2001-08-27

Finally finished the machining of the rocket motor! I don't have a digital camera yet so there's no pictures as of now. But, the parts look really cool! Now, I need to start building up test fixtures, etc. Started the design of the test fixture. The propellant tanks will be pressurized from a helium tank, controlled by an electric valve. The propellant tank valves will be ball valves controlled by a pair of air actuators which in turn are controlled by an electric valve. The propellant tanks will be 4 inch diameter x 0.25 wall 6061 aluminum tubing welded to a pair of aluminum end plates.

2001-06-25

Finished drawings for the latest injector body. Since C1018 steel is totally unsuitable for LOX service, I'll be using 304 stainless steel for the injector assembly. I'd still like to use C1018 steel for the combustion chamber as it is somewhat easier to machine than the stainless steel.

I got some samples of Grafoil (flexible graphite) that I'll use to make a gasket between the combustion chamber and injector. This stuff is really cool. It has a sublimation point of 6000 deg. F (it never melts). The best part is it cuts just like thick paper.

I think I finally have all the shop supplies I need to start fabrication so stay tuned for more progress reports.

Coming up: strength-of-materials calculations for the chamber (fasteners, wall thickness, etc.), ideas for the regeneratively cooled chamber.

2001-05-23

I came up with a design for the injector assembly that doesn't have any joints or seams for the LOX path. The fuel manifold has an annular ring that feeds the injector holes.

2001-04

Here are the specs I'm looking at for the uncooled engine:

Fuel:                Kerosene
Oxidizer:            Liquid Oxygen (LOX)
Mixture ratio:       1.8 (2.24 is ideal but 1.8 reduces the combustion temp.)
Thrust:              100 lbf
Chamber pressure:    200 psia
Chamber diameter:    2.24 inches
Chamber length:      4.0  inches
Nozzle throat dia.:  0.71 inches
Nozzle exit dia.:    1.23 inches
Injector pairs:      4
Fuel injection dia.: 0.045 inches
Oxidizer inj. dia.:  0.051 inches
Chamber temperature: 5400 Deg R (4940 Deg F)
Specific Impulse:    225 sec

The combustion chamber will be be machined from a solid 3 inch diameter, C1018 steel bar. I'd love to figure out a better way to fabricate this and still keep good tolerances.

The propellant tanks will be pressurized by Helium gas.

This test chamber is considered "uncooled", i.e. non-regenerative but to increase run times, it will be cooled by a few streams of water. I'm hoping to get at least 5-10 seconds of run time out of it before it melts. The next version will have internal cooling passages where the fuel will circulate to keep the chamber and nozzle walls at a reasonable temperature. The purpose of building and testing the uncooled version first is to get some of the basic issues out of the way such as:

  • Ignition and starting
  • Combustion stability (may require injector changes)
  • LOX handling, transportation
  • Data/video system setup and operation
  • Machining techniques
  • Test stand checkout
  • High-pressure Helium system checkout