Bio-derived Fuels for Hybrid Rocket Motors

Two bio-derived fuels have been successfully tested in a laboratory scale hybrid rocket combustion chamber located at the University of Tennessee, Knoxville. Pure lard soaked in an open cell sponge matrix and beeswax were both tested using gaseous oxygen as the oxidizer. Given similar testing conditions, these fuels exhibit higher regression rates than the common hybrid rocket propellant HTPB (hydroxyl-terminated polybutadiene), thus overcoming one of the main shortcomings of hybrid rocket fuels. These fuels also have similar or higher regression rates than paraffin-based fuels recently tested by a Stanford University/NASA Ames team. Measured thrusts ranged from 20-140 Newtons, and calculated specific impulses ranged from 60-160 seconds. All tests were excessively fuel-rich, and this leads to decreased combustion temperature and specific impulse. It is likely that this is caused by a shorter than optimal mixing chamber. This study concludes that these fuels are worth further study and could prove useful to practical application in rocketry.