Author Topic: Rocket Engine Q&A  (Read 382936 times)

Offline baldusi

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Re: Rocket Engine Q&A
« Reply #440 on: 07/02/2012 11:41 am »
The Japanese have their bleed expander cycle, which is replacing the GG of the open cycle with the expander, but still dumping the gases after they've passed through the turbine, in an open cycle. Apparently they can take it to something like 1,500kN. I guess it won't have good T/W, then?

Offline strangequark

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Re: Rocket Engine Q&A
« Reply #441 on: 07/02/2012 04:13 pm »
The Japanese have their bleed expander cycle, which is replacing the GG of the open cycle with the expander, but still dumping the gases after they've passed through the turbine, in an open cycle. Apparently they can take it to something like 1,500kN. I guess it won't have good T/W, then?

Do you have a reference for that? I know about the LE-5B, but that's RL-10 class. I have heard about expander bleeds hypothetically going to higher thrust (which makes sense, you can have a much higher pressure ratio across the turbine), but I'm not aware of any high thrust production engines that use expander bleed.

As for T/W, LE-5B is about 50, which is in line with RL-10.

Offline baldusi

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Re: Rocket Engine Q&A
« Reply #442 on: 07/02/2012 04:32 pm »
Can't really remember where did I found this papers. I think it was Mitsubishi Heavy Industries Annual Technology discussion, or something like that. Please bear in mind that this is open cycle expander, not close cycle.

Offline gin455res

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Re: Rocket Engine Q&A
« Reply #443 on: 07/29/2012 08:32 pm »
How much of an engine's throttlability is due to nozzle constraints and how much is due to the pump?

And can multi-chambered engines with a single pump, stop the flow to individual chambers to increase throttlability (assuming a pump has a significantly wider power range than a single nozzle can except without the flow separating)?

Offline Robotbeat

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Re: Rocket Engine Q&A
« Reply #444 on: 07/30/2012 07:40 pm »
It's usually the injector design and the chamber design that affect throttleability. The nozzle doesn't have much to do with it.
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Offline MP99

Re: Rocket Engine Q&A
« Reply #445 on: 07/30/2012 09:09 pm »
Not over-expansion?

cheers, Martin

Offline Fequalsma

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Re: Rocket Engine Q&A
« Reply #446 on: 08/01/2012 01:37 am »
Here's a talk by Al Miller, Boeing director for  787 Technology Integration
http://www.uwtv.org/video/player.aspx?mediaid=16215102

Most of the 787 performance improvement is due to the powerplant, much more than the structures.


From a systems level too, you might be better off investing your money in improved structures to reduce vehicle inert mass (i.e. the Boeing 787's fuel efficiency is mostly due to structure).


Offline Robotbeat

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Re: Rocket Engine Q&A
« Reply #447 on: 08/03/2012 05:06 pm »
Not over-expansion?

cheers, Martin
Ah, true.
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Offline baldusi

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Re: Rocket Engine Q&A
« Reply #448 on: 10/23/2012 09:44 pm »
If the problem of using cooling on the turbo blades is that they suffer too much stress to tolerate the channels. As the size growths, does the law of surface to mass makes it possible to use channels? Or are the effect of strength non scalability bigger?

Offline Antares

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Re: Rocket Engine Q&A
« Reply #449 on: 10/24/2012 12:52 am »
Resonant frequencies in the turbopumps can also affect throttleability.

Nozzle expansion plays very little into throttleability.  You want the engine at full blast anywhere that would be a problem.
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Offline gin455res

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Re: Rocket Engine Q&A
« Reply #450 on: 11/30/2012 07:21 am »
When designing a catalyst pack for decomposing peroxide or hydrazine, is there any attention given to the aerodynamics of the flow?

For example, would a tapering, or waisted, pack act like a venturi. That is, would it reduce the pressure in the flow. Reducing pressure in a reaction thats products have more mols (and consequently more volume) than the starting reactants is an additional mechanism (additional to the catalysis on the pack surface) to drive the reaction in a forwards direction.

And, can we even assume that mixed phase flows obey the Bernoulli equation that explained the venturi effect?

Offline strangequark

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Re: Rocket Engine Q&A
« Reply #451 on: 11/30/2012 07:25 pm »
When designing a catalyst pack for decomposing peroxide or hydrazine, is there any attention given to the aerodynamics of the flow?

For example, would a tapering, or waisted, pack act like a venturi. That is, would it reduce the pressure in the flow. Reducing pressure in a reaction thats products have more mols (and consequently more volume) than the starting reactants is an additional mechanism (additional to the catalysis on the pack surface) to drive the reaction in a forwards direction.

And, can we even assume that mixed phase flows obey the Bernoulli equation that explained the venturi effect?

That's undesirable. Reduced pressure reduces the reaction rate, and increased velocity decreases the residence time. You'd have to have a much longer catalyst bed. There's also a loss of total pressure with higher flow rates.
« Last Edit: 11/30/2012 09:37 pm by strangequark »

Offline baldusi

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Re: Rocket Engine Q&A
« Reply #452 on: 11/30/2012 09:04 pm »
Why isn't oxidizer (LOX) never used to regeneratively cool the camber? It has a good deal more density to absorb the heat. Is it because it has bigger pressure losses? Because the risk of phase change?
The vortex method does use it, obviously. But has none of those issues.

Online mmeijeri

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Re: Rocket Engine Q&A
« Reply #453 on: 11/30/2012 09:08 pm »
LOX cooling has been used experimentally, and apparently it's not as dangerous as it sounds, even if there are cracks. I came across a paper describing this on NTRS once. Skylon's SABRE is also meant to use LOX cooling.
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Offline baldusi

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Re: Rocket Engine Q&A
« Reply #454 on: 11/30/2012 09:17 pm »
LOX cooling has been used experimentally, and apparently it's not as dangerous as it sounds, even if there are cracks. I came across a paper describing this on NTRS once. Skylon's SABRE is also meant to use LOX cooling.
I thought they use a He loop.

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Re: Rocket Engine Q&A
« Reply #455 on: 11/30/2012 09:25 pm »
That's for cooling the incoming air, it would use LOX for cooling the nozzle, as the LH2 is already used to cool the helium.
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Offline strangequark

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Re: Rocket Engine Q&A
« Reply #456 on: 11/30/2012 09:32 pm »
Why isn't oxidizer (LOX) never used to regeneratively cool the camber? It has a good deal more density to absorb the heat. Is it because it has bigger pressure losses? Because the risk of phase change?
The vortex method does use it, obviously. But has none of those issues.

Specific heat capacity is more important. Fuels, and LH2 especially, tend to have better specific heats. LH2 is something like 10 kJ/kg-K, whereas LOX is more like 1. So, for an engine with a 5.5 O/F ratio, the much smaller quantity of hydrogen can handle about twice the heat flux as the oxygen for the same temperature change. That, coupled with the additional aggressiveness of LOX/GOX toward your materials. Not impractical though, if there's enough benefits. Been proposed for plenty of engines, though they still tend to use the fuel first, and oxidizer as a supplement (i.e. fuel cooled combustion chamber, oxygen cooled nozzle).
« Last Edit: 11/30/2012 09:36 pm by strangequark »

Offline Danderman

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Re: Rocket Engine Q&A
« Reply #457 on: 03/01/2013 04:41 pm »
Are there many examples of engines that were designed to burn hypergolic propellants that were converted to burn cryogenic prop instead (like LOX/Kerosine)? Is there an improvement in ISP burning LOX instead of Nitric Acid or N2O4?

Offline kevin-rf

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Re: Rocket Engine Q&A
« Reply #458 on: 03/04/2013 01:02 pm »
Well, Titan went the other direction ... I believe both used variants of the LR-87/LR-91 for the first and second stages.
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Offline Danderman

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Re: Rocket Engine Q&A
« Reply #459 on: 03/11/2013 05:17 pm »
For a vehicle with a single turbopump powered engine, do some open cycle systems use the exhaust of the turbopump for roll control or steering?
 

 

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