Primary combustion and near-burning surface conglomeration characteristics of boron-containing fuel-rich propellant

The study of primary combustion and near-burning surface conglomeration characteristics of boron-containing fuel-rich propellant can assist in the comprehension of the primary combustion mechanism. Here, the macroscopic combustion process and particles conglomeration behavior in the vicinity of the burning surface were investigated using a combination of online and offline analysis methods. Concurrently, the size of the relatively large conglomerates escaping from the burning surface was measured online by image measurement methods, and the corresponding size distribution and morphological parameters were provided. The results demonstrate that the combustion of this kind of propellant exhibited an obvious layered structure, characterized by a distinctive phenomenon of a "sedimentary layer". The presence of the sedimentary layer exerted a certain influence on the combustion process. Boron particles could participate in the reaction during the primary combustion process, but appropriate reaction conditions, such as sufficient temperature and oxidizing gas concentration, were required. The accumulation and conglomeration of metal particles were completed under the influence of adhesion and separation forces, with the particles escaping from the burning surface in the form of coral-like conglomerates. The adhesion and detachment of conglomerates on the burning surface led to consistent fluctuations in the shape and height of the combustion flame, as well as the thickness of the sedimentary layer. Furthermore, due to the uneven stress on the conglomerates in the sedimentary layer, it was possible to observe the occurrence of a secondary conglomeration process, whereby small-sized conglomerates were captured by larger conglomerates as they escaped from the burning surface. The coral-like conglomerates consist of B, Mg, and Al monomers and their combustion products. They were widely distributed in the sub- micron to millimeter size range, which was significantly different from the size distribution of the combustion products obtained from the nozzle outlet of the gas generator.