An investigation of the performance of a boron/potassium-nitrate based pyrotechnic igniter

The performance of a boron/potassium-nitrate based pyrotechnic igniter, used as an initiator in airbag gas generators, was investigated at different initial temperatures. Igniter firings were conducted in a small vented combustion chamber in order to measure the instantaneous chamber pressures. A theoretical model, which considers multi-phase products and lumped chamber parameters, was adopted to determine the discharging gas phase and condensed phase mass flow rates from the igniter. The data reduction model used experimentally obtained pressure-time traces and the total burned mass as input data. The calculated instantaneous mass flow rates of the igniter at various initial temperatures showed that the initial temperature has a major influence on the igniter's performance. For the temperature range tested (-20°C to 60°C), the pressurization rate and the total mass flow rate of the igniter increased with temperature and ranged from 322 GPa/s to 721 GPa/s and 4.3 kg/s to 6.1 kg/s, respectively. It was found that the condensed-phase products comprised the majority of the igniter discharge products. The mass fraction of the condensed-phase products indicated a weak dependency on initial igniter temperature. Under similar test conditions, the recorded pressure-time traces during igniter firings were found to be quite reproducible.