Cool project! Yes, regarding plumbing it makes sense to feed the
propellant component which is used to cool the chamber walls through the
annular gap. I did that for a N2O/Ethanol engine. In that case the N2O
was the coolant because of the higher mass fraction available to cool
the chamber. It doesn't make sense for LOX though. Personally I would
stick with the LOX centered approach, but maybe I am wrong.
2 cents:
- At this small scale, a precise centering of the pintle is crucial. A
simple thread is not enough to ensure a proper centering.
- The engine has a quite huge surface exposed to the combustion gases
compared to the available coolant (which is a general problem of small
engines). What is the temperature of the coolant when it leaves the
cooling channels? Is it really below the boiling point at the
corresponding pressure? Are you really below the local critical heat
flux density?
About point 4:
Personally I would make a removable pintle tip. So you could make your
injector holes with wire EDM or even classical on a mill. Make your
pintle as modular as possible (that's why I love the pintle approach,
it's so easy to change the settings)
Cheers Bruno
Am 01.05.2016 um 05:34 schrieb Kristin Travis:
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