5 ms·

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

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 outward at supersonic speed." Nope ... on my way to do web searches to try to figure out what this means. First stop: https://en.wikipedia.org/wiki/Rotating_detonation_engine https://en.wikipedia.org/wiki/Rotating_detonation_engine "A rotating detonation engine (RDE) uses a form of pressure gain combustion, where one or more detonations continuously travel around an annular channel. ... In detonative combustion, the flame front expands at supersonic speed. It is theoretically up to 25% more efficient than conventional deflagrative combustion ... Disadvantages include instability and noise." No images, no animations. OK ... bookmarked, and I'll chase the references later. Edit: OK, here's the best reference I've found so far: https://www.sandboxx.us/news/what-is-a-rotating-detonation-engine-and-what-could-it-mean-for-aviation/ https://www.sandboxx.us/news/what-is-a-rotating-detonation-e... Now back to work.

philipodonnell 1y ago
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?
- kd5bjo 1y ago
  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 kind of mechanism to continuously place down new gunpowder on the ring in front of the flame, you can keep it going until you run out of fuel.
  - twic 1y ago
    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?
    - Symmetry 1y ago
      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.
      - slow_typist 1y ago
        η = 1 - ( T_c / T_h ) Carnot-Efficiency is the theoretical limit of the cycle’s ability to get work out of the thermal energy where T_c is the exhaust (coldest) temperature after expansion and T_h the hottest temperature (before expansion). Temperatures given in K (Kelvin), so 100% if you manage to get T_c to absolute zero temperature.
    - mannykannot 1y ago
      This is mentioned in the introduction here [1]. The version I'm looking at is an image, so I cannot easily copy-paste the relevant passage, but it seems to say that the efficiency gain comes from detonation causing the combustion to occur at a higher pressure than in the case of deflagration. Generally speaking, higher peak pressures increase the efficiency of heat engines, as this allows for greater expansion of the working fluid, and thus more work being done for the same fuel consumption. With regard to your comparison, I guess this means that the detonation engine can have a higher pressure in the combustion chamber, together with a larger bell, a faster-moving exhaust, or some combination. [1] https://arc.aiaa.org/doi/10.2514/6.2013-3971 https://arc.aiaa.org/doi/10.2514/6.2013-3971
- Symmetry 1y ago
  You've got the speed at which a detonation progresses within the explosive material and the speed at which the shock wave travels through the air. Neither is going to change based on the bomb's arrangement. But if you detonate a string of bombs so that each goes as the shock front from the first reaches it you can get, through constructive and destructive interference, a shockwave going mostly in one direction. But that's mostly not related to how this engine works.
magicalhippo 1y ago
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 https://www.youtube.com/watch?v=fRMMSyCcTDI
- nfriedly 1y ago
  > His channel has a certain flavor It's kind of an anti-tomato flavor.
  - gorlilla 1y ago
    What's wrong with tomato degloving by rocket?
zelos 1y ago
Scott Manley has a great video about them: https://www.youtube.com/watch?v=rG_Eh0J_4_s https://www.youtube.com/watch?v=rG_Eh0J_4_s
- coreyh14444 1y ago
  My first thought when I read this: "I bet Scott Manley has a video about this."
  - deleted 1y ago
    [deleted]
- pxndxx 1y ago
  Steve Mould has a "rotating flame" video which also helps visualize this: https://www.youtube.com/watch?v=SqhXQUzVMlQ https://www.youtube.com/watch?v=SqhXQUzVMlQ
Symmetry 1y ago
Those descriptions are actually both correct, but one is describing the elephant's trunk and another the elephant's ear.
- Symmetry 1y ago
  To be a bit more clear, the detonation is racing around a circular track in one plane, but the net thrust is in the direction perpendicular to that plane. Fuel and oxidiser are continuously pumped in all along the track, dropping to ~0 after a detonation and rising afterwards until the detonation front arrives again. Since you don't have to pump into a continual high pressure deflagration like in a conventional rocket engine this looks like it should be easier in terms of pump power. Rocket engine efficiency, like all heat engine efficiency[1], governed by the difference in temperature between hot and cold in the cycle. Because at any given point in a detonation engine the combustion engine only comes in pulses it can reach temperatures that would otherwise melt the rocket engine. That's true of regular rocket engines too, which use active cooling, but seems more true of a detonation engine. And I would guess that the exhaust, already being supersonic, needs less of a chock on the de Laval nozzle to ensure laminar flow. [1] Strictly speaking this only applies to combustion rocket engines. An ion engine, for instance, is a rocket engine but not a heat engine.
  - kragen 1y ago
    By "chock" do you mean "impact"? In English a chock is a rubber wedge you put under a wheel to keep it from rolling, or various similar objects, or the act of using one to keep something from moving: https://en.wiktionary.org/wiki/chock https://en.wiktionary.org/wiki/chock
    - Symmetry 1y ago
      Oops, that should have been "choke".
yread 1y ago
The first reference in the wiki article has a nice animation https://www.rtx.com/news/2025/03/04/more-power-no-moving-parts-rotating-detonation-engine https://www.rtx.com/news/2025/03/04/more-power-no-moving-par...
hammock 1y ago
I imagine an internal combustion engine with a ring of spark plugs firing rapidly in sequence into a nozzle that has fuel/air injected uniformly That is my naive attempt to grok with an analogue, that is probably wrong.
xeonmc 1y ago
Basically it's a turbine engine but the rotating blades are replaced with orbiting shockwaves instead.
- kragen 1y ago
  That makes no sense at all. How do you think a turbine engine works?
  - idiotsecant 1y ago
    This is a very low-information post. It would be more useful if you elaborate civilly on why you disagree with parent post.
- Izikiel43 1y ago
  > Turbine made out of shockwaves That sounds like something out of sci-fi, amazing.
jasrys 1y ago
NASA tested one at Marshall about a year ago: https://www.youtube.com/watch?v=UShD03eG9IU https://www.youtube.com/watch?v=UShD03eG9IU
whatevaa 1y ago
https://youtu.be/RVxgyz_avQM?si=S2gqMXGJfx0tkC7h https://youtu.be/RVxgyz_avQM?si=S2gqMXGJfx0tkC7h
numpad0 1y ago
The most fundamental idea of a detonation engine is that, if you substitute fuel "burning" process with subsonic propagation used in every conventional engines with fuel "explosion" process with supersonic wavefront, the reactions will become more instantaneous and energetic and that improves efficiency. This is the detonation part of detonation engine concept. The rotating part is a solution to the problem that forcing a continuous sustained explosion inside an engine can be complicated. By letting the explosion constantly happening, expanding, and traveling radially across a thin cylindrical gap, it solves such problems as sustained combus-^H^H^H detonation, fuel supply, etc. It's not the only possible type of an engine based on detonation principle, but so far the most promising. Detonating piston engines for cars, for example, are much less promising. Engine part is just regular reaction rocket. It shoots the gas out the back. The faster and heavier the gas, the more reaction force it creates. This isn't the first RDE ever to have been built, fired, or fired in a freefall, but it's finicky and experimental enough that it warrants a news story like this.
- zck 1y ago
  >...if you substitute fuel "burning" process with subsonic propagation used in every conventional engines with fuel "explosion" process with supersonic wavefront... This fragment confused me, because it looks like there are three substitutions. There aren't; there's only one. Read it as: If you substitute fuel burning (which has subsonic propagation, and is used in every conventional engine) with fuel explosion (which has a supersonic wavefront)... The first and third "with" link a noun (the respective process) with a property (how fast it shoots gas out the back). The second "with" is the substitution. English is hard! I'm a native speaker, and I had to take a look at a few webpages to understand just this part! And I'm still left with questions, like why subsonic is described as having "propagation", but supersonic is described as having a "wavefront". Is this a distinction with a difference? I don't know.
  - numpad0 1y ago
    I must admit that I'm in fact not a native English speaker and my sentence construction is still jarring at times... sorry for that. That distinction was not intentional, but IIUC, chemical reactions propagating faster than the speed of sound(of surrounding material, not necessarily of air(which idk how is it even defined, ductile limit or something(of air!?))) has effect of consolidating what would normally be multiple consecutive waves of density changes following one another, into a single shockwave with higher peak pressure, and higher peak pressure in an engine is generally thought to lead to higher exhaust gas velocities and better efficiencies so long that the engine holds. I think this is what some comments mentioning P-V diagrams and Carnot efficiency is meaning to say, except mine is in uneducated terms.
foobarbecue 1y ago
Yeah, that bit about the shockwave in the first quote is a weird thing to say; I suspect LLM use here. All shockwaves "travel outward at supersonic speed."

philipodonnell 1y ago

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?

kd5bjo 1y ago
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 kind of mechanism to continuously place down new gunpowder on the ring in front of the flame, you can keep it going until you run out of fuel.
- twic 1y ago
  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?
  - Symmetry 1y ago
    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.
    - slow_typist 1y ago
      η = 1 - ( T_c / T_h ) Carnot-Efficiency is the theoretical limit of the cycle’s ability to get work out of the thermal energy where T_c is the exhaust (coldest) temperature after expansion and T_h the hottest temperature (before expansion). Temperatures given in K (Kelvin), so 100% if you manage to get T_c to absolute zero temperature.
  - mannykannot 1y ago
    This is mentioned in the introduction here [1]. The version I'm looking at is an image, so I cannot easily copy-paste the relevant passage, but it seems to say that the efficiency gain comes from detonation causing the combustion to occur at a higher pressure than in the case of deflagration. Generally speaking, higher peak pressures increase the efficiency of heat engines, as this allows for greater expansion of the working fluid, and thus more work being done for the same fuel consumption. With regard to your comparison, I guess this means that the detonation engine can have a higher pressure in the combustion chamber, together with a larger bell, a faster-moving exhaust, or some combination. [1] https://arc.aiaa.org/doi/10.2514/6.2013-3971 https://arc.aiaa.org/doi/10.2514/6.2013-3971
Symmetry 1y ago
You've got the speed at which a detonation progresses within the explosive material and the speed at which the shock wave travels through the air. Neither is going to change based on the bomb's arrangement. But if you detonate a string of bombs so that each goes as the shock front from the first reaches it you can get, through constructive and destructive interference, a shockwave going mostly in one direction. But that's mostly not related to how this engine works.

magicalhippo 1y ago

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 https://www.youtube.com/watch?v=fRMMSyCcTDI

nfriedly 1y ago
> His channel has a certain flavor It's kind of an anti-tomato flavor.
- gorlilla 1y ago
  What's wrong with tomato degloving by rocket?

zelos 1y ago

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

coreyh14444 1y ago
My first thought when I read this: "I bet Scott Manley has a video about this."
- deleted 1y ago
  [deleted]
pxndxx 1y ago
Steve Mould has a "rotating flame" video which also helps visualize this: https://www.youtube.com/watch?v=SqhXQUzVMlQ https://www.youtube.com/watch?v=SqhXQUzVMlQ

Symmetry 1y ago

Those descriptions are actually both correct, but one is describing the elephant's trunk and another the elephant's ear.

Symmetry 1y ago
To be a bit more clear, the detonation is racing around a circular track in one plane, but the net thrust is in the direction perpendicular to that plane. Fuel and oxidiser are continuously pumped in all along the track, dropping to ~0 after a detonation and rising afterwards until the detonation front arrives again. Since you don't have to pump into a continual high pressure deflagration like in a conventional rocket engine this looks like it should be easier in terms of pump power. Rocket engine efficiency, like all heat engine efficiency[1], governed by the difference in temperature between hot and cold in the cycle. Because at any given point in a detonation engine the combustion engine only comes in pulses it can reach temperatures that would otherwise melt the rocket engine. That's true of regular rocket engines too, which use active cooling, but seems more true of a detonation engine. And I would guess that the exhaust, already being supersonic, needs less of a chock on the de Laval nozzle to ensure laminar flow. [1] Strictly speaking this only applies to combustion rocket engines. An ion engine, for instance, is a rocket engine but not a heat engine.
- kragen 1y ago
  By "chock" do you mean "impact"? In English a chock is a rubber wedge you put under a wheel to keep it from rolling, or various similar objects, or the act of using one to keep something from moving: https://en.wiktionary.org/wiki/chock https://en.wiktionary.org/wiki/chock
  - Symmetry 1y ago
    Oops, that should have been "choke".

yread 1y ago

The first reference in the wiki article has a nice animation https://www.rtx.com/news/2025/03/04/more-power-no-moving-parts-rotating-detonation-engine https://www.rtx.com/news/2025/03/04/more-power-no-moving-par...

hammock 1y ago

I imagine an internal combustion engine with a ring of spark plugs firing rapidly in sequence into a nozzle that has fuel/air injected uniformly That is my naive attempt to grok with an analogue, that is probably wrong.

xeonmc 1y ago

Basically it's a turbine engine but the rotating blades are replaced with orbiting shockwaves instead.

kragen 1y ago
That makes no sense at all. How do you think a turbine engine works?
- idiotsecant 1y ago
  This is a very low-information post. It would be more useful if you elaborate civilly on why you disagree with parent post.
Izikiel43 1y ago
> Turbine made out of shockwaves That sounds like something out of sci-fi, amazing.

jasrys 1y ago

NASA tested one at Marshall about a year ago: https://www.youtube.com/watch?v=UShD03eG9IU https://www.youtube.com/watch?v=UShD03eG9IU

whatevaa 1y ago

https://youtu.be/RVxgyz_avQM?si=S2gqMXGJfx0tkC7h https://youtu.be/RVxgyz_avQM?si=S2gqMXGJfx0tkC7h

numpad0 1y ago

The most fundamental idea of a detonation engine is that, if you substitute fuel "burning" process with subsonic propagation used in every conventional engines with fuel "explosion" process with supersonic wavefront, the reactions will become more instantaneous and energetic and that improves efficiency. This is the detonation part of detonation engine concept. The rotating part is a solution to the problem that forcing a continuous sustained explosion inside an engine can be complicated. By letting the explosion constantly happening, expanding, and traveling radially across a thin cylindrical gap, it solves such problems as sustained combus-^H^H^H detonation, fuel supply, etc. It's not the only possible type of an engine based on detonation principle, but so far the most promising. Detonating piston engines for cars, for example, are much less promising. Engine part is just regular reaction rocket. It shoots the gas out the back. The faster and heavier the gas, the more reaction force it creates. This isn't the first RDE ever to have been built, fired, or fired in a freefall, but it's finicky and experimental enough that it warrants a news story like this.

zck 1y ago
>...if you substitute fuel "burning" process with subsonic propagation used in every conventional engines with fuel "explosion" process with supersonic wavefront... This fragment confused me, because it looks like there are three substitutions. There aren't; there's only one. Read it as: If you substitute fuel burning (which has subsonic propagation, and is used in every conventional engine) with fuel explosion (which has a supersonic wavefront)... The first and third "with" link a noun (the respective process) with a property (how fast it shoots gas out the back). The second "with" is the substitution. English is hard! I'm a native speaker, and I had to take a look at a few webpages to understand just this part! And I'm still left with questions, like why subsonic is described as having "propagation", but supersonic is described as having a "wavefront". Is this a distinction with a difference? I don't know.
- numpad0 1y ago
  I must admit that I'm in fact not a native English speaker and my sentence construction is still jarring at times... sorry for that. That distinction was not intentional, but IIUC, chemical reactions propagating faster than the speed of sound(of surrounding material, not necessarily of air(which idk how is it even defined, ductile limit or something(of air!?))) has effect of consolidating what would normally be multiple consecutive waves of density changes following one another, into a single shockwave with higher peak pressure, and higher peak pressure in an engine is generally thought to lead to higher exhaust gas velocities and better efficiencies so long that the engine holds. I think this is what some comments mentioning P-V diagrams and Carnot efficiency is meaning to say, except mine is in uneducated terms.

foobarbecue 1y ago

Yeah, that bit about the shockwave in the first quote is a weird thing to say; I suspect LLM use here. All shockwaves "travel outward at supersonic speed."