ASSESSING FUEL FRAGMENTATION IN AN OXIDIZING ATMOSPHERE FOR HYBRID ROCKET PROPELLANT SAFETY COMPREHENSION

Abstract

Although hybrid rockets are considered safe, when solid fuel forms dust during impact and mixes with leaked oxidizer, a combustible gas mixture might form and burn rapidly. Therefore, to ascertain whether or not solid fuels burn by fragmentation in an oxidizing atmosphere, efforts are being made to fragment microcrystalline wax, which tends to generate dust among solid fuels under air and oxygen atmospheres. Earlier test results showed differences between results obtained in oxygen and air; however, the influence of experimental configurations cannot be ruled out. Therefore, experiments were conducted again with the air and oxygen experimental configurations combined. A transparent balloon was filled with a specimen and air or oxygen. A detonator and explosives were used to fragment the specimen. Then, the fragmentation was observed and a pressure-time history around the specimen was obtained. In all, nine experiments were conducted while varying the atmosphere, explosive mass, and presence of specimens. In all of the experiments, the pressure-time history comparisons under oxygen showed the same or higher peak overpressure and impulse compared to air. Furthermore, movies taken of experiments under an oxygen atmosphere showed strong luminescence, indicating clearly that combustion occurred in the oxygen atmosphere. The impulse values were highest in the oxygen atmosphere where the specimen was present, suggesting that the specimen burned.