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In the US, a rotating detonation rocket engine takes flight

arstechnica.com

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Re: In the US, a rotating detonation rocket engine takes flight

#21

Post by K0balt »

zdragnar wrote: post #14
casey2 wrote: post #7

2 hours? What's the point? It could be 0 minutes with a 0% explosion rate and the total travel time would probably be longer.

The point is reduced fuel use and faster response times (either emergencies or warfare). Maintaining a detonation (as opposed to deflagration) is quite a technical challenge. If nothing else, it pushes mechanical engineering and material science forward.

At supersonic speeds, the efficiency of an engine like this can be very high, and at high altitudes, travel is very efficient. People don’t seem to get that there is potential for more efficient transport at supersonic speeds/ hypersonic speeds. The ultimate example of this a satellite. How many times does it circle the world every 45 min, all on that initial fuel it took to get it up there? It seems wasteful, but it’s actually the most efficient form of transportation in existence.

Of course, hypersonic transport would not be as efficient as a satellite, but still, at 100k feet, for example, you can go 5000km/h while only consuming the same amount of fuel that you would use to go 300km/h at sea level. The potential for efficiency gains are huge, and the fuel cost of getting to altitude is mostly returned in the descent.

Of course, the technical challenges are also huge, so I don’t expect to see hypersonic airliners any time soon, but when we do get them, they could easily be 6-7x as efficient as existing transports. And it would be nice to have long haul flights be 3x as fast or faster.

People mistakenly assume that this kind of travel only has applications for the military or the elites, and, like air travel in general, that will probably be initially true. But after the rich and the government foots the bill in lives and research to make it safe and economical, it should hold huge gains for society at large.

Science and engineering is one of the only cases where trickle down economics actually kind of works. In knowledge, a rising tide really does lift all boats.

Re: In the US, a rotating detonation rocket engine takes flight

#24

Post by twic »

kd5bjo wrote: post #8
philipodonnell wrote: post #3

Earlier quoted context omitted.

If I’m understanding this correctly, if you set off one bomb the explosion travels at a certain speed, but if you put a bunch of bombs in a circle and set them off one at a time, the very last explosion will be going a lot faster than the first one?

From my understanding, it's more that the explosion phase of a detonation is more fuel-efficient than the burning phase, but can't last very long under normal circumstances because the flame front is moving so fast-- This is a trick to continue fueling the explosion to sustain it over an indefinite time period. Think about it in terms of an old-fashioned gunpowder line fuse: If you lay it out in a ring and have some…

What i've never understood is how detonation can be more efficient than deflagration. What does that mean? Both types of engine take a mix of fuel and oxidiser and turn it into hot combustion products. The hot combustion products then expand through a nozzle to produce thrust. How is that process different between the two? Does a deflagration engine leave some fuel unburnt, that a detonation engine burns? Does the combustion of the same fuel somehow produce more heat? Or less heat but more pressure? Is it something about the expansion?

To put it another way, if you set up a deflagration engine and a detonation engine next to each other, and fed them fuel and oxidiser at the same rate, how would the streams of exhaust gas coming out of them look different? What other external differences would you see?

Re: In the US, a rotating detonation rocket engine takes flight

#25

Post by superkuh »

This is one of the few hypersonic technologies which could actually be enabling. This is because detonation speeds things up and increases range compared to deflagration (burning) without necessarily needing air-breathing added. This means the craft can remain a simple tapered cone traditional rocket and avoid shockwave imgingement sites on the craft air intakes and the thermal load of that that is so far infeasible to maintain for more than a minute or two.

Re: In the US, a rotating detonation rocket engine takes flight

#27

Post by Symmetry »

twic wrote: post #24
kd5bjo wrote: post #8

Earlier quoted context omitted.

From my understanding, it's more that the explosion phase of a detonation is more fuel-efficient than the burning phase, but can't last very long under normal circumstances because the flame front is moving so fast-- This is a trick to continue fueling the explosion to sustain it over an indefinite time period. Think about it in terms of an old-fashioned gunpowder line fuse: If you lay it out in a ring and have some…

What i've never understood is how detonation can be more efficient than deflagration. What does that mean? Both types of engine take a mix of fuel and oxidiser and turn it into hot combustion products. The hot combustion products then expand through a nozzle to produce thrust. How is that process different between the two? Does a deflagration engine leave some fuel unburnt, that a detonation engine burns? Does the co…

The energy produced by the combustion is the same but different fractions of it are converted into work. Just like efficiency differences in other types of heat engine.

Re: In the US, a rotating detonation rocket engine takes flight

#28

Post by pxndxx »

zelos wrote: post #5
ColinWright wrote: post #2

From the article: "In contrast to a traditional rocket engine, in which a highly pressurized propellant and an oxidizer are injected into a combustion chamber where they burn and produce an energetic exhaust plume, a rotating detonation engine is different in that a wave of detonation travels around a circular channel. This is sustained by the injection of fuel and oxidizer and produces a shockwave that travels outwa…

Scott Manley has a great video about them: https://www.youtube.com/watch?v=rG_Eh0J_4_s

Steve Mould has a "rotating flame" video which also helps visualize this: https://www.youtube.com/watch?v=SqhXQUzVMlQ

Re: In the US, a rotating detonation rocket engine takes flight

#29

Post by nfriedly »

magicalhippo wrote: post #4
ColinWright wrote: post #2

From the article: "In contrast to a traditional rocket engine, in which a highly pressurized propellant and an oxidizer are injected into a combustion chamber where they burn and produce an energetic exhaust plume, a rotating detonation engine is different in that a wave of detonation travels around a circular channel. This is sustained by the injection of fuel and oxidizer and produces a shockwave that travels outwa…

Integza made a YouTube video[1] where he visited a lab where they had a RDE, and includes some nice explanations, animations and slow-mos of the prototype in action. His channel has a certain flavor, but at least the video is informative. [1]: https://www.youtube.com/watch?v=fRMMSyCcTDI

> His channel has a certain flavor

It's kind of an anti-tomato flavor.

Re: In the US, a rotating detonation rocket engine takes flight

#30

Post by HeatrayEnjoyer »

growlNark wrote: post #18

> hypersonic This is a meaningless term. There's just varying degrees supersonic. "hyper" implies a completely different thing. EDIT: apparently the military has bastardized the term

Hypersonic begins at 5x speed of sound.
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