Combustion Behavior of Aluminum Particles in ADN/GAP Composite Propellants

Propellants containing ADN/GAP are regarded as a promising green alternative to AP/HTPB solid rocket propellants because of avoiding chloric acid emission. The addition of aluminum powder is a classical approach to increase the theoretical specific impulse of composite propellants. The optimum aluminum content is in the range of 16-18 % Al. But propellant formulations with ADN, a chlorine-free oxidizer, and GAP, an energetic binder, generate no chloric acid but more nitrogen on combustion achieving similar performance. Significantly different thermal and chemical conditions occur to the aluminum particles close to the burning surface. This study investigates the combustion behavior of aluminum particles in an ADN/GAP matrix in comparison to AP/HTPB at various pressures up to 15 MPa. The agglomeration of Al particles at the surface and burning behavior of aluminized AP/HTPB propellants has already been investigated and is extended to the ADN/GAP propellants. The temperature measurements close to the propellant surface indicate higher values near the Al boiling point that accelerates the melting of Al particles and influences the agglomeration process. At higher pressure the temperatures are in the magnitude of Al2O3 evaporation and decomposition close to 3000 K.