Lotus is a first-generation liquid bipropellant rocket engine. A pair of these engines will power the Boston University Rocket Propulsion Group's Starscraper rocket to over 100 kilometers altitude. Lotus utilizes nitrous oxide and isopropanol to reach upwards of 240 seconds in specific impulse. The main objective of the design was to produce a rugged, simple, and easy-to-make engine suitable for operations within a university team.
The thrust chamber consists of three separate components: the liner, the saddle, and the sleeve. These components slide together to provide easy assembly, since no components on the entire engine are permanently affixed to each other. This allows for rapid testing and inspection, as well as parts replacement if necessary.
The liner is made from oxygen-free copper and holds the profile of the combustion chamber. 80 variable depth regenerative cooling channels are cut along the outer profile in addition to 40 film cooling orifices at the converging section of the nozzle. |
The chamber saddle profile being turned
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The sleeve is a split pair of closeouts fitted around the nozzle section to route fluid entering on the fuel inlet to the base of the cooling channels. Custom cut gaskets provide a seal along the split.
The final component is the sleeve, which is little more than an aluminum tube with fluid ports. A slight profile is turned at the base of the tube where the nozzle sits, along with a groove for a snap ring. The entire engine is inserted from the base and is retained by the snap ring. On the other end of the tube is a hole pattern for attaching the injector assembly.
The final component is the sleeve, which is little more than an aluminum tube with fluid ports. A slight profile is turned at the base of the tube where the nozzle sits, along with a groove for a snap ring. The entire engine is inserted from the base and is retained by the snap ring. On the other end of the tube is a hole pattern for attaching the injector assembly.
The cooling on the chamber was designed using custom-written tools in MATLAB. The script uses thermal resistance networks adapted for transient simulation to allow an in-depth look into how the engine behaves at each point in time. The animation to the left is an example of the output from the cooling code.
The exaggerated contour plot is useful as a first look at the transient performance, which can then be further looked into using traditional line graphs. Encouragingly, comparing the results with real data shows slight overestimation of temperatures compared to reality, which is desired since underestimation can lead to loss in hardware. |