Novel Engine Could Make Rockets Fuel Efficient, Lightweight: Study

Researchers have developed a computer model to describe how a new type of engine -- called a rotating detonation engine -- works, an advance they claim could make rockets more fuel-efficient, lightweight, and less complicated to construct. According to the study, published in the journal Physical Review E, this engine has been too unpredictable to be used in an actual rocket until now.

However, the scientists from the University of Washington (UW) in the US said the new model can allow engineers to develop tests to improve these engines and make them more stable. "The rotating detonation engine field is still in its infancy. We have tons of data about these engines, but we don't understand what is going on," said study lead author James Koch from UW.

"I tried to recast our results by looking at pattern formations instead of asking an engineering question -- such as how to get the highest performing engine -- and then boom, it turned out that it works," Koch said. While a conventional rocket engine works by burning propellant and then pushing it out of the back of the engine to create thrust, the researchers said a rotating detonation engine takes a different approach to how it combusts fuel.

"It's made of concentric cylinders. Propellant flows in the gap between the cylinders, and, after ignition, the rapid heat release forms a shock wave, a strong pulse of gas with significantly higher pressure and temperature that is moving faster than the speed of sound," Koch said. "This combustion process is literally a detonation -- an explosion -- but behind this initial start-up phase, we see a number of stable combustion pulses form that continue to consume available propellant," he added.

With this process, the scientists said high pressure and temperature are produced that drive exhaust out the back of the engine at high speeds, generating thrust. They said conventional engines use a lot of machinery to direct and control the combustion reaction so that it generates the work needed to propel the engine. But in a rotating detonation engine, the shock wave naturally does everything without needing additional help from engine parts, the study noted.

"The combustion-driven shocks naturally compress the flow as they travel around the combustion chamber. The downside of that is that these detonations have a mind of their own. Once you detonate something, it just goes," Koch said. To describe how these engines work, the researchers first developed an experimental rotating detonation engine where they could control different parameters, such as the size of the gap between the cylinders.

They also recorded the combustion processes with a high-speed camera at 240,000 frames per second to see what was happening in slow motion. The scientists then developed a mathematical model to mimic what they saw in the videos. "This is the only model in the literature currently capable of describing the diverse and complex dynamics of these rotating detonation engines that we observe in experiments," said study co-author J. Nathan Kutz, a UW professor of applied mathematics.

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Using the model, the researchers determined for the first time whether an engine of this type would be stable or unstable. "This new approach is different from conventional wisdom in the field, and its broad applications and new insights were a complete surprise to me," said study co-author Carl Knowlen, a UW research associate professor in aeronautics and astronautics.

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