For Stanford’s capstone Thermoscience course in Mechanical Engineering, ME 140, we were tasked with designing and manufacturing fuel grains and a nozzle for hybrid rockets fires. The ultimate goal was to maximize specific impulse while maintaining a chamber pressure of less than 1.1 MPa.

Our group decided to optimize for a linear, neutral-to-regressive burn rate with a target mixture ratio of 3. Additionally, we developed a fuel regression model to aid with fuel grain design. This allowed us to visualize how a grain would burn before a fire. Ultimately our best fire, shown to the right, yielded a specific impulse of 174.6 s, good enough for second in the class. Furthermore, this fire yielded a mixture ratio of 4 and a chamber pressure of .99 MPa. For more in depth discussion of analysis and results, see the report linked below.

Note that the nozzle was machined out of graphite on a manual lathe, and the fuel grains were machined out of HDPE on a manual lathe and mill. Both were governed by strict dimensional tolerances. Ultimately, we machined and tested 5 different fuel grain designs with a single nozzle.