Critical conditions for ignition of aluminum particles in cylindrical explosive charges

The critical conditions for the ignition of spherical aluminium particles dispersed during the detonation of long cylindrical explosive charges have been investigated experimentally. The charges consist of packed beds of aluminium particles, ranging in size from 3-114 mu m in diameter, and saturated with sensitized liquid nitromethane (NM). The ignition conditions depend on both the charge and particle diameters with the most reactive particles corresponding to an intermediate size (similar to 54 mu m dia). With increasing charge diameter, three particle reaction regimes are observed: i) sub-critical (no particle reaction), ii) near-critical (reaction at isolated spots, or radial bands or rings), and iii) supercritical (continuous reaction of the particle cloud). To monitor the onset of aluminum oxidation, visible radiation from the charge is recorded, through a slit, with a line spectrometer.