My igniter orifices for fuel and GOX are 0.008 and 0.032 inches
respectively so I put 40 micron miniature filters just upstream of
them. After every test I find small bits of junk in the filters that
likely would have clogged the orifices.
-Bob
On 05/01/2016 01:44 PM, Paul Breed wrote:
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