Trevor D. Hedman

Experimental Investigation of the Decomposition Preceding Cookoff in a Composite Propellant

The decomposition preceding autoignition of an ammonium-perchlorate-based composite propellant was experimentally investigated. Autoignition temperature is measured for a selected heating rate. At that same heating rate, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and hot-stage microscopy are employed to study the propellant behavior leading to reaction. These experiments are conducted on both cured composite propellant and individual ingredients, including neat ammonium perchlorate and a cured binder. For a heating rate of 2 °C/min., it is determined using thermogravimetric analysis/Fourier transform infrared that ammonium perchlorate and the binder begin to react together near 150°C, whereas differential scanning calorimetry shows initial exothermic behavior after the orthorhombic-to-cubic phase transition near 240°C. This disparity is discussed and further investigated using larger-scale cubes of propellant heated in ovens at the same heating ...

Flame Structure Study of a Bimodal Ammonium Perchlorate Composite Propellant Using 5 kHz PLIF

The self-deflagration of a bimodal ammonium perchlorate (AP) and hydroxyl-terminated polybutadiene (HTPB) propellant was studied using high speed planar laser induced fluorescence (PLIF) for the first time. The qualitative OH concentration was characterized near the surface. In addition to OH, it was found that the larger AP particles can be imaged as they fluoresce when exposed to laser radiation centered at 283.2 nm. Single AP particle ignition delay, lifetime, and flame height are determined as a function of particle diameter over a range from 100 to 500 μm at 1 atm within the burning sample. High speed visible imaging was also completed to confirm the trends seen during PLIF experiments, although the fluoresced particles have much improved contrast. Ignition delay times and single particle burn times were compared with a model proposed by Shannon and Peterson. The measured final diffusion flame height above a regressing AP crystal was compared with an expression used by the Beckstead, Derr, and Price (BDP) model. It was found that the AP/HTPB propellant flame structure varies significantly with particle size, even at 1 atm. The models are found to adequately predict the observed trends, but do not capture the interaction of adjacent particles. It is shown that high speed OH PLIF can be a valuable tool to characterize AP composite propellant combustion.