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#20
by
acsawdey
on 16 Apr, 2015 16:25
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As another data point, a PT6A-65 turboshaft has a dry weight of 220kg and shaft output around 1MW. But you'll need to add a generator to that, at which point the ~300kg of Li-poly batteries starts to look pretty competitive and a whole lot cheaper. Also that's going to consume some of your RP-1 and so impacts both dry weight and Isp.
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#21
by
ArbitraryConstant
on 16 Apr, 2015 18:49
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With the electric pump, you could do a trade and make it partially pressure fed.
All LREs do this to an extent. Even just the hydrostatic pressure is probably >1atm on Electron for the LOX when fully loaded.
As another data point, a PT6A-65 turboshaft has a dry weight of 220kg and shaft output around 1MW. But you'll need to add a generator to that, at which point the ~300kg of Li-poly batteries starts to look pretty competitive and a whole lot cheaper. Also that's going to consume some of your RP-1 and so impacts both dry weight and Isp.
And more turbomachinery they have to develop.
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#22
by
QuantumG
on 17 Apr, 2015 08:55
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What kind of pumps would you use for electric drive?
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#23
by
gin455res
on 17 Apr, 2015 10:00
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I wonder whether using these instead of pressure-feed in previously pressure-fed hypergolic systems would make a useful difference to performance (thinking improved mass fraction).
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#24
by
gin455res
on 17 Apr, 2015 10:07
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327 ISP is that sea level or vacuum? Either way that about splits the isp of the RD-180 if its vacuum, if that's sea level then it exceeds it. Basically stage combustion level ISP without having to deal with stage combustion. Pretty impressive.
...
Basically these performance characteristics are what make me think of this as an alternative to pressure fed and expander, rather than large gas generators and staged combustion. It's simple and cheap like pressure fed, with the ISP of an expander, quite a large mass penalty but I suspect not the end of the world compared to pressure fed (since compressed gas has lower specific energy than battery) and MUCH simpler and more freedom in propellant choice than expander (is kerolox expander even possible?).
....
I've sometimes wondered what is wrong the idea of having a 'tripropellant' kerolox rocket driven by an open-cycle hydrogen expander pump. (sorry off-topic)
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#25
by
gin455res
on 17 Apr, 2015 10:20
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Could this be used to pump fuel into the combustion-chamber of an oxidizer-rich staged combustion engine?
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#26
by
Asteroza
on 17 Apr, 2015 11:04
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What kind of pumps would you use for electric drive?
Is the question as to types such as centrifugal, axial, and/or reciprocating pumps, for example? Motor characteristics may play a factor, such as high RPM, torque profile, matching to power source, AC/DC/polyphase, etc.
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#27
by
Nilof
on 17 Apr, 2015 11:30
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I've sometimes wondered what is wrong the idea of having a 'tripropellant' kerolox rocket driven by an open-cycle hydrogen expander pump. (sorry off-topic)
You mean like the RD-701 in kerolox mode, where kerosene is the primary fuel but hydrogen still fuels the turbopump? You can get some wicked chamber pressures and Isp with that. The RD-701 in kerolox mode had a 30 MPA chamber pressure and a 330s
sea level Isp on a vaccum optimized engine. The vaccum isp was 415 s.
Somewhat off topic in this thread though.
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#28
by
ArbitraryConstant
on 17 Apr, 2015 15:10
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Could this be used to pump fuel into the combustion-chamber of an oxidizer-rich staged combustion engine?
My intuition is that the high pressure gradient on SC would take too much power and enough battery that it wouldn't make sense. If you have staged combustion you have turbines powered by the preburner for pumping.
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#29
by
QuantumG
on 18 Apr, 2015 07:35
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Ever since I heard of the concept I've always thought that electric pumps were a safer concept for amateurs building their first liquid rocket. Instead of having to build a heavy tank that can stand the pressures of blow-down and the risks of an exploding tank, you can use lightweight tanks and a commercially available pump running from mains power. I think amateurs often reject the idea because they don't think they'll be able to make a flight-weight pump-fed engine, and conclude they're going to need to master the skill of making high pressure talks anyway.
Even if your goal is to fly a pressure-fed vehicle, I think you can learn a lot about making rocket engines by starting an electric pump test stand. Of course, the big problem with this theory is that I've not found any such pump off-the-shelf which doesn't cost a fortune.
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#30
by
john smith 19
on 20 Apr, 2015 07:33
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What kind of pumps would you use for electric drive?
Is the question as to types such as centrifugal, axial, and/or reciprocating pumps, for example? Motor characteristics may play a factor, such as high RPM, torque profile, matching to power source, AC/DC/polyphase, etc.
Good point.
John Whiteheads group at Livermore reckoned reciprocating positive displacement pumps (originally designed to replace pressure fed liquid systems) were better up to 5000 lb thrust.
Historically the bulk of US turbo pump systems have been centrifugal, with axial flow reserved for LH2.
Note there is no real reason for this beyond a)Von Brauns team built the V2 using pump designs derived from fire engine water pumps because they were worried about pressure pulses triggering combustion instability effects b)that's how Rocketdyne did it and as they were the US leaders in rocket engine production everyone played follow-the-leader.
Russian work went with radial inflow systems, which IIRC are actually a few percent more efficient, but a bit more difficult to design. OTOH they are somewhat easier to make once the design has been done.
In the US Barber Nicholls seem to be the leaders in this type of design and were (are ?) involved in the Merlin pump design for SX.
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#31
by
sanman
on 22 Apr, 2015 08:19
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#32
by
gin455res
on 22 Apr, 2015 12:47
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Any idea if it would be easier to 'play lego' with electro-pumps?
Kinda like the idea of a Falcon 5 1/3 with a penta-web of gas generator engines surrounding a small 1/3 thrust central electro-pump engine for improved throttle response when landing.
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#33
by
john smith 19
on 22 Apr, 2015 13:46
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Does anyone remember a discovery called "Thermopower Wave"? The extremely high power demand of an electric turbopump sounds like a good fit for it:
No but if you read the first article they'd got to a 0.1% conversion efficiency, although that seems to be up from 0.000001% they started with.
This looks like something like thermionic generation (heat into direct free electron motion) and a "thermal battery" like the kind used by various weapon systems.
BTW Thermal batteries don't store heat. They are so called because they need heat to melt the (very) solid electrolyte of a primary cell and get the reaction started. Thermal batteries have "ignition sequences" to fire the incendiary mix that gets the battery working. This means they don't self discharge, giving
very long shelf lives, at the expense of a) expense (built to the design of hardware they are powering with lead times to match) and b)a delay while they warm up.
I'd guess this tech will have similar issues, along with being about 1/1000 as efficient at present.
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#34
by
JasonAW3
on 22 Apr, 2015 13:47
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Out of curiosity; Anyone know how electromagneticly interactive cryogenically cooled fuels are? Like LOX and Liquid Hydrogen?
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#35
by
gary hedman
on 22 Apr, 2015 14:40
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Since you don't need to recharge, a lithium sodium battery with twice the energy denisty at present levels of development seems applicable.
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#36
by
MP99
on 22 Apr, 2015 20:32
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Could this be used to pump fuel into the combustion-chamber of an oxidizer-rich staged combustion engine?
Staged combustion is a way to burn some of the prop to run a turbopump.
Doesn't seem to be applicable to an electric pump engine.
Cheers, Martin
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#37
by
gin455res
on 22 Apr, 2015 20:48
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Could this be used to pump fuel into the combustion-chamber of an oxidizer-rich staged combustion engine?
Staged combustion is a way to burn some of the prop to run a turbopump.
Doesn't seem to be applicable to an electric pump engine.
Cheers, Martin
I meant using the turbopump to pump the oxygen (large volume) and the electric pump to pump the fuel (small volume assuming HC fuel) perhaps one small electric pump for the pre-burner and a bigger one for the main combustion chamber. thought it might simplify system design, while maintaining some of the power to weight of staged combustion.
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#38
by
Nilof
on 22 Apr, 2015 20:55
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Well, looking at a "typical" SC engine such as the shuttle, it has both low pressure and high pressure turbopumps. Maybe you could have a system where the low pressure pumps that are mostly there to pump the fuel could be electric, while the high pressure pumps that are for compression/cycle efficiency could be turbine driven?
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#39
by
Port
on 22 Apr, 2015 21:08
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Since you don't need to recharge, a lithium sodium battery with twice the energy denisty at present levels of development seems applicable.
exactly my thought, also Li (or Zn, Al)/Air (LOX?) come to mind
