[AR] Re: Alternatives to RP-1
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Thu, 26 May 2016 23:05:24 -0400 (EDT)
On Thu, 26 May 2016, Brian Feeney wrote:
Is Bio-diesel and or 100% Bio Jet Fuel an alternative to RP-1 ...
This is mainly in reference to RP-1 not plugging up cooling channels,
leaving deposits (minimum) and also relatively safe, ease of handling
qualities.
Easy and safe handling, probably pretty much. Heat stability for regen
cooling is much harder to call and I don't know that anybody really has a
definitive answer to that.
Bio-diesel has very low sulfur levels - 15 ppm or less depending on the
feed stock source and process.
Low sulfur will avoid corrosion issues, but 15 ppm isn't really *that*
low; people have seen serious corrosion issues (heavy formation of metal
sulfides) at 10 ppm with methane in simulated regen cooling.
And classical coking (cracking and polymerization), which is the problem
that RP-1 was invented to solve, is a different story and doesn't
necessarily have any relation to sulfur content. Some of the processes
used to remove sulfur impurities will tend to cure the problems that cause
coking too, but it does depend on details.
A further alternative - at engine shut down, flush at low pressure for 1
to 2 seconds using straight ethanol from a small tank employing say
helium as the pressure gas (so inert helium gas is the last element
through and left in the fuel side of the engine feed system).
Might help with some things, but I don't think it would reliably remove
classical coking products, which basically aren't very soluble in
anything.
Using straight commercial Propane as the primary fuel should also be
considered however its not as attractive in terms of handling / storage
qualities (temperature effects on density / pressure) as well as variations
in composition as has been previously discussed...
I'm told that *automotive* propane has much tighter specs than the usual
run of heating-fuel propane, and might help with that aspect. Haven't
checked on that. However, yeah, there's an issue with temperature effects
(although at the low end, propane is still liquid -- and rather denser --
at LOX temperatures).
Mind you, most any commercial propane will have "stenchant" added -- that
is, deliberately-introduced sulfur impurities -- to make leaks smellable.
Chilling it to LOX temperatures will make that stuff condense and it can
be filtered out... but then you're back to having a dangerously-flammable
gas that is heavier than air and doesn't warn you when it leaks...
Propane would seem to also fit in to the same problem zone as Methane /
LNG in terms of LOX Kaboom as is being discussed currently.
Not quite. It's not fully miscible with LOX, so it might escape the worst
of the problems. Although *some* propane will dissolve in LOX, maybe
enough to cause trouble. Hmm, a quick look through my files reveals a
posting by Roger Gregory on this list, some years ago, including:
"A stainless steel bowl add 2 cups LOX and 2 cups liquid propane (cooled
to 90K) add one lit match. The stainless steel bowl turns inside out and
looks like a hub cap that has been run over. The boom is heard by the
nearest neighbor 1/2 mile away, who comes over to inquire. And the fool
who threw in the match (not me) says his ears ring a bit."
Henry
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