Thanks Nels, that is an interesting write up. The LOX/LCH4 monoprop is
actually quite a bit more stable than I anticipated, though clearly
something to be worked on remotely if you are feeling ambitious enough to
work on it at all.
Lloyd
On Mon, Aug 3, 2015 at 11:55 PM, Nels Anderson <nels.anderson@xxxxxxx>
wrote:
On 06/23/2015 02:11 AM, Lloyd Droppers wrote:
John,on high energy propellants, and number (03) has the following summery
NTRS has some versions of SP-7002, effectively a bibliography of papers
/* quoteMETHANE MIXTURES. James 0. Thieme and Richard L. Every (Continental Oil
IGNITION AND COMBUSTION CHARACTERISTICS OF LIQUID OXYGEN AND LIQUID
Co., Ponca City. Okla. 1. (American lnstltute of Chemlcal Engineers.
National Meeting. 56th. San Franclsco, Calif.. May 16-19, 1965, Preprmt
28e.) Chemical Engineering Progress, Symposium Serles. no. 61, 1966. p.
113-117.
This paper presents the results of a study necessary to evaluate thepossibility of using liquid oxygen liquid methane mixture as rocket
monopropellants. The experiments were designed to determine the ignition
and controlled burning feasibility of these fuel and oxidizer mixtures.
Results of these tests show that liquid oxygen liquid methane mixtures can
be burned under certain conditions. These conditions are presented as well
as less favorable conditions where detonation can be expected to occur.
damage incurred from an unexpected detonation are also included.
Photographs of the damage incurred from an unexpected detonation are also
included. (Author)
*end quote */*
I dropped by my local reference library and read Thieme's and Every's 1966
paper.
Their interest in lox-methane monoprops was driven not by plumbing
simplicity but by the hope that the well-mixed propellant would offer
higher Isp than a conventional biprop. Their experiments literally began
and ended with a bang. In between, the had a number of quiescent runs up
to about 6 seconds' duration with a few different set-ups. Details follow.
Firstly they put lox and liquid methane in a beaker and lit it. Kaboom:
"it was apparent that future tests would have to be carried out with
extreme caution."
Then they built two 250-mL Lucite tanks, one for liquid methane and one
for liquid oxygen, both pressurized to 50 psig with gaseous nitrogen from a
common source. 1/8" stainless-steel tubing led from each tank through a
manually-operated stainless valve to a T-coupling with a 1/8" exhaust tube.
In the first runs, only the methane tank was filled. The liquid squirting
out the exhaust was lit, resulting in a bright red-orange (fuel-rich) flame
beginning 2-3" from the tube.
For the next set, both tanks were filled. The methane valve was opened,
the stream ignited, and then the oxygen valve was opened. This produced a
smaller and hotter yellow-orange flame, presumably still fuel-rich. The
burn lasted "a few seconds."
The next step was to mix measured amounts of methane and oxygen in a
500-mL stainless tank. The tank contained a copper cooling coil through
which liquid nitrogen circulated as the propellants were fed in, methane
first, in gaseous form, and liquefied. Discharge was through a 1/8"
stainless tube controlled by a manually-operated 1/4" valve. "After
condensation, the liquid mixture was pressured with 40 to 65 lb./sq. in.
dry nitrogen, the valve on the discharge tube was opened, and the mixture
ignited by remote control. A similar run was made except that the mixture
was pressured with oxygen-methane vapor. Tests were made with both
fuel-rich and oxygen-rich mixtures with over pressures varying from 40 to
60 lb./sq. in." At a molar mixture ratio of 3:1 (i.e., stoichiometric), a
hot blue-white flame resulted. The lox-methane "mixture could have been
burning inside the discharge tube, but no further than 2 in. since closing
the valve always extinguished the flame."
Finally, the manually-operated discharge valve was replaced by a solenoid
with a 1/8" orifice, and the the 1/8" discharge tube was replaced by a 1/4"
tube with a 3/16" orifice. Two tests, lasting about 3 seconds each, were
run with a total of 125 mL of propellants (ratio not specified -- I'd guess
stoichiometric). Then the propellant load was increased to 250 mL,
resulting in a burn of about twice the duration.
The last test also made use of 250 mL of propellant. "The camera
equipment was placed in position, since all previous test results had
indicated the mixture could be burned safely. After all of the preliminary
preparations had been made, the solenoid valve was actuated. The instant
electrical contact was made, the sample detonated. The cause of the
detonation is unknown; however, the flame front definitely migrated
backward through the 1/8" solenoid orifice. One possible explanation of
the detonation would be that the overhead pressure line condensed moisture
and then froze, preventing nitrogen gas from entering the fuel tank."
Thieme & Every conclude: "This research program has definitely illustrated
that liquid oxygen-liquid methane mixtures can, under the proper
conditions, be burned with complete control. The overhead pressure and the
discharge orifice size are believed to be the critical parameters involved
in the ignition and burning behavior of the mixtures. Although this study
leaves many questions unanswered, it is useful as a basis for a more
extensive and sophisticated research effort."
All in all, I'd say Thiem's & Every's conclusion that lox-methane monoprop
can "definitely" be burned safely is a little shakey, given that they don't
know what caused the explosion. They have less reason to be confident of
lox-methane's safety than Scaled had for nitrous. On the other hand, a
little more work might explain the explosion (by the way, I could find no
references in later literature to this paper).
Among the three sources cited is British patent (to download, go to
worldwide.espacenet.com do a "smart search" for gb855200) for a
lox-methane explosive. That might not sound a promising basis for a
monoprop, but the patent goes to some length as to preventing unintended
explosions. From a quick read, the key is keeping the right vapor
pressures of oxygen and methane and not letting solid methane precipitate.
Of course, preventing explosion of a stored monoprop isn't the same as
preventing a burning one from exploding.