Li Qiao, a professor in Purdue University’s College of Engineering, is testing a Tesla valve-inspired design to improve the performance of rotating detonation engines. (Image: Purdue University)

Researchers in Purdue University’s College of Engineering are testing a patented Tesla valve-inspired injection manifold design that could improve the performance of rotating detonation engines (RDEs). RDEs are being developed as next-generation solutions in the field of jet and rocket propulsion.

Professor Li Qiao is conducting numerical demonstrations on the design.

Qiao said RDEs convert chemical energy into thrust, with a flame traveling through the engine at supersonic speed, which can be 10 times faster than in a traditional engine.

Qiao said RDEs face stability drawbacks, however. The pressure behind a detonation wave in the engine is enormous, but there is high pressure on the wave to move backward. That pressure could reverse the flow of the fuel and oxidizer injectors.

“If the injection flow goes backward, the engine can lose power and power generation is lost,” Qiao said. “The pressure may cause oscillation, too, which causes damage to the fuel injection system.”

Qiao said Purdue’s Tesla valve-designed injection manifold sustains a stable shock wave in RDEs, maintaining detonation and thrust while preventing the reverse flow.

“Tesla valves allow fluids to flow in one direction but make it virtually impossible for them to travel in another,” Qiao said. “Tesla valves are already frequently used in other fluid devices, but ours is the first proposal to use them as injection manifolds in RDEs.”

During numerical demonstrations on the injection manifold design, Qiao discovered in traditional designs that a significant amount of flow made its way back to the inlet where the fuel was injected.

“In tests of the Tesla valve-inspired injection manifold design, very little flow returned to the inlet,” Qiao said. “The majority of flow was self-impinged at the corresponding Tesla valves.”

Qiao and her team are looking to further perfect the design, which can be integrated into existing engine systems.

“We would be happy to work with industry and the federal government to apply this valve concept for specific engines in commercial and defense applications,” Qiao said.

Qiao has disclosed the innovation to the Purdue Innovates Office of Technology Commercialization, which applied for and received a patent on the intellectual property from the U.S. Patent and Trademark Office.

Here is an exclusive Tech Briefs interview — edited for length and clarity — with Qiao.

Tech Briefs: I'm sure there were too many to count, but what was the biggest technical challenge you faced while developing this valve design?

Qiao: First, let me talk about the whole RDE background. This is a technology that's becoming very hot. It's like all the propulsion, space, energy sectors are looking into this technology because it can potentially increase efficiency, reduce fuel consumption, and increase performance. A lot of defense energy companies are investing in this technology, particularly for the space industry because research has shown RDE may be most promising for space applications.

So, getting back to your question, there are several obstacles. The biggest challenge, I would say, for RDE technology development, is that because of the strong, high-pressure wave behind the shocks, due to the detonation, you change, push the flow backwards. Basically, trying to feed the combustor with fuel and oxidizer flows, but now you have a strong wind.

Now what happens if you’re flying on a jet engine? Suddenly, for some reason, you cut off fuel supply; you're going to lose power, you're going to lose thrust immediately. So, that's the challenge. How to provide stable fuel and oxidizer flow . The oxidizer is for rocket applications; you need to carry both on board. So, how to provide a constant flow into the combustor despite the high pressure resulting from the detonation. That's the key.

We have a unique design of the fuel and oxidizer manifold that basically says, ‘OK, flow is only going in this direction, but not backwards even though your back pressure is higher.’ That prevents the flow from reversing.

Tech Briefs: You’re quoted as saying, ‘We would be happy to work with industry and federal government to apply this valve concept for specific engines and commercial defense applications.’ My question is, how is that coming along? Do you have any updates you can share or any new developments?

Qiao: We have done some numerical simulations that demonstrate the potential of the design. But, we do not have the funding to do the testing. So, if industry is interested, they can invest to improve the design based on our foundational ideas — and also to customize it for their own particular application. Because every time you work on rockets or gas turbine or any energy devices, basically it’s a different machine, so it needs to be customized to adapt to the flow rate they're looking as, well as other details.

Tech Briefs: What are your next steps? Do you have any plans for further research work or anything else?

Qiao: At university, basically we're looking for funding to further refine this technology. But I would be happy to see it being tried on actual engines — that’s our bottleneck right now, but we can solve it. The problem is that we, as a university, don't work on those big things. So, for example, I can't have a rocket in my lab.

Tech Briefs: Do you have any advice for engineers aiming to bring their ideas to fruition?

Qiao: I always encourage our students to think about finding patterns in their research, because we do not have a strong culture that encourages the students to look for patterns in the lab.

In terms of working professionals, like engineers who are already in the industry, I would say working with universities could help them develop their products (and their careers) — basically, working together, we can make things work.