Fast-response optical diagnostics (a time-integrated spectrometer and two separate fast-response three-color pyrometers) are used to record the transient visible radiation emitted by a fireball produced when a condensed explosive is detonated. Measurement of the radiant intensity, in several narrow wavelength bands, is used to estimate the temperature of the condensed products within the fireball. For kg-scale conventional oxygen-deficient homogeneous TNT and nitromethane explosive charges, the radiant intensity reaches a maximum typically after tens of milliseconds, but the measured fireball temperature remains largely constant for more than 100 ms, at a value of about 2,000 K, consistent with predictions using equilibrium thermodynamics codes. When combustible metal particles (aluminum, magnesium or zirconium) are added to the explosive, reaction of the particles enhances the radiant energy and the fireball temperature is increased. In this case the fireball temperatures are lower than equilibrium predictions, but are consistent with measurements of particle temperature in single particle ignition experiments.

The detonation performance of a more than 70,000 m 3 fuel spray-air cloud is experimentally investigated using dispersal of a 5,090 kg gasoline payload by a central explosive in a cylindrically stratified configuration. The large-scale explosive dispersal data are further analyzed, together with a revisit of the data from previously conducted small-scale experiments and numerical simulations, to study particle jetting instabilities. The experiments depict a dual hierarchical jet structure consisting of primary particle jets overlapped by fine particle jets on the primary surfaces. Both jet systems form within the expansion of 1.5-2 times the initial charge diameter. The fine droplet jets are numerous initially as a result of surface instabilities or fragmentation of the charge casing, while the primary jets have a limited number emerging out of the surface of fine jet structures later in time. The number of primary jets is consistent with the number of incipient radial fractures observed at the payload surface. From this fact, an instability mechanism is suggested that the formation of primary particle jets may originate in the perturbations that develop near the interior interface between explosive and payload, through non-uniform density effects or casing fragmentation, driven by the explosive detonation and subsequent expansion of the high-pressure detonation products. Numerical modeling using liquid payload fragmenting into droplet particles has been applied to investigate the proposed mechanism. The numerical results show that the high-pressure jets of detonation products, created from the interior casing fragmentation, radially fracture the payload. The resulting compressed radial filaments, developed within the payload, lead to the primary jets emerging between the radial fracture points at the payload surface. The number of interior payload filaments before payload surface bursting, and hence the number of primary jets, is controlled by the number of inner casing fragments at the explosivepayload interface. Furthermore, the number of primary jets is also influenced by the mass ratio of payload to explosive and inner casing fragment pattern, whereas the perturbations induced by minor fragments will dissipate through the large payload and not result in final filaments.

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