Experimental and Model Study of Agglomeration of Burning Aluminized Propellants

Agglomerate sizes of ammonium perchlorate/cyclotrimethylene trinitramine/aluminum/hydroxyl-terminated polybutadiene propellants with virgin aluminum sizes of 7, 17, and 30 μm were measured by a cinephotomicrography experimental technique under 300- (2.07-) and 1000-psi(6.89-MPa) pressures. The measured sizes followed a log-normal distribution. A decrease in the virgin aluminum size leads to an increase in the mean agglomerate size. The effect diminishes when the aluminum size increases or the pressure decreases. Gany and Caveny's theory indicates that the virgin aluminum size/mobile molten layer thickness controls the degree of agglomeration. Their theory was tested and validated using data obtained from three different propellant systems. Agglomerate size data from 14 different sources in the literature were carefully reviewed. These data were obtained from aluminized composite propellants containing two different types of oxidizer: ammonium perchlorate and ammonium perchlorate and cyclic nitramines. A new agglomeration parameter A that is a function of burning rate and propellant formulation is proposed to correlate the selected 126 agglomerate size data including 6 experimental data generated in the study. It was found that the proposed new agglomerate size model can better explain the literature data for both ammonium perchlorate/aluminum/rubber and ammonium perchlorate/nitramine/aluminuni/rubber propellants rather than the Hermsen model over a wide range of experimental conditions. Validity of the new model was tested with data from a recent publication.