How Rocket Engine Fuel Injectors Work: Coaxial Swirlers 

Thanks for the update. That's beautiful machine work! A couple of questions, some of which might be impossible to answer until the tests have been run: What temperatures will the swirlers and the mounting plate experience? Can the brass survive the temperature differential between the different tanks and the combustion chamber? Will they be able to withstand the high temperatures if anything fails to go according to plan, in the combustion chamber? Thanks again.

They have both legal and business reasons for that (ie ITAR). But you also have to give credit to SpaceX, RocketLab and many other new space companies for raising the bar in the commercial/government space industry when it comes to transparency. :)

@@CopenhagenSuborbitals That's also true. I appreciate you are reading and replying to comments. All the best!

Information is precious. I do not begrudge SpaceX for keeping things dark. Competition is war.

Well actually, SpaceX are not that secretive

Group thinking is critical to being better than AI. If you got a few hundred people that are all involved in rocket engines to give free input...and there is a lot to gain listening to non rocket scientists, a different perspective and unexpected ideas.

Thank you, Steve! Glad to have you on board. :) Lots of interesting stuff coming up.

Actually the idea of using swirlers in rocket engines have been had before, at least by the pros...

@@jnielsen20 Even SpaceX new Raptor engine use swirlers: twitter.com/elonmusk/status/1132894389095653376?s=19 "Raptor uses a large number of coaxial swirl injectors, which (we believe) achieves highest theoretical mixing/combustion efficiency."

Thank you, Morten! Audio is always a fine balance between getting the best sound and not having the microphone in frame. :) We'll try!

It certainly does! And there is a significant effort in the industry to 3D print this type of injectors, or basically any type of rocket engine injector. Sadly, it is prohibitly expensive for us. Moreover the surface firnish is not quite good enough yet from 3D printing. I will expect some variance between elements of this type if it was made with 3D print.

@@CopenhagenSuborbitals This may be of interest, particularly the ability to transition between alloys on the fly ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-YGQStbaqArY.html

@@CopenhagenSuborbitals I agree it can be prohibitively expensive, out of curiosity what are the operation temperatures that the swirlers must handle?

@@wilsonmura5930 probably pretty cold, given that their core is passing liquid oxygen. Their downstream face will get some IR heating from combustion, but the combustion reaction itself should take place at some distance downstream of the injector exits rather than right at the injection face. This is why injectors (usually) don't need cooling systems like the chamber, they pretty much are their own cooling system.

@@maxk4324 Oka so then, 3D printing it is not a crazy crazy idea?

That's a good question and actually it's something we are trying out as well.

I wonder as well… maybe swirling in the same direction helps the mist diffuse, because when the cones collide they do not cancel their tangential velocities? 🤔

@@DamienPollet usually in rocket engines there are 3 flow regions. Going from injector to nozzle, 1) injection where you want to break up propellants into as tiny droplets as possible, 2) the diffusion flame where most (~99%) of the combustion occurs, and 3) an acceleration region before the nozzle throat where the hot gasses have mostly finshed reacting and are being accelerated up to sonic velocity by the time they reach the throat. For injectors the goal is not usually diffusion but rather to break up the propellant into tiny droplets and to disperse those droplets as uniformly as possible. So in theory, a counter spinning swirl would improve propellant break up into tiny droplets, but I wonder if it would have a negative effect on the distribution uniformity (ie creating ox rich and fuel rich pockets later in the diffusion flame). Its pretty hard to say without running a full engine test or without some next level combustion flow simulation (ie stuff you'd run on supercomputers).

They mention a few comments down that it could improve Fuel/Oxidizer mix due to the increased speed of propellant particle collisions, so it might. They probably have limited budget so trying both out might not be feasible however if I were them and I had budget to spare for such a thing I'd mock up two small scale model test bells one with the normal valves and one with a set of counter-rotating valves and see which one generates better results.

800bar of pressure will do whatever you want lol

That could work well. We have an old ceramics oven on hand though, so we will give it a go in that one first :-)

Behemoth29 probably some small tubing

The lids could probably shrinked in place. But the other seals have to be quite perfect to prevent mixing of LOX and fuel in places you dont want it to mix.

@@CopenhagenSuborbitals I would expect the heat shrink process to produce airtight and strong couplings. In any case, no significant amounts of LOX and fuel will flow in the reverse direction due to differences in pressure.

@@BaldurNorddahl A difference in pressure is exactly what would cause a leak, if the difference is high enough. Unless you're saying that the pressure difference is tiny, which I would contest by pointing out that the fuel will likely be at a much lower pressure since it first has to pass through the combustion chamber cooling jacket

@@maxk4324 The point being that the pressure differences presses this thing together instead of blowing it apart. Any leaks can only go in the direction of the combustion chamber because that has the lowest pressure. The only seal is from the LOX to the fuel part of the swirler and even if some tiny amount of LOX go that way, it could never burn and it could not enter the fuel stream before the swirler.

That is a really good question. We discussed it earlier but seems to have forgotten about it again. Intuitively the increased collision velocity (when moving opposite) should give better atomization. Perhaps we need to ask PH Spaanteknik for another shipment of test elements... :-)

@@CopenhagenSuborbitals oh, ok. I'm a recent subscriber so I'll go back and check videos I missed.

That is where the fuel comes through from the cooling jacket into the injector.

It can be, that's why we have been running on 75% ethanol / 25% water mixture. Adding some water to the fuel lowers its boiling point. Then again, a year ago we've tested up to 92,5% ethanol / 7,5% water with a TEOS additive to the fuel, which deposits an insulating layer on the combustion chamber wall to reduce heat transfer to the regen cooling chamber, and the static tests ran with no issues at those mixtures. That's from this test: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-koSpj1rMdYk.html

No, we are prohibited to export injector technology by law in Denmark.

Should be CW614N.

@@CopenhagenSuborbitals www.holmedodsworth.com/materials/datasheets/brass-datasheets/cz121-cw614n-free-machining-brass Melting Point: 890 C

Why brass though?

Since injectors will be passing liquid through them (one being a cryogenic liquod) whenever combustion is occurring heat should, ideally, not be as big an issue, unless some weird fluid dynamic phenomenon occurs that couldn't have been predicted. Vibration, however, is definitely something to keep an eye on. I wonder if they should make a mock up injector flange and then run a heavy duty vibration test to see if it wears out quickly.

We are not really open source because of those reasons. We do share our developments, but when it comes to critical technologies like guidance or injectors, we don't share much more than you could find in a textbook on google.

@@CopenhagenSuborbitals that's very reasonable