Combustion characteristics of advanced nitramine-based propellants

Abstract

The combustion of HMX (cyclotétramethylene tetranitramine) based propellants was studied in a window bomb with high speed motion picture photography. The HMX concentration was varied from 20 to 60% by weight with the remaining material being an active binder composed of nitrocellulose and nitroglycerin. A new technique using a powerful He−Ne Laser was developed to measure burning rate characteristics over the pressure range from 10 to 350 atm (150 to 5000 psi). The temperature sensitivity coefficient σ p is determined in the interval from −40°C to +80°C. The present experiments included high speed cinephoto-micrography of the combustion zone and scanning electron microscope study of the extinguished surface which helped to clarify the combustion mechanism. The data show the influence of HMX mass loading and particle size on the burning rate characteristics. Because of the diffusion flame, the addition of small concentrations of ammonium perchlorate (AP) is effective in increasing the burning rate and decreasing the pressure exponent. On the other hand, AP markedly increases the temperature sensitivity coefficient. The cinemicrography study of the combustion of nitramine propellants shows that previous speculations regarding the ejection of HMX particles from the burning surface are erroneous. The glowing agglomerates which appear on the surface are emitted by the double base matrix. The HMX particle size has no influence on the agglomerate dimensions which are considerably more important in the case of nitramine propellants prepared by the casting process. A 5 minute movie consisting of selected film clips from the experiments will be shown. It provides great detail on the processes occuring at the burning surface of nitramine propellants.