Rotating Explosion Rocket Engine

[Shpaget]

A new type of rocket engine is in the works, where the combustion chamber is an annular ring and fuel and oxydiser are injected from multiple nozzles but not from all the nozzles continuously, rather they are injected in sync with the shock front of the explosion, so the detonation front goes around and around.

This is in contrast to classic rocket engine design where fuel doesn't detonate but deflagrate. We are talking literally about continuous explosion.

They hope to get better engine performance (fuel efficiency, engine mass, ease of construction). I wasn't able to find actual numbers, but this high speed video looks pretty.

 

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.101.013106

https://www.eurekalert.org/pub_releases/2020-02/uow-sfr021820.php

[Scotius]

Hmm. Interesting. Won't it rotate entire rocket during long enough burn?

[Shpaget]

That's a good point. Honestly, I have no idea. The math behind the whole thing is not trivial.

I suppose using multiple engines solves it, but for one engine perhaps diverting a fraction of the exhaust to compensate would still be ok, if the engine itself has a performance advantage over classic design.

[Flying dutchman]

I wonder if the exhaust velocity will be higher.

[mikegarrison]

The efficiency of an engine is related to the pressure at which the combustion happens. This appears to be an attempt to make the combustion happen at a higher pressure.

It's similar to a pulse detonation engine except they convert points in time into points in space by setting up these rotational modes.

Edit: According to the wikipedia article,  the therodynamic cycle advantage is not due to higher pressure, but rather because it is a constant-volume combustion process.

Edited May 1, 2020 by mikegarrison

[magnemoe]

31 minutes ago, Shpaget said:

That's a good point. Honestly, I have no idea. The math behind the whole thing is not trivial.

I suppose using multiple engines solves it, but for one engine perhaps diverting a fraction of the exhaust to compensate would still be ok, if the engine itself has a performance advantage over classic design.

They have worked with explosion jet engines for an long time without much visible success. 
However an rocket engine might actually be easier as jet engines has to handle variable speed and air pressure. 

[Shpaget]

Are you referring to pulsejets such as those used on V-1 flying bombs? They were cheap, low tech devices. I'm not sure how fair it is to compare them to this.

Edited May 1, 2020 by Shpaget

[Elthy]

Is it possible to show the difference between this and a normal rocket engine in a p/v and T/s diagramm? It reminds me of Diesel vs. Otto process, but its propably way more complicated to explain why this can be more efficient.

[Vanamonde]

How does the force not push propellants backwards in the non-firing injectors? 

[mikegarrison]

9 hours ago, Shpaget said:

Are you referring to pulsejets such as those used on V-1 flying bombs? They were cheap, low tech devices. I'm not sure how fair it is to compare them to this.

No, pulse detonation is not the same as a V-1 style pulsejet.

https://en.wikipedia.org/wiki/Pulse_detonation_engine

Edited May 1, 2020 by mikegarrison

[sevenperforce]

Hmm. Hard to figure this out for sure without more data/images but it looks promising. 

Like a continuous fuel-air explosive detonation. 

56 minutes ago, Vanamonde said:

How does the force not push propellants backwards in the non-firing injectors? 

If my guess is right, this combustor is producing a continuous shockwave with an associated choke point, just like the divergence point of a conventional de laval nozzle. So the explosion itself is what forces a low-pressure and high-pressure region. New propellant can be injected behind the shockwave after it passes a particular point. 

It almost reminds me of the V-3 cannon, though the mechanism is different.

Imagine a standard fuel-air explosive. A primer charge has already dispersed the fuel, mixing it with the air, and it ignites from the center. Because of the efficient mixing, the combustion propagates faster than the speed of sound, creating a pressure wave that pushes the flame front further faster and faster. When confined, reflection of these waves means it is shot like a bullet, with the burnt exhaust expanding and rarefying behind it.

You get really high combustion efficiency -- what you would expect from something like full-flow staged combustion -- with no turbopump at all. 

[kerbiloid]

So, previously it got clear why UFO bottoms are blinking (pulse engines), now this explains why their lights are rotating.

[farmerben]

19 hours ago, Vanamonde said:

How does the force not push propellants backwards in the non-firing injectors? 

That would be a huge problem if you suddenly stopped flow in a pipe.  If you redirect it not so much.

I wonder how they construct this mechanism?

On the too simple end, a rotating plate valve could do something.

On the super complex end, add a few hundred flippers controlled by piezzo electric ultra-fast continuous stroke control devices.  Then create a neural network starting with experimental data then running a few gigajillion simulations, every now and then another live test.  Within less than a year of human time, wind up with the most intelligent smoke ring blower on the planet.  

[sevenperforce]

2 hours ago, farmerben said:

That would be a huge problem if you suddenly stopped flow in a pipe.  If you redirect it not so much.

I wonder how they construct this mechanism?

On the too simple end, a rotating plate valve could do something.

On the super complex end, add a few hundred flippers controlled by piezzo electric ultra-fast continuous stroke control devices.  Then create a neural network starting with experimental data then running a few gigajillion simulations, every now and then another live test.  Within less than a year of human time, wind up with the most intelligent smoke ring blower on the planet.  

It's a lot easier than that. You just need one-way pressure-controlled valves. 

[DDE]

There's strong evidence they're not the only ones.

Spoiler

 

Note the arrows.

[kerbiloid]

KSP-2 yet hasn't been released but already got outdated. :(

[Scotius]

1 hour ago, kerbiloid said:

KSP-2 yet hasn't been released but already got outdated.

Don't you worry, there will be DLC's to rectify such problems

[Elthy]

On 5/1/2020 at 12:07 PM, Elthy said:

Is it possible to show the difference between this and a normal rocket engine in a p/v and T/s diagramm? It reminds me of Diesel vs. Otto process, but its propably way more complicated to explain why this can be more efficient.

Scott Manley answered my question without ever reading it

[Shpaget]

15 minutes ago, Elthy said:

Scott Manley answered my question without ever reading it

Don't be so sure he's not lurking these parts, likely even participating.

That area looks to be almost as large as the white one (about 90% according to my pixel count).

Edited May 8, 2020 by Shpaget

[Spacescifi]

1 hour ago, Shpaget said:

Don't be so sure he's not lurking these parts, likely even participating.

 

Shhh.... rumor has it he is not the only well known scifi commentator that does.

Nyrath is known to occasionally drop by.... but I do prefer Scott Manley any day of the week. Same goes for Isaac Arthur.

Edited May 8, 2020 by Spacescifi

[DDE]

18 minutes ago, Spacescifi said:

Nyrath is known to occasionally drop by...

This thread is compromised. Nyrath follows me after my RD-600 letter.

[Spacescifi]

6 minutes ago, DDE said:

This thread is compromised. Nyrath follows me after my RD-600 letter.

 

Whaa-t?

[kerbiloid]

Yes, yes. And every time when somebody takes the pusher plates in vain...

[DDE]

11 hours ago, Spacescifi said:

Whaa-t?

Technically I'm a (one-time) Atomic Rockets contributor.