Talk:SABRE
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Ok, this piece seems to me to be difficult to write, it's a fairly complex engine, and the information probably isn't complete. But we do the best we can.
I've made some corrections to the piece which I believe are correct. They include:
a) the helium loop is gaseous, not liquid (see section 4.1 JBIS_v57_22-32.pdf)
b) the air isn't separated into nitrogen and oxygen anymore with Sabre, unlike LACE
c) the helium loop isn't pumped, on the contrary it does the pumping ("Brayton cycle"). Check out the diagram 4 and the discussion in section 4.1 in the above document
There's still some stuff I don't know for sure:
I'm still not clear whether SABRE actually liquifies the air- I've a feeling that it only cools and compresses it; but I haven't seen anything written in black and white either way. Liquifying it would probably be a bad idea, since it uses more hydrogen and doesn't actually improve the efficiency. I noticed that the experimental precooler only cools the air down to -80C; AFAIK it's not written in black and white anywhere whether that's the same temperature that they would employ on SABRE, but if so, then that's far too warm to liquify the air.
If anyone knows of a reference we can point to, I'd appreciate it.
Incidentally, it might be a good idea for someone to ask Bond and co. whether we could include their engine diagram and an external view of the engine here- a diagram or two would be very desirable.
-WolfKeeper
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The only reference I can find on the liquifaction/cooling the air issue is section 4.1, where they talk about an air compressor after the precooler. Given that liquid air is incompressible; this implies that the output from the precooler is gaseous.
-WolfKeeper
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Actually, there's another, rather clearer description of why SABRE does *not* liquify the air in JBIS_v56_108-117.pdf, page 115.
Given this, I'm going to change the article to remove reference to liquid air with SABRE.
-WolfKeeper.
[edit] Looking very good now
Thanks for the heads up WolfKeeper. I have read the articles in question and I think the article really reflects the actual system much better now.
I do find it interesting that dragging around "dead" engines for much of the flight profile still results in massively better performance overall. But I suppose that should not be expected, after all, we have reheat/afterburners.
Maury 22:21, 13 July 2005 (UTC)
just one comment -80°c may liquify air at high pressure, at Mach 5,and 60,000ft 20,000m the stagnation pressure should be about 31.7 bar stagnation temperature 1335 k (isentropic compresion), liquifyed air (any liquid) is easier to pump up to a high pressure (as they are incompresable), and high presures are important for cycle efichiencies. the problem with liquifying air however is that not all the gasses will condence at the same temperature, and much erosion can be expected if the liquid droplets are traveling at any speed in the heat exchanger. incidently the loss of entropy for such heat exchangers are probably horrific.
