A recent collaboration between SpaceX and NASA made international headlines for marking the beginning of an era of commercial, manned space flights. However, a future of commercial space flights requires an increased efficiency of current rocket engines.
A typical rocket needs tremendous amounts of fuel just to get in orbit. In fact, the weight of fuel on NASA’s Space Shuttle was 20 times more than that of the body of the vehicle itself. Thus, costs can be significantly reduced by using more fuel-efficient engines.
Current combustion engines generate thrust by burning compressed fuel which releases energy in the form of expanding gas. However, a novel type of engine, the rotating detonation engine (RDE), employs a series of detonations to generate thrust. Because detonations are inherently unstable, a rotating detonation engine is designed to confine the series of detonations to the gap between concentric cylinders.
“Imagine you're driving on a crazy foggy road/racetrack,” James Koch, an alum from the department of mathematics, said. “All of a sudden, there is a car in front of you and you cannot brake or swerve in time to avoid it. So, you hit it. This is the shock wave. But now imagine the car's gas tank blows up on impact. The force of the explosion actually pushes your car further into the fog and you hit another car, and then there's another explosion and the process repeats.”
Even though detonation engines have the potential to be more efficient and cost effective, current designs are not stable enough due to the violent nature of detonations. While the rotating detonation engines are designed to make the process more stable, the detonations are still mostly unpredictable.
However, researchers at the UW recently developed a mathematical model describing the behaviour of such engines. To study the engines, the team first developed an experimental engine in the laboratory and collected data from over 1,000 experiments.
“We got really interesting data that showed the formation of the detonation waves and how they behave and interact with one another,” Koch said.
The team then developed mathematical models to replicate the observed behavior. They realized that the detonations were not completely random and did follow some structure.
“The theory we have developed provides the most (and only) comprehensive characterization of the RDE instabilities,” J. Nathan Kutz, an adjunct professor of applied mathematics, said.
The team developed an integrated theory that was simple and comprehensive, unlike other competing theories that only provided explanations for a single phenomenon.
“By bringing in the right physics, specifically the energy balance of energy across the entire cavity as well as at a combustion front, we were able to produce a simple model (by combustion standards) that produced all the effects observed in the experiment,” Kutz said. “This rarely happens, but in this case, it completely transformed the modeling space for RDEs.”
The team continues to build extra features in the model to account for the counter-propagating combustion waves while also working to establish a universality to the model for multiscale physics systems.
Reach reporter Akanksha Mishra at firstname.lastname@example.org. Twitter: @Akanksha_2200
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