New Kind of Rocket Engine Test-fired at UAH

Mechanical and aerospace engineering master’s student Evan Unruh with his Rotating Detonation Engine at UAH’s Johnson Research Center. Photo by Michael Mercier / UAH

After a year of design and construction, a new kind of rocket engine has been test-fired at the University of Alabama in Huntsville.

Evan Unruh, a UAH mechanical and aerospace engineering master’s student, built the rotating detonation engine (RDE) through UAH’s Propulsion Research Center.

Initial funding for the project was provided by Gabe Xu, associate professor of mechanical and aerospace engineering and a PRC associate, through the National Science Foundation’s program Connecting the Plasma Universe to Plasma Technology in Alabama.

“Once I have finished the developmental testing of the engine, Dr. Xu and his student Michaela Spaulding will be using the engine for that program to research the effects of transient plasma ignition on the detonation reactions within the combustor,” Unruh said.

According to UAH, RDEs offer better fuel efficiency than continuous-burn solid or liquid propellant engines. “Instead of a continuous burn, RDEs use a continuous spinning explosion to create supersonic gas and generate thrust,” UAH said in a release.

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The RDE engine was first test-fired in August and has seen several test firings since.

“As a concept, RDEs may facilitate the design of more efficient rocket engines,” Unruh said. “This would enable rockets that could fly higher, faster and more efficiently, thereby enabling greater access to space than what we see today.”

RDEs are normally cylindrical, but Unruh’s design allows for additional things to be observed during a test-firing.

“By designing ours to have a racetrack shape, we are able to add optical windows in the straight sections that allow us to directly observe the detonation wave inside the combustor,” Unruh said. “In particular, this optical access will allow us to observe interactions between the detonation wave and the spray plumes of the propellants as they are injected into the engine.”

The detonation reaction in an RDE comes when a supersonic shock wave compresses a fuel and oxidizer mixture, UAH says.

“The reaction then occurs behind this high-pressure shock, and the expanding gases from the reaction in turn drive the shock wave forward, continuing the propagation of the detonation,” Unruh said. “This detonation reaction happens much faster than the deflagration-based reactions currently used in jet and rocket engine combustors.”

Though theory tells Unruh and others that detonation-based combustion should be more efficient than deflagration combustion, the next step is to put that theory to work practically.

“The next challenge is to further understand the detonation phenomenon so we can figure out how to finally build an engine that is more efficient than traditional deflagration-based engines,” Unruh said.

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