I built some 250 lb LOX/Ethanol Lox centered regen pintile motors.
These had copper liners and aluminum outers... I you read my blog from
about 2007 you will find much commentary. (unreaosnable rocket)
You can see one running 113 seconds here:
https://www.youtube.com/watch?v=GryfvPoRN5Q
Getting the pintile gap right was hard.
You must turn both the alignment surface and the pintile gap in the same
setup. This means you must be able to accurately measure the small inside
diameters while you are machining. I purchased a whole set of precision
ground test pins in the sizes of interest. Theses were in 0.001
increments...
If you make the fuel 75% ethanol and 25% water it has almost no effect on
ISP (try it in cpropep or whatever your using) but has a huge impact on
cooling. It will effect your nominal mixture ratio.
I also had issues with making the igniter hot enough to light the motor and
not so hot that it melted the chamber wall before it lit.
Garvey has had good luck using a small ap solid rocket motor as an igniter
for his liquids. If I was doing a liquid that required an igniter now I'd
probably go that route. The igniters on the 250 lb motors had such small
orfices that keeping them fod free was impossible.
I'd vote for aluminum chambers for the better cooling.
I might also have the throat flame sprayed with zerconinum. (sp?)
I have not flame sprayed my current batch of 3D printed AL motors, but I'm
running at reallly low pressures (200psi)
Paul
On Sun, May 1, 2016 at 9:55 AM, John Dom <johndom@xxxxxxxxx> wrote:
I suppose 3D printing uses one of the inconel powders containing 30 %
nickel to be wary of. Yikes that could give you nickel allergy or worse. Or?
jd
-----Original Message-----
From: Kristin Travis
Sent: Apr 30, 2016 11:34 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