Researchers from the University of Central Florida and the US Naval Research Laboratory have discovered an experimental configuration and flow conditions that generate a stabilized oblique detonation—a phenomenon that has the potential to revolutionize high-speed propulsion of the future. An open-access paper on their work is published in Proceedings of the National Academy of Sciences (PNAS).

Future terrestrial and interplanetary travel will require high-speed flight and reentry in planetary atmospheres by way of robust, controllable means. This, in large part, hinges on having reliable propulsion systems for hypersonic and supersonic flight. Given the availability of fuels as propellants, we likely will rely on some form of chemical or nuclear propulsion, which means using various forms of exothermic reactions and therefore combustion waves. Such waves may be deflagrations, which are subsonic reaction waves, or detonations, which are ultrahigh-speed supersonic reaction waves. Detonations are an extremely efficient, highly energetic mode of reaction generally associated with intense blast explosions and supernovas.

Detonation-based propulsion systems are now of considerable interest because of their potential use for greater propulsion power compared to deflagration-based systems. An understanding of the ignition, propagation, and stability of detonation waves is critical to harnessing their propulsive potential and depends on our ability to study them in a laboratory setting.

Here we present a unique experimental configuration, a hypersonic high-enthalpy reaction facility that produces a detonation that is fixed in space, which is crucial for controlling and harnessing the reaction power. A standing oblique detonation wave, stabilized on a ramp, is created in a hypersonic flow of hydrogen and air. Flow diagnostics, such as high-speed shadowgraph and chemiluminescence imaging, show detonation initiation and stabilization and are corroborated through comparison to simulations. This breakthrough in experimental analysis allows for a possible pathway to develop and integrate ultra-high-speed detonation technology enabling hypersonic propulsion and advanced power systems.

—Rosato et al.

Schematic of oblique detonation engine concept. The experimental and computational ODW domains are highlighted along with their location in the engine flow path. Rosato et al.

The system could allow for air travel at speeds of Mach 6 to 17—more than 4,600 to 13,000 miles per hour. The technology harnesses the power of an oblique detonation wave, which they formed by using an angled ramp inside the reaction chamber to create a detonation-inducing shock wave for propulsion.

Unlike rotating detonation waves that spin, oblique detonation waves are stationary and stabilized.

The technology improves jet propulsion engine efficiency so that more power is generated while using less fuel than traditional propulsion engines, thus lightening the fuel load and reducing costs and emissions.

In addition to faster air travel, the technology could also be used in rockets for space missions to make them lighter by requiring less fuel, travel farther and burn more cleanly.

Detonation propulsion systems have been studied for more than half a century but had not been successful due to the chemical propellants used or the ways they were mixed. Previous work by study co-author Kareem Ahmed’s group in UCF’s Department of Mechanical and Aerospace Engineering overcame this problem by carefully balancing the rate of the propellants hydrogen and oxygen released into the engine to create the first experimental evidence of a rotating detonation.

However, the short duration of the detonation, often occurring for only micro or milliseconds, makes them difficult to study and impractical for use.

In the new study, however, the UCF researchers were able to sustain the duration of a detonation wave for three seconds by creating a new hypersonic reaction chamber, known as a hypersonic high-enthalpy reaction, or HyperREACT, facility. The facility contains a chamber with a 30-degree angle ramp near the propellent mixing chamber that stabilizes the oblique detonation wave.

This is the first time a detonation has been shown to be stabilized experimentally. We are finally able to hold the detonation in space in oblique detonation form. It’s almost like freezing an intense explosion in physical space.

—Kareem Ahmed

Gabriel Goodwin, an aerospace engineer with the Naval Research Laboratory’s Naval Center for Space Technology and study co-author, says their research is helping to answer many of the fundamental questions that surround oblique detonation wave engines.

Goodwin’s role in the study was to use the Naval Research Laboratory’s computational fluid dynamics codes to simulate the experiments performed by Ahmed’s group.

Lead author is Daniel Rosato, now a graduate research assistant and a recipient of UCF’s Presidential Doctoral Fellowship, has been working on the project since he was an aerospace engineering undergraduate student and is responsible for experiment design, fabrication, and operation, as well as data analysis, with assistance from Mason Thorton, a study co-author and an undergraduate research assistant.

Rosato says the next steps for the research are the addition of new diagnostics and measurement tools to gain a deeper understanding of the phenomena they are studying.

After that, we will continue exploring more experimental configurations to determine in more detail the criteria with which an oblique detonation wave can be stabilized.

—Daniel Rosato

If successful in advancing this technology, detonation-based hypersonic propulsion could be implemented into human atmospheric and space travel in the coming decades, the researchers say.

The study was funded by the long-term support of the Energy, Combustion and Non-Equilibrium Thermodynamics Portfolio of the Air Force Office of Scientific Research in the area of detonation via grants 16RT0673/FA9550-16-1-0441 and 19RT0258/FA9550-19-0322 (Program Manager: Chiping Li), the National Science Foundation and the NASA Florida Space Grant Consortium.

Resources

• Daniel A. Rosato, Mason Thornton, Jonathan Sosa, Christian Bachman, Gabriel B. Goodwin, Kareem A. Ahmed (2021) “Stabilized detonation for hypersonic propulsion” Proceedings of the National Academy of Sciences 118 (20) e2102244118; doi: 10.1073/pnas.2102244118