Characterization of output mass and energy fluxes of a pyrotechnic igniter

Pyrotechnic initiators (igniters) have been utilized in a broad variety of combustion systems including airbag inflation systems, aircraft seat-ejection devices, fireworks, artillery systems and many others. A potassium-nitrate based pyrotechnic igniter was used in this investigation. The Special Devices Incorporated (SDI) igniter is used as the initiator in the Talley airbag inflation system. The SDI initiators used for this study contained a 35 mg ignition charge of zirconium/potassium perchlorate and 200 mg of boron/potassium nitrate. A theoretical model which considers multi-phase products was adopted to determine the discharging gas-phase and condensed-phase mass flow rates from the igniter, using empirically obtained pressure-time traces and the total burned mass as input data. The instantaneous mass flow rates of the SDI igniter were obtained for various initial temperatures. It was found that the initial temperature has a major influence on the igniter's performance. For the temperature range tested (-20 to 60 °C), the total mass flow rate of the igniter increased with temperature and ranged from 4.3 to 6.1 kg/s. The pressurization rate and mass flow rate decreased with decreasing initial igniter temperature. It was found that the condensed-phase products comprised the majority of the igniter discharge materials. The mass fraction of the condensed-phase products, ψ_s, was found to be 77% at 60 °C, 78% at 15 °C, and 80% at-20 °C, indicating a weak dependency on initial igniter temperature. The average igniter mass burned for this investigation was 0.228 grams.