Fragmentation Test Results For Hybrid Rocket Fuels In An Oxidizing Atmosphere

Hybrid rocket propellants are said to be safe. However, fragmenting fuel in an oxidizing atmosphere increases the risk of rapid combustion. Therefore, using a hybrid rocket propellant, tests of fuel fragmentation in oxygen were carried out as a preliminary step to the ultimate goal of conducting a dust explosion evaluation and a comprehensive safety evaluation of a whole hybrid rocket engine system. The existence of fuel and the atmosphere were used as experimental parameters to elucidate fragmented fuel combustion. The parameters were expected to generate some differences in pressure sensing and some phenomena visible by high-speed camera observation. For the tests, pressure propagation was recorded with multiple sensors. The fragmenting condition was observed using high-speed cameras. Transparent balloons were used to maintain the oxidizing atmosphere around the fuel and to observe the fragmentation with cameras. The fuel was fragmented with explosives. The fuel material and size were selected to facilitate the formation of fine fragments. Pressure waves were confirmed as blasts according to their propagation speed and time history shape. Changes in the pressure-time history were clearly affected by the atmosphere: in an oxidizing atmosphere, with or without fuel, the impulse became large. Results demonstrated that the existence of fuel little affects peak overpressure and impulse, and that it affects the blast propagation speed. High-speed videoimages confirmed that the fuel pieces were burned in the oxidizing atmosphere.