Ultra‐Fine Aluminium Characterization and its Agglomeration Features in Solid Propellant Combustion for Various Quenched Distance and Pressure

Abstract

AbstractAddition of micrometer‐sized aluminium powder in solid propellant increases the specific impulse whereas it also contributes to thrust loss due to two‐phase flow. Aluminium particles form large sized agglomerates during propellant burning. In this context, agglomeration feature of ultra‐fine aluminium (UFAL) in solid propellant combustion is investigated using experimental study. The synthesized UFAL powder is used with the intensity weighted harmonic mean size of 438 nm which is produced by RF induction plasma method. The morphology and purity of the UFAL is verified using SEM and EDAX studies respectively. The ultra‐fine particles are also characterized using gas volumetric method, surface area measurement and XRD analysis. Quench particle collection technique is adopted to estimate the aluminium agglomerate measurement over the pressure ranges from 2 MPa to 8 MPa. The flame quenching distance from the propellant burning surface is varied from 5 mm to 71 mm to estimate the effect on agglomerate size. The inherited residual forces of UFAL strongly influences the agglomeration process, and also the aluminium agglomerate sizes vary from propellant burning surface towards the complete aluminium combustion. The XRD and XPS results of the agglomerates show that the aluminium content decreases and alumina content increases far away from the burning surface, invariably represents the initiation of combustion process over the considered quenching distances. UFAL powder exhibits significant agglomeration with the size ranging from 11–21 μm. This will substantially benefit from exhaust signature point of view and also reduction in two‐phase flow losses to thrust in contrast to micron sized‐aluminium particles in propellant which displays large sized aluminium agglomerates.