The effects of bimodal aluminum with ultrafine aluminum on the burning rates of solid propellants

Burning rates were measured for aluminized composite propellants with different aluminum (Al) sizes (monomodal distribution), and with bimodal Al distributions containing various amounts of ultrafine Al (UFAl). Enhanced rates were found for fine Al, with the enhancement increases for reduced Al size. The fine Al also burned in an intense region very close to the propellant surface, suggesting improved heat feedback in the form of radiation and conduction. Major modification of the burning rate could be achieved with moderate amounts of UFAl. Results obtained with various fine oxidizer particle sizes and mass fractions suggest that the degree of burning-rate modification depends on the ability to ignite the UFAl, for example, with leading-edge flames, as well as the availability of oxidizer near the Al-containing regions of the propellant.