Solid fuels for ramjets and hybrid rockets

For missiles such as air-to-air missiles, solid fuel ramjets are of particular interest. This type of engine is in principle identical to a hybrid rocket engine, but with the difference that the latter require carrying the oxidizer required for combustion. For these types of propulsion systems , hexamine has previously been identified at FOI as a promising filler to be used in HTPB based solid fuels. Many of the problems encountered when developing this type of fuels have been solved and the density of HTPB-based fuels could be increased by 30% by adding hexamine. The purpose of the work reported here was to improve the mechanical properties of the fuel and to scale up the batch sizes. In the formulation work a number of different parameters have been altered and two potential bonding agents were evaluated. However, the mechanical properties varied substantially between the different batches made, making it hard to draw any definite conclusions. At best, mechanical properties similar to conventional composite propellants were obtained, but the results have currently not been possible to reproduce.