Models of aluminum agglomeration in solid propellants

The research progress on the aluminum agglomeration in solid propellants was reviewed. The limitations of present studies was discussed, followed by the analysis of valuable research directions of agglomeration models in future. The physical process of aluminum agglomeration can be divided into three stages, accumulation, aggregation and agglomeration. The present agglomeration models may be classified to five categories, which are empirical model, pocket model, physical model, random packing model and condensed-layer model, respectively. Highly accurate and widely applicable models used to predict the aluminum agglomeration behavior is still lacking. Developing new agglomeration models which can predict the size distribution of the agglomerates with low computational expense will be a hot issue in future. Physical model is promising due to its capability of the description of agglomeration nature. The combustion experiments of aluminized propellants was conducted at pressure of 5 MPa, and agglomerate diameters on the propellants burning surface were obtained by a high-speed camera coupled with a microscope. The experimental results were compared with the prediction results of Hermsen model and Salita model. The prediction errors of agglomeration diameter are 8.7% and 9.6% by Salita model, for propellants with burning rate of 5.1 mm/s and 8.0 mm/s, respectively, whereas the prediction error reachs 19.2% by Hermsen model for the high burning rate propellant. Overall, it is shown that Salita model has a more reasonable accuracy.