"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.
"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:
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.
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 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.
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?
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.
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.
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.
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.
>Sassie Duggleby and her husband, Andrew Duggleby, founded Venus Aerospace nearly five years ago with the long-term goal of developing powerful rotating detonation engines and building a hypersonic aircraft that could carry perhaps a dozen passengers and travel at astonishingly fast speeds worldwide.
As an engineering project it sounds really cool, but is the application really commercial travel? I would have thought the military would be far more interested and much better funded.
It's a smokescreen for hypersonic missile development. It's a common tactic. I knew someone who worked on a novel satellite surveillance system. Their pitch was that it would allow them to engage in futures trading because the resolution of their satellites would allow unique insights into global trade for certain markets using realtime optical imaging.
The guy was former Lockheed. One night at dinner I told him to cut the BS and that their real goal was to target military/government contracts. He said "off the record" this is correct. This an unspoken goal by everyone involved - management, investors, etc.
My understanding is it can be hard to position yourself as a defense company as a start up if you don't already have a foothold in the space.
"We're actively engaged with US defense and national security agencies as well as commercial partners exploring hypersonic applications in logistics, aerospace, and future mobility—including large primes," she said. "The enthusiasm we’re seeing reflects a broad recognition that Venus’s technology can unlock new operational and economic possibilities across multiple markets."
Still trying to wrap my head around this. Doesn’t this cause insane stresses with basically all explosions being off axis? Or are there multiple sets of explosions moving at same the on opposites sides?
The main drawback is that RDEs need substantially stronger structure to smooth out the forces. It's still worth it, the force of the detonation (it's not separate explosions, it's a single continuous detonation front moving in a circular channel) is small enough to be containable.
There have been tests with multiple detonation fronts, but controlling them is much harder. It's very hard to have them go around the channel at exactly the same speed, so their positions relative to each other remain fixed.
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.
Fuel efficiency is the answer for "why would you do this?" That's really important for rockets, since to launch each gram of fuel you have to have some more fuel which you also have to lift.
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.
Presumably, you have to be travelling quite a distance before hypersonic/high-altitude flight becomes more efficient than current commercial airliners.
It's not a new term, and it exists because there are unique practical engineering problems associated with high mach numbers so having a term for this regime is useful even if the distinction seems arbitrary from a pure theoretically perspective.
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
"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-e...
Now back to work.
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
My first thought when I read this: "I bet Scott Manley has a video about this."
Basically it's a turbine engine but the rotating blades are replaced with orbiting shockwaves instead.
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.
The first reference in the wiki article has a nice animation
https://www.rtx.com/news/2025/03/04/more-power-no-moving-par...
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 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.
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?
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
Just think in terms of the P-V diagram, you want the pressure increase curve to be as vertical as possible to maximize the area enclosed by the cycle
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.
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.
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.
Those descriptions are actually both correct, but one is describing the elephant's trunk and another the elephant's ear.
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.
>Sassie Duggleby and her husband, Andrew Duggleby, founded Venus Aerospace nearly five years ago with the long-term goal of developing powerful rotating detonation engines and building a hypersonic aircraft that could carry perhaps a dozen passengers and travel at astonishingly fast speeds worldwide.
As an engineering project it sounds really cool, but is the application really commercial travel? I would have thought the military would be far more interested and much better funded.
It's a smokescreen for hypersonic missile development. It's a common tactic. I knew someone who worked on a novel satellite surveillance system. Their pitch was that it would allow them to engage in futures trading because the resolution of their satellites would allow unique insights into global trade for certain markets using realtime optical imaging.
The guy was former Lockheed. One night at dinner I told him to cut the BS and that their real goal was to target military/government contracts. He said "off the record" this is correct. This an unspoken goal by everyone involved - management, investors, etc.
My understanding is it can be hard to position yourself as a defense company as a start up if you don't already have a foothold in the space.
From the bottom of the article:
"We're actively engaged with US defense and national security agencies as well as commercial partners exploring hypersonic applications in logistics, aerospace, and future mobility—including large primes," she said. "The enthusiasm we’re seeing reflects a broad recognition that Venus’s technology can unlock new operational and economic possibilities across multiple markets."
What are ‘large primes’ here?
Primary defense contractors. Lockheed, Boeing, Raytheon, etc.
M136,279,841 is pretty big..
How do you restart after flameout?
Still trying to wrap my head around this. Doesn’t this cause insane stresses with basically all explosions being off axis? Or are there multiple sets of explosions moving at same the on opposites sides?
The main drawback is that RDEs need substantially stronger structure to smooth out the forces. It's still worth it, the force of the detonation (it's not separate explosions, it's a single continuous detonation front moving in a circular channel) is small enough to be containable.
There have been tests with multiple detonation fronts, but controlling them is much harder. It's very hard to have them go around the channel at exactly the same speed, so their positions relative to each other remain fixed.
https://youtu.be/QR6iFVj_xHw?feature=shared Here's a good webinar with some visualization if you're interested in learning more.
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.
JAXA flew one in 2021, to give a sense of developmental pace.
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.
Fuel efficiency is the answer for "why would you do this?" That's really important for rockets, since to launch each gram of fuel you have to have some more fuel which you also have to lift.
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.
Presumably, you have to be travelling quite a distance before hypersonic/high-altitude flight becomes more efficient than current commercial airliners.
Press release videos - https://drive.google.com/drive/folders/194_lxE-vy_ha7-5V_wFj...
Their YouTube is insanely technical, I think, lots of videos with big equations anyway - https://www.youtube.com/@venusaerospace/videos
> 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
It's not a new term, and it exists because there are unique practical engineering problems associated with high mach numbers so having a term for this regime is useful even if the distinction seems arbitrary from a pure theoretically perspective.
Hypersonic begins at 5x speed of sound.