Author Topic: Saving Weight on Engines  (Read 2789 times)

Offline Aeneas

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Saving Weight on Engines
« on: 03/24/2021 03:47 pm »
Dear all,

what is it necessary, to have separate turbo pumps for high end rocket engines? Throttling?

My thoughts are coming from the idea to have an ORSC single shaft set-up for hydrolox engines, to reduce weight on the hydrogen turbo pump. OR cycles are solved. First by the Russians, later, for Raptor and BE-4 by the US-Americans. If single shaft would be possible, you could have the "full flow" in the LOX stream, have an axis crossing the pump area to the LH2 stream and pumping LH2 barely to the required cooling & chamber pressure. Then, you don't have to double that pressure to enable LH2 full flow, still have a cool generator and no problems with bearing purges. Increasing simplicity and TWR.

Since nobody tried it so far, I'm likely wrong in my thoughts. So do you know where?

Offline Oberonian

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Re: Saving Weight on Engines
« Reply #1 on: 03/24/2021 04:25 pm »
Dear all,

what is it necessary, to have separate turbo pumps for high end rocket engines? Throttling?

My thoughts are coming from the idea to have an ORSC single shaft set-up for hydrolox engines, to reduce weight on the hydrogen turbo pump. OR cycles are solved. First by the Russians, later, for Raptor and BE-4 by the US-Americans. If single shaft would be possible, you could have the "full flow" in the LOX stream, have an axis crossing the pump area to the LH2 stream and pumping LH2 barely to the required cooling & chamber pressure. Then, you don't have to double that pressure to enable LH2 full flow, still have a cool generator and no problems with bearing purges. Increasing simplicity and TWR.

Since nobody tried it so far, I'm likely wrong in my thoughts. So do you know where?

How many nozzles would your turbopump feed ?
« Last Edit: 03/24/2021 05:30 pm by Oberonian »

Offline Aeneas

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Re: Saving Weight on Engines
« Reply #2 on: 03/24/2021 04:53 pm »
How many nozzles would your turbopump serve ?

One. Why's that relevant?

Offline Oberonian

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Re: Saving Weight on Engines
« Reply #3 on: 03/24/2021 05:32 pm »
How many nozzles would your turbopump serve ?

One. Why's that relevant?

If you want to save weight...why couldn't one turbo pump feed 4 engines ?
« Last Edit: 03/24/2021 05:33 pm by Oberonian »

Offline Remes

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Re: Saving Weight on Engines
« Reply #4 on: 03/24/2021 07:36 pm »
Dear all,

what is it necessary, to have separate turbo pumps for high end rocket engines? Throttling?

My thoughts are coming from the idea to have an ORSC single shaft set-up for hydrolox engines, to reduce weight on the hydrogen turbo pump.
Hydrogen and Oxygen have different densities. Therefore the pumps typically need to have different speeds. The RL-10 has only one gas turbine, but some gears in between for the different speeds.

Kerolox is fine with one shaft (rd-170/180/...). Similar enough densities.

But the RD-0120 is a single shaft pump. I assume the centrifugal pumps are quite differently designed for both media.

But why going oxydizer rich? Fuel Rich is simpler with hydrogen. Oxydizer rich makes sense with full flow or kerolox (soot).

Offline Oberonian

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Re: Saving Weight on Engines
« Reply #5 on: 03/24/2021 08:02 pm »
Could you in theory have one bigger turbo pump running all 4 nozzles..that have one common gimbal ?

 :)

Offline Remes

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Re: Saving Weight on Engines
« Reply #6 on: 03/24/2021 08:20 pm »
Could you in theory have one bigger turbo pump running all 4 nozzles..that have one common gimbal ?

 :)
The RD-170 that is.

(Edit: it has 4 nozzles, each with an own gimbal. 1 Gimbal would be really huge. A lot of force on a small point in the thrust structure. The Zenith uses the RD-170, and it needs each nozzle to be gimballed individually, otherwsie you can't compensate roll.)
« Last Edit: 03/24/2021 08:24 pm by Remes »

Offline Aeneas

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Re: Saving Weight on Engines
« Reply #7 on: 03/24/2021 08:21 pm »
Dear all,

what is it necessary, to have separate turbo pumps for high end rocket engines? Throttling?

My thoughts are coming from the idea to have an ORSC single shaft set-up for hydrolox engines, to reduce weight on the hydrogen turbo pump.
Hydrogen and Oxygen have different densities. Therefore the pumps typically need to have different speeds. The RL-10 has only one gas turbine, but some gears in between for the different speeds.

Kerolox is fine with one shaft (rd-170/180/...). Similar enough densities.

But the RD-0120 is a single shaft pump. I assume the centrifugal pumps are quite differently designed for both media.

But why going oxydizer rich? Fuel Rich is simpler with hydrogen. Oxydizer rich makes sense with full flow or kerolox (soot).

The idea was, that for FRSC I need ~ double the chamber pressure provided by the pump when burning in full flow. For high volume hydrogen, this means HUGE pumps with lots of MW. RS-25 needs 53 MW for ~74 kg/s hydrogen and just 17 MW for 440 kg/s oxygen. If I outsource the full flow burning into the oxygen stream, I only need to go slightly above chamber pressure in the hydrogen stream, to compensate for cooling system losses. Or is my thinking faulty?

Offline Oberonian

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Re: Saving Weight on Engines
« Reply #8 on: 03/25/2021 03:42 am »
Could you in theory have one bigger turbo pump running all 4 nozzles..that have one common gimbal ?

 :)
The RD-170 that is.

(Edit: it has 4 nozzles, each with an own gimbal. 1 Gimbal would be really huge. A lot of force on a small point in the thrust structure. The Zenith uses the RD-170, and it needs each nozzle to be gimballed individually, otherwsie you can't compensate roll.)

Yes...okay...you learn something new everyday !

 ;D

One gimbal in that would be a new innovation.
« Last Edit: 03/25/2021 03:46 am by Oberonian »

Offline Aeneas

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Re: Saving Weight on Engines
« Reply #9 on: 03/26/2021 08:13 am »
So summarizing we can say, single shaft for hydrolox is possible, if the turbo pumps are designed differently. So, in theory, ORSC for hydrolox is possible, too. Now, still the question is to whether the assumption, this reduces weight or not. I would still say yes, due to much less required pressure in the LH2 stream.

Are there other problems arising from a single shaft? When throttling for example?

 

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