Experimental Study of Aluminum Combustion in Solid Propellant by Using Photomicrography and Digital In-Line Holography

Aluminum (Al) combustion is an important research area for improving the performance of solid propellants. During the combustion of the solid propellant, aluminum particles can form large-sized agglomerates that may result in poor combustion performance, losses of two-phase flow and even affects the combustion stability of solid rocket motors. Therefore, to obtain the combustion characteristics of aluminum particles in solid propellants is of great importance. Due to the complex combustion environment of solid propellants, diagnostics of dynamic combustion process of aluminum particle are difficult. A few measurement methods can be used. In order to study the combustion characteristics of aluminum particles, photomicrography and digital in-line holography are proposed for the research in this paper. In current work, a combustor was used for the combustion experimental of solid propellants under atmospheric pressure. In addition, an optical system was constructed to diagnose the dynamic combustion process of aluminum particles. Base on this optical system, photomicrography and digital in-line holography were successfully applied to the dynamic combustion diagnosis of aluminum particles. From microscopic images, the dynamic processes of accumulation, aggregation and agglomeration of aluminum particles on the burning surface were captured, some detailed movement processes were analyzed. Considering the limitation of the depth of field in photomicrography method, digital in-line holography was used to obtain the dynamic combustion process of aluminum particles in the plume. The results show that both methods can capture the dynamic combustion process of aluminum particles. The three stages of agglomerate formation on the burning surface were obtained clearly, and the second mergence process of agglomerates was also captured. In general, the methods proposed in this paper can be effectively used in the study of aluminum combustion and provide more useful data for establishment of aluminum combustion model.