[AR] Re: Paper bounty )(was RE: (mono?)propellants...)
- From: Nels Anderson <nels.anderson@xxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Mon, 03 Aug 2015 12:55:24 +0100
On 06/23/2015 02:11 AM, Lloyd Droppers wrote:
John,
NTRS has some versions of SP-7002, effectively a bibliography of
papers on high energy propellants, and number (03) has the following summery
/* quote
IGNITION AND COMBUSTION CHARACTERISTICS OF LIQUID OXYGEN AND LIQUID
METHANE MIXTURES. James 0. Thieme and Richard L. Every (Continental Oil
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 the
possibility 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.
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