New solid fuel developed by Purdue researchers set to improve stability, efficiency of rotating detonation engines

WEST LAFAYETTE, Ind. — Purdue researchers are developing a safer, more energy dense fuel for rotating detonation engines (RDE), a new type of jet engine used in military and space applications that is designed to be more powerful and efficient than traditional versions.

Steven Son, the Alfred J. McAllister Professor of Mechanical Engineering, and Terrence Meyer, professor of mechanical engineering, are collaborating with the Air Force Research Laboratory (AFRL) and Spectral Energies to build formulations for solid fuels that will power an RDE.

“The idea to use solid propellants for rotating detonation is a fairly new one, so some of the innovative work happening at Purdue is really cutting-edge technology,” said Eric Paulson, AFRL senior aerospace engineer and a lead collaborator on this project. “There’s a lot of work that’s been done with liquids, but solid fuel in an RDE is a pretty new game. It’s a very high interest technology across the Department of Defense.”

Son and Meyer’s team, funded by the AFRL Regional Network – Midwest, is identifying the types of solid fuels that decompose on their own and produce gases that are highly detonable and can be integrated into the RDE architecture. The goal is to transition this new technology to the defense market. The AFRL Regional Network – Midwest cultivates strategic collaborations in support of the AFRL to drive innovative research, translation and workforce development opportunities that bolster the critical technology needs of the U.S. Air Force. 

“I think the philosophy of the AFRL Midwest Network recognizes the Air Force benefits from the strong commitment and local investments made by Midwestern states and local governments in developing an environment that supports R&D, workforce development and the regional industrial base,” said Eric Lam, collaboration director for the AFRL Regional Network – Midwest. “The network is excited to enable this collaboration between Purdue and the AFRL Aerospace Systems Directorate to innovate propulsion technology. It is another demonstration of how the Air Force’s relationship with our academic ecosystem is key to our country’s technological advantage in defense applications.”

Solid fuels were chosen because of their stability and efficiency. They are less temperamental than liquid or gas fuels, have a longer shelf life and provide greater energy density, meaning less fuel is required to power the vehicle.

“Safety is one of the biggest reasons why we’re working with solid fuels,” Son said. “If you get a hole in a liquid fuel tank, then you’re going to have a leak that could cause a fire hazard. Solid fuels don’t have that problem.”

RDEs and solid fuels have the potential to advance rocket propulsion and hypersonic flight. Unlike traditional propulsion engines that use subsonic combustion to power up, RDEs operate through supersonic detonation, which burns fuel more efficiently and requires lighter and simpler components. Adding a solid fuel into the equation further enhances the vehicle’s fuel economy.

“The detonation wave in an RDE propagates at over 3,000 mph, which is about 100 times faster than a typical engine,” Meyer said. “This increase in power means that the combustor can be made more compact and lightweight and achieve more thrust with less fuel.

Because this research delves into relatively uncharted territory, there are several challenges that the group is working through. RDEs are typically designed for liquid and gas fuels, so solid fuels must be tailored to fit with the engine’s structure.

“The challenges come from trying to integrate several different systems together. We have to develop and characterize our solid fuel and tailor it to a very specific application,” said Eric Holst, a Purdue graduate research assistant on the project who is pursuing his PhD in aeronautics and astronautics. “Not that many people who are familiar with RDEs also have expertise in solid fuels and vice versa. So, it’s kind of unique bringing these two different research areas into one complete package.”

So far, the team has identified several candidate fuels it hopes to begin testing in an RDE currently housed in Maurice J. Zucrow Laboratories. The team has used a variety of imaging tools to measure the concentration of gases produced by the solid fuel exhaust and determine how fast those products are able to detonate.

“We’ve demonstrated burning propellants and producing something that can then burn again in an RDE,” Paulson said. “That proof of concept is key to being able to generate additional funds that mature this technology for an actual defense application.”

Son and Meyer, in partnership with Spectral Energies, will use additional funding from the AFWERX Small Business Technology Transfer program to scale up production of the solid fuel and begin integrating the solid fuel into an RDE. They will include additional additives in the fuel formulation to produce exhaust products that are more tailored to the engine and update the experimental setup to ensure the exhaust is measured in a more realistic environment.

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Media contact: Lindsey Macdonald, macdonl@purdue.edu