Environment-Friendly Composite Propellants Based on Ammonium Dinitramide

This paper gives an overview of new composite propellants with environment-friendly ingredients investigated at Fraunhofer ICT which is believed to lead to a new generation of high performance halogen-free (ammonium perchlorate free) propellants. In particular, two formulations, which can be prepared from commercially available substances, were characterized, tested and compared to the actual state-of-the-art AP/HTPB/Al in a small-scale motor campaign. The HISP project mainly focused in obtaining maximum performance, and this led to an ADN/GAP/Al propellant. It revealed stable combustion and high performance but high burning rates in the order of 24 mm/s at 7 MPa, improvable mechanical properties and some concerns about the shock sensitivity. The aim of GRAIL was to overcome these drawbacks introducing the low burning ammonium nitrate as a second oxidizer accepting some specific impulse losses. The output was an ADN/HEM/PSAN/GAP/Al propellant. The burning rate was reduced to around 9 mm/s at 7 MPa and the shock sensitivity test was passed. The mechanical properties were still poor but can be improved by coated oxidizer particles. The use of a dual-oxidizer let the pressure dependence of the Vieille's law rose till 0.6, which is borderline for a stable function of a rocket motor. Unfortunately, no ballistic modifier exist for ADN propellant up to the present day, but a lane as a high-energy metallic fuel is able to adapt ballistic properties and could be a potential propellant ingredient if commercially available.