[AR] Re: Paper bounty )(was RE: (mono?)propellants...)
- From: John Carmack <johnc@xxxxxxxxxx>
- To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
- Date: Mon, 3 Aug 2015 16:10:47 +0000
Thanks for that write up!
Clark’s “photosensitive” comment continues to strike me as rocketeer legend.
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On
Behalf Of Nels Anderson
Sent: Monday, August 03, 2015 6:55 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Paper bounty )(was RE: (mono?)propellants...)
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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