Thank you all for the great advice and comments. I apologize for the slow
reply, you know.....engineering school :)
We are currently working on an aluminum chamber design and changing the
pintle to LOX centered. I will post updates as soon as the drawings are
complete. I'm sure will have more questions as well.
Thanks again!
Kristin and the PSAS Liquid Fuel Capstone Team
On Mon, May 2, 2016 at 10:08 PM, FreeLists Mailing List Manager <
ecartis@xxxxxxxxxxxxx> wrote:
arocket Digest Mon, 02 May 2016 Volume: 04 Issue: 105
In This Issue:
[AR] Re: Portland State Aerospace Liquid Fuel Rocket Engine
[AR] Re: aluminum (was Re: Portland State Aerospace Liquid
F
[AR] Dry vs. wet lubrication for LOX
[AR] Re: Dry vs. wet lubrication for LOX
----------------------------------------------------------------------
From: "Carl Tedesco" <ctedesco@xxxxxxxxxxxxxx>
Subject: [AR] Re: Portland State Aerospace Liquid Fuel Rocket Engine
Date: Mon, 2 May 2016 13:48:51 -0700
Regarding 0.008” annular LOX clearance on the pintle…
As mentioned that needs to be controlled via tight tolerancing. I think
you would need to post machine some alignment features. Even a precision
cylindrical boss into a precision reamed hole will have some tolerances
(+/-.0005 ???). I wonder if a tapered boss and tapered hole would be better
for alignment. Thoughts?
Carl Tedesco
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx]
On Behalf Of Kristin Travis
Sent: Saturday, April 30, 2016 8:35 PM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Portland State Aerospace Liquid Fuel Rocket Engine
Hello All,
My senior mechanical engineering capstone team is designing a 250 lb
thrust liquid fuel engine for the Portland State Aerospace Society. This is
our first time posting on arocket. We are working with Kyle Meeuwsen who
has posted about designing the test stand.
Our plan is to 3D print the engine in metal so we can print regenerative
cooling channels in the nozzle and chamber walls. We are planning on using
a pintle injector and ethanol/liquid oxygen propellants. We have been told
we can print to a resolution of 0.03 for steels and 0.015 for aluminum.
Here is the link to our engine design document:
https://github.com/psas/liquid-engine-capstone-2015/blob/master/PSAS_Design_Review1.pdf
1. This design assumes we are printing in inconel, which results in very
thin chamber walls due to heat transfer properties of the metal. We are
wondering what people think about printing it in aluminum in order to have
thicker walls and larger cooling channels.
2. For the pintle injector we have been getting some mixed feedback on
whether we should have a fuel centered (fuel inside the pintle) or LOX
centered design. The plumbing gets much simpler with a LOX centered design,
but most of our research on small engines indicated fuel centered designs
are better because they spray the chamber walls with fuel instead of
oxidizer.
3. We are also looking for recommendations for connectors to the test
stand plumbing (not shown in our drawing). We can 3D print bosses and cut
threads or we can 3D print some type of male connectors.
4. We are thinking of machining the pintle injector out of stainless steel
and using EDM (electric discharge machining) to create the holes. We are
wondering about material compatibility issues (such as thermal expansion)
between the 3D print metal and a stainless steel pintle.
We are documenting our design calculations in Jupyter notebooks. They are
still a work in progress, but they can be viewed here:
https://github.com/psas/liquid-engine-capstone-2015/blob/master/Pintle%20Injector.ipynb
https://github.com/psas/liquid-engine-capstone-2015/blob/master/Nozzle_Construction/LFRE.ipynb
Any feedback would be greatly appreciated.
Thank you,
Kristin Travis
------------------------------
Date: Mon, 2 May 2016 15:26:00 -0600
Subject: [AR] Re: aluminum (was Re: Portland State Aerospace Liquid Fuel
From: Jonathan Goff <jongoff@xxxxxxxxx>
Henry, Gerald, et al,
There's a local company that does custom metal, ceramic, and MMC powders
for eos DMLS 3d printers that has a really interesting aluminum MMC (I
think with TiN and TiB2 reinforcement) they're working on. Think of it sort
of like a Glidcop for aluminum. You keep most of the thermalconductivity of
native aluminum (~200W/m*K), but it gets decently high tensile strength (a
little higher than 6061 aluminums), and its softening temperature is much
higher. IIRC it still has >30-40ksi tensile strength at 600F.
But even regular aluminum is pretty interesting if done right.
~Jon
On Sun, May 1, 2016 at 2:58 PM, Ian Woollard <ian.woollard@xxxxxxxxx>
wrote:
Aluminium alloys certainly work (i.e. professionals have flown them inbetter
space), and they can have very good high thermal conductivites, and they
are pretty lightweight. However the temperatures that the alloys start to
misbehave at are really rather low (~150C), and they are really rather
prone to warping and ageing.
Overall, the modelling I've done suggests they work reasonably well at
relatively modest chamber pressures like around 10 bar, but above that
other copper and nickel and even steel based materials seem to have
properties for handling the higher pressures and hence high thermalfluxes
and that can allow for longer, more efficient nozzles/higher Isp, withfar
less chance of significant metallurgical issues.not
On 1 May 2016 at 18:11, Henry Spencer <hspencer@xxxxxxxxxxxxx> wrote:
On Sun, 1 May 2016, Gerald Taylor wrote:
Aluminum has a low melting temperature, a rather low softening
temperature where it loses its temper, low strength and stiffness when
withintempered...
While all of that is true, it's largely counterbalanced by the fact that
aluminum has *very* high thermal conductivity, so it's hard to get local
overheating in a regeneratively-cooled engine. Last I heard, Masten's
flight engines (hundreds of flights, heaven knows how many ground tests)
are all aluminum, and they're not the only folks doing it.
This is also a large part of why Columbia's wing lasted as long as it
did. Despite the severity of the hot-gas leak, the hydraulic systems
going isthe wing failed before the aluminum structure did.
and if the aluminum oxide surface cracks, would make one heck of a fuel.
Aluminum-oxide cracks generally are self-healing because new oxide forms
instantly on the newly-exposed surface. In practice, aluminum generally
won't ignite until well above its melting point. It's a ferocious fuel
when it gets going, as witness its use in thermite, but getting it
excellenttough, as witness the drastic measures needed to ignite thermite.
(Many high-temperature metals are much more vulnerable to such things,
because they don't form oxide layers or their oxides aren't such
oneprotection, so they need deliberately-added protective coatings, and if
of those cracks, watch out.)
Henry
--
-Ian Woollard
Sent from my Turing machine
------------------------------
From: Robert Watzlavick <rocket@xxxxxxxxxxxxxx>
Subject: [AR] Dry vs. wet lubrication for LOX
Date: Mon, 2 May 2016 21:15:38 -0500
I'm preparing for some more cold / LN2 tests of my semi-custom ball
valves. I was reading Bal Seal TR-75 (Shaft and housing materials,
coatings, and lubricants for optimal cryogenic sealing) and it says:
"Wet lubricants may be used at temperatures to –77 F (–60 C). At lower
temperatures, dry lubricant should be used. Dry lubricants are
recommended for cryogenic service because they improve seal performance
and create a protective film between the seal and sealing surface. The
protective film reduces friction and seal wear, minimizes galling, and
improves sealing ability."
For dry lubricants, it recommends:
Microseal (Metal Improvement Co.)
Molydisulfide Spray Coating (Anadite, Inc.)
Graphite Spray-On Coating (Crest Coating, Inc. ) - is graphite oxygen
compatible?
I need some lubrication to assemble the spring loaded stem seal but I've
always used Krytox (actually I use Tribolube-16 because it's cheaper).
Now I'm wondering if the grease makes the problem worse by turning rock
hard and keeping the seal from staying formed around the shaft. I was
considering Dow Molykote Z because it is readily available.
Anybody have experience on the best lubricant for a cryogenic shaft seal?
-Bob
------------------------------
Subject: [AR] Re: Dry vs. wet lubrication for LOX
From: Henry Vanderbilt <hvanderbilt@xxxxxxxxxxxxxx>
Date: Mon, 2 May 2016 21:11:30 -0700
I can testify that Krytox oil freezes to rock a long, long way before
you reach liquid nitrogen temperatures. Something under -60C sounds
about right, but I don't recall exact numbers. (I'd assume the same
about Krytox grease, but I don't know that from personal experience.)
I very much would not assume any graphite-based lube is LOX-compatible.
The others, I have no idea.
Henry
On 5/2/2016 7:15 PM, Robert Watzlavick wrote:
I'm preparing for some more cold / LN2 tests of my semi-custom ball
valves. I was reading Bal Seal TR-75 (Shaft and housing materials,
coatings, and lubricants for optimal cryogenic sealing) and it says:
"Wet lubricants may be used at temperatures to –77 F (–60 C). At lower
temperatures, dry lubricant should be used. Dry lubricants are
recommended for cryogenic service because they improve seal performance
and create a protective film between the seal and sealing surface. The
protective film reduces friction and seal wear, minimizes galling, and
improves sealing ability."
For dry lubricants, it recommends:
Microseal (Metal Improvement Co.)
Molydisulfide Spray Coating (Anadite, Inc.)
Graphite Spray-On Coating (Crest Coating, Inc. ) - is graphite oxygen
compatible?
I need some lubrication to assemble the spring loaded stem seal but I've
always used Krytox (actually I use Tribolube-16 because it's cheaper).
Now I'm wondering if the grease makes the problem worse by turning rock
hard and keeping the seal from staying formed around the shaft. I was
considering Dow Molykote Z because it is readily available.
Anybody have experience on the best lubricant for a cryogenic shaft seal?
-Bob
------------------------------
End of arocket Digest V4 #105
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