Imaging and Spectral Measurements of Explosions

A document describes experiments performed to investigate rates of delivery of energy onto targets from different explosive formulations. The experiments were designed to measure relative positions of blast fireballs and leading shock fronts; determine whether different explosive formulations exhibit unique spectral signatures; determine temperatures of gases and solids near fireball surfaces; and measure rates of heating as functions of time. In the experiments, unconfined explosions were observed using time-resolved laser shadowgraphy, spectrometry integrated over the first 50 ms following initiation, time-resolved three-wavelength pyrometry, and time-resolved heat-flux measurements.

Different explosives tested produced fireballs having different peak temperatures at ≈1 ms after initiation. For all explosives, fireball temperature varied relatively slowly from ≈5 to ≈55 ms after initiation. Pyrometer and heat-flux measurements were interpreted as suggesting that fireballs consist of collections of flamelets. Shadowgraphs were interpreted as suggesting that fireballs attain nearly full volume and then burn towards maximum heat flux. For aluminized explosives, spectral features at wavelengths near 394 nm and 396 nm from gas-phase aluminum and a band at 484 nm from gas-phase AlO were used as indications of burning of aluminum and as secondary sources of temperature information.

This work was done by Thuvan Piehler, Barrie Homan, Rachel Ehlers, Richard Lottero, and Kevin McNesby of the Army Research Laboratory. ARL-0040

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