Studies into Laser Ignition of Confined Pyrotechnics

Abstract

AbstractIgnition tests were carried out on three different pyrotechnics using laser energy from the multimode output from an Ar‐Ion laser (av) at 500 nm and a near‐IR diode laser pigtailed to a fibre optic cable and operating at 808 nm. The pyrotechnics investigated were: G20 black powder, SR44 and SR371C. The confined ignition tests were conducted in a specially designed ignition chamber. Pyrotechnics were ignited by a free space beam entering the chamber through an industrial sapphire window in the case of the Ar‐ion laser. For the NIR diode laser, fibre was ducted through a block into direct contact with the pyrotechnic. The Ar‐Ion laser was chosen as this was found to ignite all three pyrotechnics in the unconfined condition. It also allowed for a direct comparison of confined/unconfined results to be made. The threshold laser flux densities to initiate reproducible ignitions at this wavelength were found to be between ∼12.7 and ∼0.16 kW cm−2. Plotted on the ignition maps are the laser flux densities versus the start of ignition times for the three confined pyrotechnics. It was found from these maps that the times for confined ignition were substantially lower than those obtained for unconfined ignition under similar experimental conditions. For the NIR diode laser flux densities varied between ∼6.8 and ∼0.2 kW cm−2. The minimum ignition times for the NIR diode laser for SR371C (∼11.2 ms) and G20 (∼17.1 ms) were faster than those achieved by the use of the Ar‐ion laser. However, the minimum ignition time was shorter (∼11.7 ms) with the Ar‐ion laser for SR44.