this probably won't work at rocketry.
Injectors are standard fitting of nearly every steam locomotive. The problem is, the steam has to condense in the water to transfer the energy to pressure (speaking simply). They gain a output pressure that is higher than the input pressure of the steam. But they are known to have problems when the temperature of the feedwater is to high to condense the steam. LOX would probably evaporate inside the injector, thus no pressure would be able to build up. I have serious doubts about H2O2, too.
Michael Meinl
Ian Woollard wrote:
The pursuit dynamics pump doesn't look all that appropriate, it's a low pressure, moderate flow rate pump.
But the modern Giffard injector looks much more interesting. There's a schematic for a modern Giffard-style steam injector here:
http://www.uspto.gov/web/patents/patog/week29/OG/html/1272-4/US06595163-20030722.html
It works by putting steam through a De Laval nozzle so that it comes out slightly at or below ambient but at high speed. It wacks into some water which causes it to rapidly cool, and at the same time transfers its momentum to the water which shoots through a convergent/divergent nozzle at high speed, ending up moving more slowly but at boiler pressure. Performance is limited by the water temperature, if the injected water gets too hot it boils and then it 'breaks' (technical term, nothing explodes it just stops working until it is reset.) Original Giffard steam injectors could only manage 100 psi (they only used a convergent nozzle), modern ones (using De Lavals) achieve 80 bar or so.
So, I naturally started wondering whether you could use it for a rocket, after all, a boiler and a combustion chamber are both pressure vessels; and the Giffard injector is lighter than pumps (atleast normal pumps, I'm unclear about whether they are lighter than turbopumps).
Instead of steam tap the peroxide off the main chamber and pipe it back to the injector. If you're concerned about contaminants you could instead use a secondary water heat exchanger through the main chamber (could use it for regenerative cooling perhaps). Peroxide /probably/ won't go boom provided you keep the temperature down, it's only 10% of the propellent mass, the thermodynamics are mostly on your side (I think).
Haven't done any mass calculations, so I don't know exactly how heavy it is, but the steam bell carries about 10% of the pumped fluid, so it may not be too bad, we're looking at maybe 10% of the mass of the main combustion bell plus a bit.
Also, this same idea may work with LOX, (using a heat exchanger in the combustion chamber to produce oxygen) but LOX has a very narrow range of temperatures where it remains liquid, so I'm unsure at this point whether this works all that well, you may be limited with the maximum chamber pressure.
Normally Giffard injectors have a reputation for requiring plenty of fiddling with. It might be better with a rocket engine though; you're not fighting the chamber pressure until the fuel flow starts up; whereas a steam boiler needs to raise steam first and that causes the injector to run backwards, I'm not sure you'd have that problem; with careful design it may be self starting.
Comments?
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