In order for our preferred combustion theory to happen correctly, we designed the injector to shoot multiple iterations of two miniature jets at one other. When the jets collide a few millimeters into the body of the engine, the liquid spreads out into a “droplet fan,” making it easier for the fuel and oxidizer to mix. (And ultimately, burn.)
The CAD was designed, the part was printed — all that remained was to verify it worked. So, three members of Castle Point Rocketry’s mechanical engineering team stayed up into the wee hours of Thursday morning to test our injector.
A five-gallon water jug, some flexible tubing, and one high-speed camera later, the team had a pretty good idea that our brain child was a go. The test differed from final implementation in five keys ways, but the fact that it didn’t — well, explode — is a good sign.
(1) The test was run on an 85% scale model printed on campus at Stevens’s PROOF Lab. (2) Our final injector will be solid metal but the test part was made of plastic shells. (3) We ran a lower operating pressure and fluid flow rate than the real part will encounter. (4) The part was not meticulously deburred before testing. Little shards of print plastic could have been partially obscuring the outlet orifices. (5) Water was used as our test fluid but the rocket will burn jet fuel in pure oxygen.
Over the course of the day (and night), six runs were performed over a range of water pressures. The first two, performed in a lab sink, were a public spectacle for the whole team. Monica, our resident injector design chemical engineer, spent most of that time with her head in the sink watching the impingement for defects.
Our next steps: Print a new model and find a test liquid with properties closer to that of jet fuel.
You can find a nice slow-motion video on our Facebook page (http://www.facebook.com/CPRocketry/).