After setting foot on the Moon, the next destination for humankind is Mars, which presents a whole new set of challenges in speedy, long-distance space travel.
So from what I understand, previous rockets shot exhaust out the back in a cone shape. That essentially sprays the exhaust out kind of like a shotgun.
This adds a donut shaped ring of plasma around the tip of the cone which focuses the exhaust into a tighter stream, more like a laser, improving thrust.
Quite a bit more complicated with important distinctions. The biggest differences are where the combustion is occurring.
So from what I understand, previous rockets shot exhaust out the back in a cone shape. That essentially sprays the exhaust out kind of like a shotgun.
Not really. In a bell nozzle engine (which is the traditional rocket engine everyone knows about), the combustion is happening at the far inside of the bell, and the bell is shaped so that all the fuel is burned inside the bell at a specific air pressure. The thrust is provided by the burned fuel which is traveling at high speed. If the air pressure goes down (because your rocket is now higher), you’re losing unburned fuel out of the bell, and its providing no thrust. This is the limitation of bell nozzles.
Example. These are the essentially the same rocket engine. The one on the left has a smaller bell (called a skirt) because its sized for air pressure at sea level (which is high). The one on the right is size for the vacuum of space where there is essentially no air pressure.
Wouldn’t it be great if there was a single engine that worked great at sea level and equally great in vacuum? That brings us too…
This adds a donut shaped ring of plasma around the tip of the cone which focuses the exhaust into a tighter stream, more like a laser, improving thrust.
Not exactly. What you’re describing is called a regular ** “aerospike” rocket engine**, which some designs do have a cone in the middle. What makes the shape so useful it that air pressure pushes the combustion against the cone (spike) at the perfect degree at sea level and in vacuum so that it is very efficient for burning all the fuel without loss.
The problems with aerospike rocket engines is they are VERY heavy, and that cone in the middle gets CRAZY HOT and has a tendency to melt down while the rocket engine is firing
Neat!
The “neat!” is the engine the article is talking about which you haven’t described yet. This would be the Rotating Detonation Rocket Engine!
To our slow human eyes it kind of looks like a regular aerospike, but if you slow motion it, you’d see that the flame isn’t constant all the way around the cone. A RDE engine has single flame that is racing around the circle and contained by shockwave from the previous combustion.
This also means the cone in the middle stays much cooler, which means it can be made much lighter and not melt down.
It’s also how that fuel is burning - detonation vs deflagration.
Put simply, it’s actually exploding rather than just burning, and by controlling how/when more fuel is injected around the ring, you get a controlled explosion that continuously circles around.
They’re taking about a 30-60% increase in efficiency, which is nuts.
Important note rde’s can have more than one detonation wave, most cfd simulations and prototypes have 2 or 3 chasing each other. The challenge being keeping all of them moving at the same speed so as not to flame out etc…
The coolest thing here is we can remove compressors from engines with this approach. That’s huge complexity just poof gone and weight. And that’s ignoring the efficiency gained from these guys.
So from what I understand, previous rockets shot exhaust out the back in a cone shape. That essentially sprays the exhaust out kind of like a shotgun.
This adds a donut shaped ring of plasma around the tip of the cone which focuses the exhaust into a tighter stream, more like a laser, improving thrust.
Neat!
Quite a bit more complicated with important distinctions. The biggest differences are where the combustion is occurring.
Not really. In a bell nozzle engine (which is the traditional rocket engine everyone knows about), the combustion is happening at the far inside of the bell, and the bell is shaped so that all the fuel is burned inside the bell at a specific air pressure. The thrust is provided by the burned fuel which is traveling at high speed. If the air pressure goes down (because your rocket is now higher), you’re losing unburned fuel out of the bell, and its providing no thrust. This is the limitation of bell nozzles.
Example. These are the essentially the same rocket engine. The one on the left has a smaller bell (called a skirt) because its sized for air pressure at sea level (which is high). The one on the right is size for the vacuum of space where there is essentially no air pressure.
Wouldn’t it be great if there was a single engine that worked great at sea level and equally great in vacuum? That brings us too…
Not exactly. What you’re describing is called a regular ** “aerospike” rocket engine**, which some designs do have a cone in the middle. What makes the shape so useful it that air pressure pushes the combustion against the cone (spike) at the perfect degree at sea level and in vacuum so that it is very efficient for burning all the fuel without loss.
The problems with aerospike rocket engines is they are VERY heavy, and that cone in the middle gets CRAZY HOT and has a tendency to melt down while the rocket engine is firing
The “neat!” is the engine the article is talking about which you haven’t described yet. This would be the Rotating Detonation Rocket Engine!
To our slow human eyes it kind of looks like a regular aerospike, but if you slow motion it, you’d see that the flame isn’t constant all the way around the cone. A RDE engine has single flame that is racing around the circle and contained by shockwave from the previous combustion.
This also means the cone in the middle stays much cooler, which means it can be made much lighter and not melt down.
It’s also how that fuel is burning - detonation vs deflagration.
Put simply, it’s actually exploding rather than just burning, and by controlling how/when more fuel is injected around the ring, you get a controlled explosion that continuously circles around.
They’re taking about a 30-60% increase in efficiency, which is nuts.
deleted by creator
Neat!
I have nothing to contribute here, except to give thanks for a high quality post 👍
Important note rde’s can have more than one detonation wave, most cfd simulations and prototypes have 2 or 3 chasing each other. The challenge being keeping all of them moving at the same speed so as not to flame out etc…
Edit: https://www.researchgate.net/figure/Rotating-detonation-engine-with-two-shocks_fig1_323353046
The coolest thing here is we can remove compressors from engines with this approach. That’s huge complexity just poof gone and weight. And that’s ignoring the efficiency gained from these guys.
Neat!
Oh man RDREs are so cool! the other commenter explained it better than I ever could but also here are some great videos about it for further fun!
ETA: I forgot the coolest one! NASA’s own test video