Fuel‐Rich Explosive Energy Release: Oxidizer Concentration Dependence

Abstract

AbstractSmall‐scale detonation experiments were conducted in a controlled atmosphere chamber to investigate the post‐detonation reactivity of a fuel‐rich, plastic bonded explosive. The atmosphere surrounding these 20 g explosive charges was varied in oxygen content from 0.2 to 100% with the total pressure held constant at 101 kPa. The performance of this small‐scale explosive charge is sensitive to the changing atmospheric conditions, perhaps more so than a larger charge size, due to burning inefficiencies corresponding to a scaling effect (increased surface area to volume ratio). Time‐resolved optical emission spectroscopy was used to contrast the dependence of the post‐detonation combustion properties on external oxygen content. The dominant near‐ultraviolet and visible emission features evolve from aluminum (Al) and aluminum monoxide (AlO) when oxygen is present. The time evolution of AlO emission was used to estimate the aluminum particle burning times, which lengthen from 6 to 31 μs as the oxygen content is reduced from 100 to 1%. The absence of AlO spectral features below 1% oxygen levels imply that the emission spectroscopy applied to this detonation environment is most sensitive to the aerobic component of the post‐detonation combustion. Pressure and optical pyrometry measurements recorded during the same experiments exhibit the strong dependence of the early time energy release on the oxygen content in the surrounding atmosphere. Numerical simulations of the detonation and subsequent multiphase flow expansion predict the position of the fuel particles to extend beyond the detonation products and, in some cases, beyond the shock front during the timescales covered in these experiments, stressing the importance of mixing with ambient oxygen for early combustion to occur.