Detonation Characteristics of Some Dusts and Liquid/Dust Suspensions (Ignition Delay, Induction Zone, Three-Phase).

Abstract

A combination of experimental and theoretical study was conducted in order to determine the detonation characteristics of a high explosive dust dispersed in air. Towards this end, a special "shock tube" facility was developed wherein the dust was transported through the driven tube by a gas flow. Detonation of the high pressure gases in the driver served to transmit a strong blast wave into the dust mixture. The resultant wave was monitored by pressure switches, pressure transducers, a photodiode, and streak photography in order to ascertain whether detonation was established. Within the limits of the facility, RDX (cyclonite) dust in the air could not be detonated. However, detonation was realized with the larger (37 micron) particles in oxygen enriched air (12% O(,2), 88% air) and with AP (ammonium perchlorate NH(,4)ClO(,4)) additive (83% RDX + 17% AP) in air. The small RDX particles (2 micron), under the same conditions, could not be detonated. A theoretical model was developed to describe the relationship of particle size to detonability of the dust mixture. In this model an unsteady particle heat transfer equation with an Arrhenius type of source team was coupled with the flow conservation equations. Calculation was focused on the induction period. The thermal effects due to the presence of the particles on the flow behind the leading shock wave, but prior to the ignition point, were calculated for various particle sizes and loading ratios. It was shown that a large quantity of very small particles mixed with the gaseous oxidizer would appreciably decrease the gas temperature behind the incident shock wave and hence deter the ignition of the particles. This effect was shown to be much smaller for the case of larger particles, and hence, would seem to explain the experimental finding that the larger particles were easier to detonate. Also, a number of experiments were conducted on shock wave ignition characteristics of liquid fuel drops with entrained small dust particles. The liquid fuel used was decane and the dust included RDX, AP, and inert aluminum oxide. In general, these dusts served to decrease the ignition time delay for the drops and hence would presumably increase the detonability of such a spray.