Quantification of Internal Fireball Structure of Common Explosives Using Imaging and Spectroscopic Diagnostics

Visualization of hemispherical high explosive detonations over transparent surfaces enables quantification of the spatial distribution of thermochemical structure of the evolving fireball. In this work, we examine fireballs at the 25 gram scale of common explosives including PETN, TNT, Composition B, and HMX and RDX-based polymer bonded explosives, with and without added aluminum. Framing camera imaging is used to quantify the spatial size and morphology of the luminous front region out to several charge diameters, with resolution at the sub-mm scale. The thermal structure of the fireball is characterized by pyrometry and imaging spectroscopy. Fiber probes are embedded in the surface at three locations, and they record the emission at three wavelengths as the luminous front passes each location. From these traces, continuum emission can be fit to a time-resolved ‘temperature’ with some approximations regarding emissivity dependence with wavelength. Imaging spectra taken as a fixed instant in time provide information on the spatial distribution of temperature with either continuum fits or atomic fits to iron atomic spectra. These observations can be used to compare advanced, explicit fireball structure models.