Investigation of Reaction Propagation in Commercially Available Shock Tubes

Abstract

The shock tube (also known as the detonation transmission tube or by the trade name ‘NONEL’) is part of a non-electric ignition system widely used in mining and construction applications. A shock tube is a thin, hollow plastic tube with a small amount of explosive, usually HMX/Al-based, deposited on its inner wall. The purpose of the NONEL is to transmit an initiation signal to the ignition element (detonator). However, the exact principle of reaction propagation is not yet fully scientifically understood. In this work, several commercially available shock tubes were compared. The flame propagation and associated processes of transition from deflagration to detonation were recorded using high-speed imaging techniques. The recordings were evaluated in the form of x-t and v-x diagrams. From there, the speed of reaction propagation was determined in various sections of the tube. The tubes were also instrumented with piezoelectric pin sensors for shock wave arrival time detection. The position of the shock wave relative to the radiant reaction area in the tube could then be observed. The results demonstrate that in the initial stages, at velocities lower than 1500 m·s-1, the shock wave precedes the radiant region and the reaction proceeds in a deflagration regime. At higher velocities (greater than 1500 m·s-1), the signal arrival at the piezoelectric pin sensor coincides with the radiant region and the reaction regime transits to detonation.