[AR] Re: Hypergolics with N2O?
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sat, 25 Feb 2023 02:37:29 -0500 (EST)
On Fri, 24 Feb 2023, John Lyngdal wrote:
The XLR-99 engine that powered the X-15 burned LOX and NH3 and suffered
hard start issues until they dissolved lithium in the NH3 prior to
injection.
I think I'd heard mention of this before... but I'm now a bit skeptical,
because on doing a bit of digging, several good sources make no mention of
it. There definitely was experimental work done with ammonia+lithium as a
rocket fuel, but I can't find any mention of it in connection with the
XLR-99, and moderately detailed XLR-99 flow diagrams don't show provision
for anything like that.
I don’t know if that resulted in a fuel that was hypergolic with LOX and
possibility that the effect could extend to N20.
As Ken has already mentioned, the XLR-99 had an elaborate two-stage torch
igniter (GOX/ammonia and spark plugs in the first stage, LOX/ammonia and
regen cooling in the second), so definitely not hypergolic.
The experimental work I found mention of was using WFNA or MON (mixed
oxides of nitrogen = N2O4 + NO), not LOX.
If I were to speculate, NTO and NO2 should be soluble in N20.
You might be surprised. N2O, despite having an asymmetric structure (it's
N-N-O, not N-O-N), is pretty much non-polar, as witness the way it
enthusiastically dissolves, or dissolves in, hydrocarbon fuels (usually to
the detriment of any nearby people and property soon afterward...), and
the others aren't. I don't have data on N2O4 or NO in N2O, but Clark says
N2O is not very soluble in N2O4 -- it was tried as a freezing-point
depressant, back when liquid-fuel tactical missiles were still in fashion,
without success. (NO, on the other hand, dissolves enthusiastically in
NO2/N2O4 and is very good at lowering the freezing point, which is where
the MON oxidizers came from.)
And adding NO2 or NO to your oxidizer to avoid having to deal with
pyrophoric igniter fuels strikes me as "out of the frying pan and into the
fire". :-)
Henry
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