Space

NASA's rotating detonation rocket engine posts record test results

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NASA has successfully tested a rotating detonation engine to more than 4,000 lb of thrust, in partnership with In Space LLC
NASA
NASA has successfully tested a rotating detonation engine to more than 4,000 lb of thrust, in partnership with In Space LLC
NASA
The engine was fired for a total of nearly 10 minutes, showing off its ability to withstand the extreme forces of sustained detonation
NASA

Explosions get you much more bang from your fuel buck than combustion – if your engine can withstand them. NASA believes the rotating detonation engine could be the future of deep space travel, and it's getting strong results in prototype testing.

Combustion engines are tried and true, and however angry they might look and sound in a top-fuel dragster or space rocket booster, the combustion process of oxidizing fuel in air is relatively slow and predictable. Detonation, on the other hand, is as chaotic and destructive as it sounds. It's how most bombs work; you take an explosive fuel and hit it with a jolt of energy, and the chemical bonds holding each molecule together break apart, releasing wild amounts of energy in a shockwave that expands at supersonic speed.

NASA, along with many other groups, wants to harness these explosions for a couple of key reasons. Firstly, detonation engines have a considerably higher theoretical level of efficiency than combustion engines, perhaps as much as 25%; they should be able to produce more thrust using less fuel and a smaller rocket. In the engineering and economics of space flight, that means cheaper launches, more billable payload, and greater distances.

They're also relevant to hypersonic flight. Combustion engines can only operate at subsonic airspeeds. To go supersonic or hypersonic, the intake air needs to be rapidly decelerated to a subsonic speed for combustion to take place. This generates heat and drag. Detonation occurs at supersonic speeds, so in addition to greater efficiency, you also reduce heat and drag in hypersonic applications since you don't need to slow the air down nearly as much.

Rotating detonation engines (RDEs), as opposed to oblique wave detonation engines or pulse detonation engines, use ring-shaped chambers and precisely-timed fuel injection to generate constant thrust. Each explosion sends out a shockwave that produces thrust, but it also travels around the ring to trigger the next explosion.

A number of groups are now reporting successful test firing of rotating detonation engines, from the University of Central Florida, working with the Air Force Research Laboratory, to Australia's RMIT, working with DefendTex, to Houston company Venus Aerospace, Aerojet Rocketdyne, and others... Jaxa, the Japanese space agency, has even gone so far as to test a small one in space.

The engine was fired for a total of nearly 10 minutes, showing off its ability to withstand the extreme forces of sustained detonation
NASA

NASA is keeping its testing on terra firma for the time being, but it's now announced the successful testing of a small RDE last year, in partnership with Indiana company In Space LLE. The engine was fired "over a dozen times, totaling nearly 10 minutes in duration," so it's clearly handled the major challenge for RDE development with aplomb – that being not to let your engine blow itself to bits.

The engine is built using powder bed fusion 3D printing, incorporating NASA's own GRCop-42 copper alloy, which the agency says is key to its ability to withstand the extreme conditions of sustained detonation without overheating.

At full throttle, says NASA, the RDE produced "over 4,000 pounds of thrust for nearly a minute at an average chamber pressure of 622 pounds per square inch, the highest pressure rating for this design on record." The testing included "successful performance of both deep throttling and internal ignition."

With promising results in the bag, NASA has announced it's scaling up to a fully reusable RDE in the 10,000-pound thrust class, where the team hopes it'll be able to start demonstrating performance benefits over regular rocket engines. You can watch this thing fire in the video below.

Source: NASA

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11 comments
Joy Parr
This looks like a tremendous advance, and some great reporting, thanks!
pete-y
Doesn't my car run on a rotating detonation engine. Great idea but needs a better name.
pbethel
pete-y JANUARY 31, 2023 05:04 AM
Doesn't my car run on a rotating detonation engine. Great idea but needs a better name.
No.
Reciprocating combustion engine in your car.
PBZ
pete-y, it actually doesn't. It's vaguely alluded to in the article, but your car uses combustion rather than detonation. In the automotive world detonation is also known as "knock" and most/all modern engines have "knock sensors" to detect such events so that the engine controller can immediately adjust to avoid this as it will quickly destroy an engine.
paul314
@pete-y internal combustion engines work really hard to maintain combustion instead of detonation. Detonation will get you knocking, which at its worst can destroy an engine.
Maboomba Maboomba
pete-y, Your car engine is based on combustion, not detonation. That's the whole point. If your car engine goes into "detonation", they call it "knock" and it is bad for the engine. Maybe they could use detonation to improve car engines too, but that is a lot of stress on components.
jzj
Gasoline engines are combustion. Diesel engines are detonation. Taking into consideration the greater energy density of diesel v gasoline, diesel engines are nowhere near 25% more efficient.
Username
"knocking in a gas engine is caused by pre-ignition. The fuel ignites before the piston reaches it's proper position. As far as it normally being a "detonation" or combustion, the line becomes somewhat blurry. There is definitely an explosion.
vince
Diesel engines are NOT detonation engines asjzj claims. They are combustion engines which get their spark from compression of gases rather than a spark plug. That 'spark' is not a detonation of fuel...its still combusted with dirty combustion products.
Joy Parr
RDEs seem an excellent fit for both Rocket Lab and Relativity Space, companies which already 3D print their rocket engines. Do you know whether they're working on this design please?