, it's still sustained. Because if you have your composition mixture slightly off, it will tend to deflagrate, or burn slowly instead of detonating."

It worked. In order to prove it, the team injected a methane tracer into the hydrogen and used a camera to capture the detonation waves. 

Engineers Just Fired up an 'Impossible' Rotating Detonation Engine for the First Time
Source: Sosa, Hargus/Combustion and Flame

According to the team, these images show continuous five-wave co-rotating detonations moving in a counter-clockwise direction.

You can watch this video of the rocket firing below.

Groundbreaking results created a wave among community

According to William Hargus, who is the lead of the Air Force Research Laboratory's Rotating Detonation Rocket Engine Program, the results have created a new wave among the international research community. "Several projects are now re-examining hydrogen detonation combustion within rotating detonation rocket engines because of these results."

This is such exciting news. The engine design is being evaluated as a possible replacement for Aerojet Rocketdyne's RL-10 rocket, according to New Atlas. "The U.S. Air Force is targeting a rocket launch flight test by 2025, and we are contributing to achieving that goal." says Ahmed.

Rotating detonation engines could lighten rocket payloads, reduce the costs of rocket launched, and moreover, could result in a 25% reduction in fuel use in US Navy ships.

The team has published the study in the journal Combustion and Flame.