A research team at the University of Central Florida (UCF) in the US has experimentally demonstrated a rocket propulsion system that was previously thought to be impractical. The system is known as the rotating detonation rocket engine. This technology is suitable for upper-stage rockets operating in space. Such engines would be lighter, more efficient and provide longer range than current upper stage rocket motors.

The research team’s results were published in the latest (April) edition of the journal Combustion and Flame. “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,” highlighted UCF Department of Mechanical and Aerospace Engineering Assistant Professor and research team leader Kareem Ahmed.

In a rotating detonation rocket engine, propulsion is provided by a continuous series of explosions that rotate around the inside of the engine. These explosions are fed by the injection of just the right amounts of oxygen and hydrogen. The concept has been under consideration since the 1960s but had previously proved impossible to realise in practice.

The explosions release energy bursts that travel at speeds between 7 200 km/h and 9 000 km/h, or more than five times the speed of sound (also phrased as being more than Mach 5, Mach 1 being the speed of sound). The engine is of durable construction, its body being manufactured from copper and brass. The release of the propellants into the engine has to be carefully balanced.

“We have to tune the sizes of the jets releasing the propellants to enhance the mixing for a local hydrogen-oxygen mixture,” he explained. “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.”

Of course, the team had to establish the success of their endeavours. This they did by injecting a tracer into the hydrogen fuel and using a high-speed camera to capture and quantify the detonation waves.

“You need the tracer to actually see that explosion that is happening inside and track its motion,” elucidated Ahmed. “Developing this method to characterise the detonation wave dynamics is another contribution of this article.”

“These research results already are having repercussions across the international research community,” reported (US) Air Force Research Laboratory Rotating Detonation Rocket Engine Programme lead researcher and study co-author William Hargus. “Several projects are now re-examining hydrogen detonation combustion within rotating detonation rocket engines because of these results. I am very proud to be associated with this high-quality research.”