Controlling the combustion and agglomeration characteristics of a solid composite propellant via a DC electric field

Abstract

This study explores the use of a DC electric field to control the combustion and agglomeration characteristics of a solid composite propellant as typically deployed for rocket propulsion. Experiments were performed in a custom-built reacting flow facility that supports high-speed photography and the collection of condensed combustion products (CCPs). The propellant burning rate, aluminum agglomeration process, CCP size distribution, and combustion efficiency were systematically examined under a range of electric-field voltages (−5 to 5 kV) in both the forward and backward directions. It was found that as the electric-field voltage increased, both the propellant burning rate and combustion efficiency increased, while the degree of aluminum agglomeration decreased, reducing the particle size of the CCPs. The introduction of an electric field can bring about profound effects via particle charge acceleration, Rayleigh crushing, and ion excitation. For example, aluminum near the burning surface can split into smaller particles, the diffusion flames around droplets can exhibit a higher stand-off ratio, and more hollow agglomerates can form, as evidenced by an inspection of scanning electron microscopy images of the CCPs. The electric field was found to have a more pronounced effect in the forward direction than in the backward direction. A physical mechanism was proposed for how an electric field can alter propellant combustion. Through this, the combustion and agglomeration characteristics of solid composite propellants can be precisely tuned with an electric field without resorting to changes in the propellant formulation. The findings of this study contribute to a better understanding of how an electric field can be used to control propellant combustion and thrust in solid rocket motors.