Student investigation of rapid prototyping technology for hybrid rocket motor fuel grains

This study reports on a class project designed to introduce students to applications of additive manufacturing in the rocket propulsion industry. Students from the Mechanical Engineering department at Alfred University (AU) have designed, built, and tested small-scale hybrid rocket motors. The project focused on design and fabrication of a test rig that could test many different grain geometries. The students used CAD and CAM software to design this hardware, and had the opportunity to work with a CNC mill and lathe to machine their designs. The primary additive manufacturing technology investigated in this project was 3D printing and was used to make unique hybrid grain designs. The novel ABS hybrid grains were made with additive manufacturing technology from two very different machines, one much more advanced than the other. Through small-scale propulsion testing at AU, we developed a reliable test to compare grains made with the inexpensive printer. To validate our testing and introduce students to a more advanced propulsion test lab, we tested several 3D printed grains at The Pennsylvania State University's High Pressure Combustion Lab (HPCL). This project was coupled to a senior-level fluid mechanics course taught at AU, and students were introduced to nozzle sizing and simple hybrid rocket motor ballistic predictions and analysis. Difficulties in accurately predicting the performance of complex grain geometry was introduced as well by comparing to data from the various tests. The ultimate goal of this student-led research is to report on the future impact additive manufacturing technology could have on hybrid rocket performance, with suggestions for grain designs.