Okay. Detonation Engine is definitely the title of my next sci-fi spaceship action novel. Any of you astrophysicist nerds want to tell us how this locus of concentrated violence works?
Okay. Detonation Engine is definitely the title of my next sci-fi spaceship action novel.
Any of you astrophysicist nerds want to tell us how this locus of concentrated violence works?
Not an astrophysicist but I did do some surface level work with rotating detonation engines in college. Most air breathing engines have 4 stages: Draw air in. Compress that air. Detonate that air...
Exemplary
Not an astrophysicist but I did do some surface level work with rotating detonation engines in college.
Most air breathing engines have 4 stages:
Draw air in.
Compress that air.
Detonate that air with some fuel.
Propel that air out the back to produce thrust
(1. Suck 2. Squeeze 3. Bang 4. Blow)
Rotating detonation engines simplify that to 3 phases by sort of combining the detonation and compression phases.
The basic idea is you start an explosion or detonation in one spot in between two concentric cylinders, like an elongated hollow donut. That explosion travels around the annular channel in the cylinder and as it goes the shockwave in front of the explosion compresses the gas ahead of it priming that gas for the explosion just like you would in a piston engine on the compression stroke or in a jet engine with a compressor stage but in this case there are no moving parts required. The detonation is self sustaining as it travels around the cylinder over and over compressing the air in front of it and then blowing it up as long as it has fuel. You channel the resulting energy from the detonation out one end of the cylinder and you produce thrust. Again no moving parts required on the back end such as a turbine stage because you don’t have any parts requiring movement for the compression stage.
This page has a really simple graphic that shows the idea and probably explains things much better than I just did although in the context of its potential use for military munitions.
Edit: This appears to be a video of the test (although not from an official source - NASA only had shorter test videos) and is pretty awesome.
That test video you linked is awesome! I remember ~3y ago Scott Manley made a video talking about RDEs and talked about some of the challenges with them; crazy to see only a few years later a real...
That test video you linked is awesome! I remember ~3y ago Scott Manley made a video talking about RDEs and talked about some of the challenges with them; crazy to see only a few years later a real long-duration test of one!
Detonation is the supersonic version of combustion. Detonation is more efficient than subsonic combustion, but the conditions it reliably occurs in are specific and still under research. In...
Detonation is the supersonic version of combustion. Detonation is more efficient than subsonic combustion, but the conditions it reliably occurs in are specific and still under research.
In current rocket and jet engines, the "flame front" advances along a suitable flow of oxidiser and fuel at subsonic speeds. Proportional to the rate at which new fuel and oxidiser are being injected.
Assuming you can create the conditions for a detonation reaction, you could imagine for the reaction to be continuous, the propellants would need to be injected at supersonic speeds. Or the flame front would reach the injector and no longer be "supersonic".
A rotating detonation engine solves this problem by advancing the flame front around a closed loop. By the time the supersonic combustion reaction is back to where it started, fresh propellants have been injected.
The loop is visible in the video as the glowing ring. The side of the loop is cut away to make the engines exhaust.
Injecting propellants at supersonic speeds is done in scramjets. I'm interested to hear if someone knows why there are no rocket engines that work like that.
Do you have a reference that explains this from a thermodynamics and/or combustion chemistry perspective? Edit : https://aerospaceamerica.aiaa.org/departments/increasing-engine-efficiency/ Seems...
Detonation is the supersonic version of combustion. Detonation is more efficient than subsonic combustion, but the conditions it reliably occurs in are specific and still under research.
Do you have a reference that explains this from a thermodynamics and/or combustion chemistry perspective?
Seems to be targeting earth atmosphere flight rather than rocket motors that would put things into space.
From OP’s article which is for space:
Looks like it’s an aerospike design, which would in theory work well both in atmosphere and vacuum. I imagine the increased efficiency comes from detonation producing a higher exhaust speed.
For one, you’re using the pressure/temperature rise from the detonation wave itself to heat and compress the fresh fuel air mixture. Compressors use a series of veins and channels which have...
For one, you’re using the pressure/temperature rise from the detonation wave itself to heat and compress the fresh fuel air mixture. Compressors use a series of veins and channels which have efficiency losses to do this:
This engine is missing a big axial compressor because this is a rocket engine. An air-breathing RDE (eg for use on an aircraft) would require the intake air to be compressed somehow.
This engine is missing a big axial compressor because this is a rocket engine.
An air-breathing RDE (eg for use on an aircraft) would require the intake air to be compressed somehow.
No I don't have a good source for the mechanism that allows detonation to have a higher efficiency. After looking for papers I'm not even sure a thermodynamic cycle has been agreed upon. My...
No I don't have a good source for the mechanism that allows detonation to have a higher efficiency. After looking for papers I'm not even sure a thermodynamic cycle has been agreed upon.
My intuition says there isn't enough time for the reactants to move away from the combustion, maybe this increases the pressure ratio?
Also the way in which the reaction spins around the RDE would allow the peak temperature to be higher before the engine starts to melt.
The exhaust speed wouldn't necessarily be increased under detonation, from my understanding. Detonation occurs when combustion moves across an area faster than the speed of sound, but the actual reactants may not move at all.
Like a trail of gunpowder burning across the ground, the gunpowder itself is not moving, but the reaction has a speed.
As a science fiction author currently singing lead vocals in a rock cover band I concur. My best renditions so far are Yellow by Coldplay and The Narcissist by Blur. But as an SF author, I’ve been...
As a science fiction author currently singing lead vocals in a rock cover band I concur.
My best renditions so far are Yellow by Coldplay and The Narcissist by Blur.
But as an SF author, I’ve been developing a live stage show called Space Opera for a looong time…
NASA just put its new propulsion system to the test, powering a 3D-printed rotating detonation rocket engine for a sustained burn that lasted three times as long as the first test.
According to this StackExchange answer, an earlier NASA test had an ISP of ~127s. Honestly kind of interesting; I had assumed they would have better efficiency but apparently their main advantage...
According to this StackExchange answer, an earlier NASA test had an ISP of ~127s. Honestly kind of interesting; I had assumed they would have better efficiency but apparently their main advantage is that they can work with lower compression pressures, which is great for engineering.
Does anyone have more info on the print process? As cool as the engine tech is I can't wrap my head around the print process. Is it an iterative add/subtract, print followed by cutting? Is it sub...
Does anyone have more info on the print process?
As cool as the engine tech is I can't wrap my head around the print process. Is it an iterative add/subtract, print followed by cutting? Is it sub assembly prints? Something else? The stress seems like an extreme boundary in print processes I'm familiar with.
It's an additive process, printing likely very close to final dimensions using blown powder laser cladding, which is pretty high resolution and also friendly to all sorts of space-friendly exotic...
It's an additive process, printing likely very close to final dimensions using blown powder laser cladding, which is pretty high resolution and also friendly to all sorts of space-friendly exotic materials. You can see in the video linked from that page they're forming complex and fine structures during printing, which suggests minimal post-processing is needed. They're almost certainly printing as much of the part in a single pass as they can, my guess is that if they have good temperature control they should be able to achieve reasonably consistent grain/crystal structure over the entire part (although exotic aerospace materials are probably weird anyway, so my guess could be way off)
directed energy deposition. This method uses a mechanical multi-axis arm to deposit material onto a surface. It then uses lasers to melt, deposit, and solidify the material into a structure
Sounds like a weird combination of other printing methods but I'd also like more info.
The Real Engineering video on the engine has a little more detail on the production process. Not a lot though. Laser cladding is, as I understand it, a fairly common industrial process - you can...
Laser cladding is, as I understand it, a fairly common industrial process - you can google for lots of details from commercial operators. I'm sure NASA have some aerospace specific refinements but there's really not that much to refine.
Okay. Detonation Engine is definitely the title of my next sci-fi spaceship action novel.
Any of you astrophysicist nerds want to tell us how this locus of concentrated violence works?
Not an astrophysicist but I did do some surface level work with rotating detonation engines in college.
Most air breathing engines have 4 stages:
(1. Suck 2. Squeeze 3. Bang 4. Blow)
Rotating detonation engines simplify that to 3 phases by sort of combining the detonation and compression phases.
The basic idea is you start an explosion or detonation in one spot in between two concentric cylinders, like an elongated hollow donut. That explosion travels around the annular channel in the cylinder and as it goes the shockwave in front of the explosion compresses the gas ahead of it priming that gas for the explosion just like you would in a piston engine on the compression stroke or in a jet engine with a compressor stage but in this case there are no moving parts required. The detonation is self sustaining as it travels around the cylinder over and over compressing the air in front of it and then blowing it up as long as it has fuel. You channel the resulting energy from the detonation out one end of the cylinder and you produce thrust. Again no moving parts required on the back end such as a turbine stage because you don’t have any parts requiring movement for the compression stage.
This page has a really simple graphic that shows the idea and probably explains things much better than I just did although in the context of its potential use for military munitions.
Edit: This appears to be a video of the test (although not from an official source - NASA only had shorter test videos) and is pretty awesome.
That test video you linked is awesome! I remember ~3y ago Scott Manley made a video talking about RDEs and talked about some of the challenges with them; crazy to see only a few years later a real long-duration test of one!
Detonation is the supersonic version of combustion. Detonation is more efficient than subsonic combustion, but the conditions it reliably occurs in are specific and still under research.
In current rocket and jet engines, the "flame front" advances along a suitable flow of oxidiser and fuel at subsonic speeds. Proportional to the rate at which new fuel and oxidiser are being injected.
Assuming you can create the conditions for a detonation reaction, you could imagine for the reaction to be continuous, the propellants would need to be injected at supersonic speeds. Or the flame front would reach the injector and no longer be "supersonic".
A rotating detonation engine solves this problem by advancing the flame front around a closed loop. By the time the supersonic combustion reaction is back to where it started, fresh propellants have been injected.
The loop is visible in the video as the glowing ring. The side of the loop is cut away to make the engines exhaust.
Injecting propellants at supersonic speeds is done in scramjets. I'm interested to hear if someone knows why there are no rocket engines that work like that.
Do you have a reference that explains this from a thermodynamics and/or combustion chemistry perspective?
Edit : https://aerospaceamerica.aiaa.org/departments/increasing-engine-efficiency/
Seems to be targeting earth atmosphere flight rather than rocket motors that would put things into space.
From OP’s article which is for space:
Looks like it’s an aerospike design, which would in theory work well both in atmosphere and vacuum. I imagine the increased efficiency comes from detonation producing a higher exhaust speed.
For one, you’re using the pressure/temperature rise from the detonation wave itself to heat and compress the fresh fuel air mixture. Compressors use a series of veins and channels which have efficiency losses to do this:
http://www.jmcampbell.com/tip-of-the-month/2015/07/how-to-estimate-compressor-efficiency/
And a paper on thermo models of detonation cycles:
https://arc.uta.edu/publications/cp_files/2645.pdf
This engine is missing a big axial compressor because this is a rocket engine.
An air-breathing RDE (eg for use on an aircraft) would require the intake air to be compressed somehow.
No I don't have a good source for the mechanism that allows detonation to have a higher efficiency. After looking for papers I'm not even sure a thermodynamic cycle has been agreed upon.
My intuition says there isn't enough time for the reactants to move away from the combustion, maybe this increases the pressure ratio?
Also the way in which the reaction spins around the RDE would allow the peak temperature to be higher before the engine starts to melt.
The exhaust speed wouldn't necessarily be increased under detonation, from my understanding. Detonation occurs when combustion moves across an area faster than the speed of sound, but the actual reactants may not move at all.
Like a trail of gunpowder burning across the ground, the gunpowder itself is not moving, but the reaction has a speed.
Real Engineering made a video on this technology about 8 months ago.
He does a good job of explaining the concept. It's really cool.
I was expecting you to say it would be the name of your next rock band. Or maybe your next sci fi rock band.
As a science fiction author currently singing lead vocals in a rock cover band I concur.
My best renditions so far are Yellow by Coldplay and The Narcissist by Blur.
But as an SF author, I’ve been developing a live stage show called Space Opera for a looong time…
Since I play a bit of ksp I tend to jump to finding out the ISP of an engine. How does it look for these engines at this stage?
According to this StackExchange answer, an earlier NASA test had an ISP of ~127s. Honestly kind of interesting; I had assumed they would have better efficiency but apparently their main advantage is that they can work with lower compression pressures, which is great for engineering.
Does anyone have more info on the print process?
As cool as the engine tech is I can't wrap my head around the print process. Is it an iterative add/subtract, print followed by cutting? Is it sub assembly prints? Something else? The stress seems like an extreme boundary in print processes I'm familiar with.
It's an additive process, printing likely very close to final dimensions using blown powder laser cladding, which is pretty high resolution and also friendly to all sorts of space-friendly exotic materials. You can see in the video linked from that page they're forming complex and fine structures during printing, which suggests minimal post-processing is needed. They're almost certainly printing as much of the part in a single pass as they can, my guess is that if they have good temperature control they should be able to achieve reasonably consistent grain/crystal structure over the entire part (although exotic aerospace materials are probably weird anyway, so my guess could be way off)
From @mat 's link
Sounds like a weird combination of other printing methods but I'd also like more info.
The Real Engineering video on the engine has a little more detail on the production process. Not a lot though.
Laser cladding is, as I understand it, a fairly common industrial process - you can google for lots of details from commercial operators. I'm sure NASA have some aerospace specific refinements but there's really not that much to refine.