Combustion and agglomeration characteristics of boron particles in boron-containing fuel-rich propellant

The energy release efficiency of boron (B)-containing fuel-rich solid propellants depends largely on the combustion behavior of the B particles contained therein. Here, the combustion process of B particles was first studied using a laser ignition testing system. Then, the combustion and agglomeration characteristics of B particles in a fuel-rich propellant were further investigated. To this end, a microtube burner was specially manufactured to mimic the secondary combustion of boron-containing propellant. Results show that the primary combustion intensity of the boron-containing propellant was relatively weak, and the combustion temperature was 1720±32 K. B particles would participate in the primary combustion reaction of the propellant, resulting in short time detection of the characteristic green flame and BO2 spectrum. Severe self-conglomeration of B particles occurred on the propellant burning surface, forming irregular coral-like B particle conglomerates. The development of the quasi-secondary (the word “quasi” is added to highlight the difference between the experimental conditions and the actual conditions in engines) combustion flame showed that hot B particles were an important ignition source for the gaseous fuel and that the existence of excess gaseous fuel in the primary plume was an important prerequisite for self-sustaining combustion of B particles in air. The emission spectra of propellant quasi-secondary combustion were very similar to those of primary combustion, but the intensity was significantly increased. Microstructures of the combustion residues showed that the oxide layer on the surface of B particles played an important role during the formation of B conglomerates. Irregular B conglomerates detached from the propellant burning surface might further develop into spherical B agglomerates in the high-temperature secondary combustion flame zone.