High-Speed Visualization and Piezosensor Monitoring of Shocktube Reaction Propagation

Abstract. Shocktube (also known as detonation transmission tubing, or by the trade name 'NONEL') is part of a non-electrical ignition system that is widely used in mining, construction, military and scientific applications. It is a thin, hollow polymer tube, with a small amount of explosive, usually HMX/Al based, on its inner side. Its purpose is to transmit an initiation signal, whether in the form of detonation or deflagration, to the fuse (detonator). However, the exact principle of reaction propagation is not yet fully satisfactorily explained in the available literature. In this work, nine types of commercially available shocktubes were compared. The flame acceleration and the process of transition from deflagration to detonation were recorded at 1M FPS using a high-speed camera. The recordings were evaluated as x-t diagrams, from which it was possible to determine the rate of reaction propagation in different parts of the tube. The tubes were also fitted with piezosensors to detect the arrival of the shock wave, and by synchronising the recording of the high-speed camera and the piezosensors, the position of the shock wave relative to the radiant reaction region in the tube could be observed. The results demonstrate that in the initial stages, at velocities lower than 1500 m/s, the shock wave precedes the radiant region and the reaction proceeds by deflagration. At higher velocities (greater than 1500 m/s), the arrival of the signal at the piezosensor coincides with the radiant region and the reaction proceeds by detonation.