Rotating Combustion coming along

[darthgently]

This is the smoothest and longest run I've seen for this approach.  Looks great

[JoeSchmuckatelli]

First I'm hearing of this.  Is this a possible something to look at improving efficiency of current rocket engines or something else? 

[Nuke]

rotating detonation engines have been something in the news a lot recently. think of it as a ring of pulse detonation engines, but continuously going off one after another in cyclical fashion. i believe they bring the possibility of higher exhaust velocities with chemical engines (better isp). 

Edited January 29, 2023 by Nuke

[JadeOfMaar]

31 minutes ago, JoeSchmuckatelli said:

First I'm hearing of this.  Is this a possible something to look at improving efficiency of current rocket engines or something else? 

It is. All rocket engines so far use a subsonic (deflagration type) combustion technique while detonation is supersonic. This automatically means higher impulse, and the engine itself is virtually free of moving parts, rejects heat better, and is much easier to manufacture. So far all test articles feature an aerospike nozzle. Aerospikes don't care what the ambient pressure is (rather than most engines which have a bell nozzle specializing it for sea level, vacuum or somewhere in-between). If RDEs turn out to only be aerospikes that is arguably a good thing because that's one less engineering variable that the rocket designers need to bother with.

[JoeSchmuckatelli]

1 hour ago, Nuke said:

think of it as a ring of pulse detonation engines, but continuously going off one after another in cyclical fashion.

 

1 hour ago, JadeOfMaar said:

So far all test articles feature an aerospike nozzle.

I'm gonna have to start googling.  I'm not getting a good picture of how this works - but it sounds very interesting.  If I find a good video or animation of how it works - I'll post back in case this kind of engine is as new for others as it is for me.

 

Thanks guys!

[darthgently]

5 minutes ago, JoeSchmuckatelli said:

 

I'm gonna have to start googling.  I'm not getting a good picture of how this works - but it sounds very interesting.  If I find a good video or animation of how it works - I'll post back in case this kind of engine is as new for others as it is for me.

 

Thanks guys!

I missed your original question but answers above cover it very well.  Most tests I've seen of vids of prototypes ran a lot rougher and sputtered out in seconds. 

Not only is the aerospike perfect for this ring shaped supersonic chamber, the ring chamber makes the most sense for an aerospike.  A match made in heaven, higher Isp, less mass, and more compact.  Yay!

[mikegarrison]

31 minutes ago, JoeSchmuckatelli said:

I'm gonna have to start googling.  I'm not getting a good picture of how this works - but it sounds very interesting.  If I find a good video or animation of how it works - I'll post back in case this kind of engine is as new for others as it is for me.

Scott Manley had a decent video on this.

The idea is that the combustion is constant volume rather than constant pressure, which changes the thermodynamic cycle. Rocket engines tend to approximate a Brayton Cycle (same as gas turbine engines), with the combustion happening at (approximately) constant pressure. Detonation happens so quickly that there is no time for the volume to expand, so the pressure spikes up instead (via shockwave).

[JoeSchmuckatelli]

Just now, mikegarrison said:

Scott Manley had a decent video on this.

Thanks - I'll start there!

 

[darthgently]

1 hour ago, JoeSchmuckatelli said:

Thanks - I'll start there!

 

Just imagine a detonation wave circling endlessly around in a ring around the spike.  The ring, or toroidal chamber, is open on the face toward the spike

[JoeSchmuckatelli]

10 minutes ago, darthgently said:

Just imagine a detonation wave circling endlessly around in a ring around the spike.  The ring, or toroidal chamber, is open on the face toward the spike

Until I started looking into that - it was really hard for me to picture.  I kept expecting something mechanical rotating.  Instead, it's the flame front going around the toroidal chamber - which I couldn't wrap my head around with the spike until I saw a video.

Amazing the things folks will come up with!

[kerbiloid]

The galaxies are somebody's rotating combustion engines.

Spoiler

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

Rotating shock waves.

[Shpaget]

8 hours ago, Nuke said:

 think of it as a ring of pulse detonation engines, but continuously going off one after another in cyclical fashion. 

It's not really a boom boom boom thing. It's a single continuous explosion that just keeps on going. As the shock front pases one part of the toroidal combustion chamber, new fuel is injected behind it just in time for that same shock front to come again after making a full lap (actually there are multiple shock fronts chasing each other, but whatever).

[intelliCom]

15 hours ago, darthgently said:

This is the smoothest and longest run I've seen for this approach.  Looks great

Would this mean that rockets of the future don't launch by bell-nozzle engines, but rather 'Rota-Det' ones? That'd be interesting to see.

Edited January 29, 2023 by intelliCom

[Nuke]

4 hours ago, Shpaget said:

It's not really a boom boom boom thing. It's a single continuous explosion that just keeps on going. As the shock front pases one part of the toroidal combustion chamber, new fuel is injected behind it just in time for that same shock front to come again after making a full lap (actually there are multiple shock fronts chasing each other, but whatever).

it was a crude explanation, i was not intending to be extremely accurate. you got a ring of injectors with a shared combustion chamber. i bet the control system to time the valves is pretty awesome. 

[magnemoe]

13 hours ago, JoeSchmuckatelli said:

First I'm hearing of this.  Is this a possible something to look at improving efficiency of current rocket engines or something else? 

It will, gas turbines are less effective than IC engines, mostly because they detonate the fuel. 

[darthgently]

46 minutes ago, intelliCom said:

Would this mean that rockets of the future don't launch by bell-nozzle engines, but rather 'Rota-Det' ones? That'd be interesting to see.

For really big first stages, it probably remains to be seen how scalable the design is given fluidynamics, but I'm optimistic that would be a matter of tweaking.  I'm also wondering, given the compactness, if this  couldn't be incorporated into the aft end spike of a scramjet engine giving it a pure rocket mode

[DDE]

 

The go-to place where the footage was posted was RT's YT channel, which has been nuked from orbit. Not sure where to find the video.

The burn was about a third as long, though.

[darthgently]

5 minutes ago, DDE said:

 

The go-to place where the footage was posted was RT's YT channel, which has been nuked from orbit. Not sure where to find the video.

The burn was about a third as long, though.

That is probably the previous vid I'm remembering.  I also remember reading or listening to something about training a neutral net to control the chamber mix and ignition timing, but not totally sure it was this type of engine or not now 

[DDE]

4 minutes ago, darthgently said:

That is probably the previous vid I'm remembering.  I also remember reading or listening to something about training a neutral net to control the chamber mix and ignition timing, but not totally sure it was this type of engine or not now 

Well, that video definitely predates the neural net hype.

[darthgently]

9 minutes ago, DDE said:

Well, that video definitely predates the neural net hype.

Neural net theory goes back 3 or 4 decades, but yeah, production level AI with them is fairly recent

[sevenperforce]

8 hours ago, darthgently said:

For really big first stages, it probably remains to be seen how scalable the design is given fluidynamics, but I'm optimistic that would be a matter of tweaking.  I'm also wondering, given the compactness, if this  couldn't be incorporated into the aft end spike of a scramjet engine giving it a pure rocket mode

The most promising scramjet designs use a standing oblique wave detonation strategy already, and while that's certainly very efficient, it would be a very different geometry than a rotating combustion rocket engine.

Scramjet engines typically need a very large region for mixing the fuel with the incoming air before it enters the combustion zone (whether shock-induced or from a flameholder) which is another significant difference. However, it would be perfect as the core of an air-augmented rocket, and if the complex physics of a rotation combustion rocket engine could be mastered to the point that it could burn at a range of mixture ratios, then it could even function as a stationary ramjet.

The challenge with airbreathers is generally that even under the most ideal of conditions, the theoretical maximum airspeed of a given design (a) is still only a fraction of orbital velocity and (b) takes place in a high-drag, low-acceleration regime. If you're going to space you need high acceleration, so your switchover engines need to be large enough to provide high acceleration in a high-drag environment, which means they need to be just as heavy as if you were using a pure rocket approach. And then you're almost immediately going to start thinking about an air-launched approach. 

[steve9728]

Meanwhile in Tsinghua University:

https://www.bilibili.com/video/BV14r4y1p7Jp/?spm_id_from=333.788&vd_source=6fef304b8d0c4737896e6b702ddfbfb3

More research papers from this research team:

https://www.labxing.com/lab/75/publications

In fact, they were already finished the maiden flight using RDRE last year. 

Spoiler

On 1/25/2022 at 8:05 AM, steve9728 said:

Tsinghua University has successfully tested their new aspirated supercombustion ram engine.

“The test mission was carried out by a two-stage rocket boosted by the "Qing Hang-Daxing". After the separation of the first stage rocket, the second stage rocket pushed the mission section engine to a predetermined altitude and speed. The engine intake achieved high efficiency suction, the fuel supply system atomised the aviation paraffin into the combustion chamber, the ignition system started smoothly, the combustion chamber entered the intended combustion state, the engine worked stably and obtained continuous thrust, and the test was a complete success.”

"This test at Tsinghua University achieved 'efficient suction in the engine intake tract', which means that the technology verification has been successful and will soon enter the engineering verification stage."

Front, left, right and back of the test rocket.

https://world.huanqiu.com/article/46X3a3161Bj

 

Although the earliest reports at the time did not explicitly state "Yes, we use RDRE", but a later published overview paper points out that (link is full Chinese):

"Tsinghua University has independently designed a new rotary burst ram engine, which has completed its first flight test in January 2022. The flight test obtained the effect of changes in operating environment parameters on the operating characteristics of rotary burst combustion under real flight conditions, confirming the feasibility of rotary burst combustion technology and providing important test data for this technology to move towards engineering and productization. Tsinghua University has also carried out a system solution for a dual-flow multi-ring cavity rotary detonation turbine engine, proposing an isolation section solution to effectively suppress backpressure back propagation and achieving compatibility between the turbomachinery and the rotary detonation combustion chamber."

Edited January 30, 2023 by steve9728

[mikegarrison]

On 1/29/2023 at 5:57 AM, magnemoe said:

It will, gas turbines are less effective than IC engines, mostly because they detonate the fuel. 

There are many things wrong with this statement as written.

The first one is that gas turbines are IC engines. The combustion happens internal to the engine, thus "internal combustion". A steam turbine is not an IC engine because the steam is generated elsewhere (in a separate boiler), but a gas turbine is an IC engine.

Secondly, a Brayton cycle is more efficient than a Diesel cycle (and similarly efficient to an Otto cycle) at the same compression ratio. Diesel cycles can be more thermally efficient than Otto cycle engines because they have higher compression, not because the cycle itself is more efficient.

But there is a lot more to this, such as the power-to-weight ratio of the engines (which usually favors gas turbines), whether the engines can be designed to run at a constant speed or whether they have to be run over a wide range of speeds, how much loss there is between the thermal power output of the engine and the useful power for the application, whether combined cycles can be used (like turbochargers for piston engines or combined cycle powerplants for gas turbines, both of which use the exhaust heat from the main cycle to drive another power cycle).

 

[magnemoe]

Just now, mikegarrison said:

There are many things wrong with this statement as written.

The first one is that gas turbines are IC engines. The combustion happens internal to the engine, thus "internal combustion". A steam turbine is not an IC engine because the steam is generated elsewhere (in a separate boiler), but a gas turbine is an IC engine.

Secondly, a Brayton cycle is more efficient than a Diesel cycle (and similarly efficient to an Otto cycle) at the same compression ratio. Diesel cycles can be more thermally efficient than Otto cycle engines because they have higher compression, not because the cycle itself is more efficient.

But there is a lot more to this, such as the power-to-weight ratio of the engines (which usually favors gas turbines), whether the engines can be designed to run at a constant speed or whether they have to be run over a wide range of speeds, how much loss there is between the thermal power output of the engine and the useful power for the application, whether combined cycles can be used (like turbochargers for piston engines or combined cycle powerplants for gas turbines, both of which use the exhaust heat from the main cycle to drive another power cycle).

Know diesel is more efficient and piston engine would be better than IC. And power to weight turbines win hard and this is critical for flying.  Now the exhaust of an turbine is hot so for an gas power plant you want to add an steam stage who I suspect negate most of the issues as you point out. 

[darthgently]

Good overview of current state of rotating detonation.  The latent contribution of Nikola Tesla's fluid valve concept was surprising to me, but shouldn't have been in hindsight (attn: @JoeSchmuckatelli)