Characterization of output mass and energy fluxes of a pyrotechnic igniter

Abstract

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 SD1 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 determ ine 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 SD1 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, Y,, 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. Nomenclature Greek Svmbols Svmbols Fs average density of condensed-phase, kg/m3 A, c, area at the nozzle throat, m* P density, kg/m3 specific heat at constant-pressure, J/kg-K Y specific heat ratio C” specific heat at constant volume, J/kg-K r gamma function for isentropic nozzle flow E total energy, J Y mass fraction h enthalpy, J/kg Ia kinetic energy, J/kg Subscrints M mass, kg p” mass flow rate, kg/s g gas-phase pressure, Pa or MPa in coming into the control volume PE potential energy, J/kg out going out of the control volume R gas constant, J/kg-K solid phase particle T temperature, K & control volume hloss time, s f flame ,heat losses, J ‘, c chamber velocity, m /s 0 initial condition “v volume, m3 ign igniter B Ph. D. Student, PSU, Student Member AX4 + Ph. D. Candidate, PSU, Student Member AIAA $ Distinguished Professor of Mechanical Engineering, PSU, Fellow AX4 * Research Assistant, PSU # Manager of Advanced Air-bag Development Group, Talley Defense Systems n Principal Engineer, Talley Defense Systems,’ Associate Fellow AIAA ‘1 American Institute of Aeronautics and Astronautics