Characterization of an Aluminum–Lithium-Alloy-Based Composite Propellant at Elevated Pressures

Abstract

Aluminum (Al)/lithium (Li)-alloy-based fuels can potentially improve composite propellant performance and reduce hydrochloric acid formation. Shattering microexplosions have been observed in Al–Li-based composite propellants at 0.1 MPa; however, combustion characterization of Al–Li-based propellant as a function of pressure has not been performed previously. Measurement of the burning rate of an Al–Li composite propellant and quantification of agglomerate production near the propellant surface at various pressures are presented in this work. Al–Li particle agglomeration, determined to be unconsumed Al–Li, increased with increasing pressure, suggesting that microexplosions were inhibited at higher pressures. Burning rate experiments demonstrated a plateau burning rate effect that occurred in propellant with fine grade (mean diameter: ) Al–Li particles, whereas the as-received Al–Li-containing (mean diameter: ) propellant maintained a constant pressure exponent of about 0.39 over all pressures tested. The finer Al–Li propellant had a pressure exponent of 0.59 at pressures below about 4 MPa and a pressure exponent of 0.11 above 4 MPa. Surface imaging of the Al–Li propellant showed a distinctive condensed phase reaction on the surface, which became more prominent with the finer Al–Li particles and at higher pressures: a potential source of the plateau burning rate effect.