BB - Test

Test Stand

The BB test stand was made entirely of wood. The plumbing system consisted of copper tubing with brass B-nuts and it was controlled by a MatLab GUI, Arduino, and amazon solenoid valves. The stand was powered off of a 12V battery and required a 12V to 5V converter and relay. The stand fed propellants into the engine through pressurized nitrogen gas. The IPA was stored in a tank that was constructed much like the rocket engine (a thick aluminum pipe with caps bolted on the end). The test stand CAD and build are below. 

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Test Campaign

The BB engine hit several roadblocks during its testing. The main issues involved igniting the engine and producing a stable exhaust plume. The following video shows the various tests in which combustion oscillated inside and outside the engine. 

Igniting the Engine

The initial plan was to soak a cotton ball in gasoline, light it on fire, and shove it in the engine before flooding it with propellants. This proved unsuccessful since the cotton ball often clogged the nozzle and would get snuffed out during an initial pressure spike upon engine start up. Alternative solutions involved making Rocket Candy (Potassium nitrate and sugar) and molding the caramel-like mixture over two wires. These wires would then be shorted remotely, causing a spark and creating enough flame to ignite the engine. 

These igniters would frequently get blown out of the engine like the cotton ball, however, they didn't clog and burned for much longer. To secure them in place, steel wire was secured to the end of the skewer and wrapped around one of the nozzle cap bolts. This held it in long enough to ignite the engine properly. Pictured below is the stand and control table. 

Big Takeaways

Unfortunately, this project was never fully completed due to time and money constraints, but it did provide some valuable insight on a few important aspects of rocket engine design. First, our injection pressures were way too high. The chugging or pulsing of the engine was first misdiagnosed as an igniter issue, but upon looking at data and video a few months later it's obvious that the pressure drop across our orifice was way lower than what was initially expected. Second, the combustion chamber was too thin. Research on normal L* values for smaller engines isn't as easily accessible, and the lack of experience when designing this engine meant that the importance of having a proper L* was greatly underscored. A chamber with a wider diameter and shorter length should have been considered.