Investigation of the detonation of aluminum powder-oxygen mixtures.

Abstract

It is shown that mixtures containing 48 to 64% (by mass) fine aluminum powder in oxygen are detonable. In 26.4-mm-diam tubes the detonation induction distances of these mix- tures are less than 1.6 m; they decrease with increasing aluminum concentration. The det- onation wave speeds for the lean mixtures are approximately 1550 m/sec and decrease slightly with increasing amounts of aluminum in the mixture. The pressures behind the detonation waves were found to be approximately 31 atm for the mixtures examined. The measured detonation speeds and pressures are approximately 9 and 14%, respectively, below the theo- retical values. This deviation is probably caused by incomplete combustion of the alumi- num particles. The detonation waves of these mixtures show the typical characteristics of spin. LTHOUGH the existence of detonation waves in solid fuel-gaseous oxidizer mixtures has been questioned by some researchers, there appears to be evidence that detonation waves can exist in heterogeneous mixtures. When high- energy shock waves were passed through mixtures .of kerosene droplets and gaseous oxidizer (Kling and Maman1), tion waves were obtained with a stoichiometric mixture only after reflection of the incident shock. The measured speeds agreed with the calculated ones. Cramer2 observed detona- tion-like waves propagating through DECH (diethylcyclo- hexane, CioH20) fuel spray-oxygen mixtures. Eraser3 was able to detonate both octane-oxygen and benzene-oxygen mixtures (also initiated with high-energy shock waves). Nicholls et al. 4 also reported detonation-like waves in heterogeneous DECH-oxygen mixtures. Although these observations support the theory that liquid-gas mixtures detonate, they do not permit us to predict the behavior of solid-fuel systems. The combustion of metal powders with gaseous oxidizers was studied by Hartmann and Greenwald.5 They reported that aluminum dust can be ignited easily in air, oxygen, carbon dioxide, and under certain conditions it can react even with nitrogen. Cassel et al. 6 measured the burning velocities of powdered aluminum in various oxygen-nitrogen atmo- spheres. For a 70% oxygen, 30% nitrogen atmosphere, they reported tube burning speeds of approximately 40 cm/sec. Bunsen-burner flame speeds of aluminum powder-oxygen mixtures have been measured previously (not reported) at this laboratory and were found to be approximately 25 cm/sec. Mixtures having low burning speeds are somewhat difficult to detonate.