Combustion and flame structure of HNF sandwiches and propellants

The combustion of hydrazinium nitroformate (HNF) sandwiches and HNF propellants has been studied in window bombs. Sandwich experiments were carried out up to 1 MPa. The binder in HNFIGAP sandwiches regresses along with the HNF. At the interface of GAP and HNF the regression rate is higher than that of neat HNF. Results of kinetic modeling of the HNF/GAP sandwich structure confii that the final flame temperature is reached closer to the burning surface above the binder slab. The binder in HNIVHTPB sandwiches does not keep up with the oxidizer. The extension above the burning surface is dependent on the pressure. At increasing pressures, the protrusion decreases. HNF/GAP propellants with both coarse and fine (474ym and 1OOpm based on sphere volume) were made with a solid loading of 55%. Both propellants have a burn rate exponent n=O.68+0.02. The difference in burn rate is very small: the propellant with fine HNF burns 4% faster at 5 MPa. The burn rate exponent of a HNF/HTPB propellant containing 73% HTPB is n=1.01+0.05. The HTPB propellant has a lower regression rate thanathe GAP propellant. The sandwich and propellant results show that GAP actively participates in the combustion, whereas HTPB does not contribute to the combustion. NO*, OH* and CN* emission images show that only the GAP sandwich has a clear diffusion flame, close enough to the surface to affect burning rate. Emission images of propellants containing coarse HNF show that only part of the surface is burning simultaneously. The propellant containing fine HNF has a more homogeneous emission from the surface.