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Re: Vortex rocket engine: lighter, more efficient, more reusable

Posted: Wed Jul 31, 2019 8:05 am
by Giorgio
Maui wrote:I guess I would be curious to know comparatively how much of a problem heat is in the turbines vs the combustion chamber.
Heat in turbines has always represented the majority of engineering headaches. Any increase in temperature effects the very basic proprieties of any metal. In the case of a rocket turbine pump the most important are: resistance, fatigue, tolerances, chemical stability, abrasion.
Modern metallurgical knowledge enables us to design with quite an high degree of confidence metals that can withstand at least 2 of these conditions for a rocket turbine pump application, but not all the 5 of them. Hence reducing even of a small amount the temperature into the turbine chamber makes quite a big difference in the turbine assembly complexity and reliability.

The combustion chamber on the other hand is static, so even if the temperature is higher than in the turbine pump assembly we can use other ways to improve reliability and/or limit heat influence, like boundary layer flow control, regenerative cooling, or the Vortex concept idea.

I would say that with today metallurgical knowledge, 95% of all heat related problems in a rocket engine are focused on the turbo pump side, so any improvement there brings lot of benefits everywhere else, and that's the reason why SpaceX is going for the the full flow/staged combustion/regenerative cooling Raptor Engine.

Just consider that the actual Merlin engine turbo pump section is running at 1350 'C, while the Raptor has a projected mean combustion temperature of around 500 'C in the 2 turbo pumps assembly. It's a huge thermal difference.
They are running cool enough to allow them to increase the pressure to the turbine head up to an incedible 650 Bar, which in turn will allow them to reach the expected 300 Bar in the combustion chamber.

They will need for sure some time to characterize the turbines behavior and their life evolution before they reach that target, but there is no real engineering issue to prevent them from reaching it, and that's why most people are so excited about the Raptor.

Re: Vortex rocket engine: lighter, more efficient, more reusable

Posted: Wed Jul 31, 2019 5:10 pm
by Maui
Wow! That's a much better answer than I was expecting. Thanks!

Re: Vortex rocket engine: lighter, more efficient, more reusable

Posted: Thu Aug 01, 2019 9:12 am
by Giorgio
My pleasure, and glad if it clarified some doubts.

Re: Vortex rocket engine: lighter, more efficient, more reusable

Posted: Wed Sep 06, 2023 8:56 am
by KitemanSA
Giorgio wrote:
Wed Jul 31, 2019 8:05 am

They are running cool enough to allow them to increase the pressure to the turbine head up to an incedible 650 Bar, which in turn will allow them to reach the expected 300 Bar in the combustion chamber.
SpaceX recently ran Raptor 3 at a sustained 350 bar. Not bad!

Re: Vortex rocket engine: lighter, more efficient, more reusable

Posted: Wed Sep 06, 2023 2:17 pm
by Giorgio
KitemanSA wrote:
Wed Sep 06, 2023 8:56 am
SpaceX recently ran Raptor 3 at a sustained 350 bar. Not bad!
Yes, and it's an amazing engineering achievement. I doubt they will be able to improve more without some new and radical discovery in metallurgy and material composition, and so far I do not see any in the various publications.

If they can keep it stable and reliable it could become the workhorse engine for the next decade or more with its 2.7 MN of thrust.

Re: Vortex rocket engine: lighter, more efficient, more reusable

Posted: Wed Sep 06, 2023 2:35 pm
by KitemanSA
Giorgio wrote:
Wed Sep 06, 2023 2:17 pm
KitemanSA wrote:
Wed Sep 06, 2023 8:56 am
SpaceX recently ran Raptor 3 at a sustained 350 bar. Not bad!
Yes, and it's an amazing engineering achievement. I doubt they will be able to improve more without some new and radical discovery in metallurgy and material composition, and so far I do not see any in the various publications.

If they can keep it stable and reliable it could become the workhorse engine for the next decade or more with its 2.7 MN of thrust.
About a year ago, I read they had two alloys they were working with, (monel?)300 and 500. From the article, I got the impression the they were using the “300” alloy in Raptor 2. So, perhaps they are using the “500” alloy in R3. I haven’t heard anything about a “700” alloy, so you could be right.

Re: Vortex rocket engine: lighter, more efficient, more reusable

Posted: Fri Oct 27, 2023 5:23 pm
by KitemanSA
Giorgio wrote:
Wed Sep 06, 2023 2:17 pm
If they can keep it stable and reliable it could become the workhorse engine for the next decade or more with its 2.7 MN of thrust.
It would not surprise me if the plan was to run the Raptor 3 @~85% power (Raptor 2 level) and use the excess for fast turn around margin. Also, they can use the excess for “engine out” redundancy. It would also be available if they just HAD to launch 250tonnes at one time.

The question of economics is whether 10 launches out of the engines while pushing the limits is better than 50 launches at a low stress pace.

Re: Vortex rocket engine: lighter, more efficient, more reusable

Posted: Fri Oct 27, 2023 8:13 pm
by Giorgio
KitemanSA wrote:
Fri Oct 27, 2023 5:23 pm
It would not surprise me if the plan was to run the Raptor 3 @~85% power (Raptor 2 level) and use the excess for fast turn around margin. Also, they can use the excess for “engine out” redundancy. It would also be available if they just HAD to launch 250tonnes at one time.

The question of economics is whether 10 launches out of the engines while pushing the limits is better than 50 launches at a low stress pace.
These are all good point but I guess the only way to answer them would be to put our hands on the real test data that they are executing. My concern is mainly on the corrosion limitation of the Oxygen rich side of the engine flow (especially the turbopump).
Solving that is the key to reliability in my opinion, much more than the extra stress on the alloy due to the increased pressure.

Re: Vortex rocket engine: lighter, more efficient, more reusable

Posted: Fri Oct 27, 2023 9:20 pm
by KitemanSA
Giorgio wrote:
Fri Oct 27, 2023 8:13 pm
… My concern is mainly on the corrosion limitation of the Oxygen rich side of the engine flow (especially the turbopump).
Solving that is the key to reliability in my opinion, much more than the extra stress on the alloy due to the increased pressure.
Seems to me that the corrosion (erosion?) rate would be proportional to the pressure which is why I think they may run at reduced pressure to get more flights without expensive between flight inspections. Remember, they want to fly like an airline, and that means many flights between inspection and refurb. ICBW.

Re: Vortex rocket engine: lighter, more efficient, more reusable

Posted: Sat Oct 28, 2023 6:09 am
by Giorgio
KitemanSA wrote:
Fri Oct 27, 2023 9:20 pm
Seems to me that the corrosion (erosion?) rate would be proportional to the pressure which is why I think they may run at reduced pressure to get more flights without expensive between flight inspections. Remember, they want to fly like an airline, and that means many flights between inspection and refurb. ICBW.
Of course is erosion, not corrosion, but the autocorrect thought he knew better :mrgreen:
Erosion rate for the same alloy is indeed proportional to pressure, as well as temperature and flow rate. The predominant factors are generally dependent on the alloy characteristics and are determined experimentally, so these are again data that only SpaceX has.