EXPERIMENTAL STUDY OF FLAME-SPREADING PROCESSES OVER Mg/PTFE/Mg THIN FOILS

An experimental study of flame-spreading behavior over thin Mg/PTFE/Mg foils (called Enerfoil™ Pyrotechnic Film) with thicknesses of 10/25/10 μm was conducted in an argon environment. This thin film pyrotechnic material has been designed to serve as an ignition enhancer in passenger-side airbag gas generators. The objective of this study was to determine the effects of initial chamber pressure and gap width between two foils on the intrinsic flame-spreading rate of Enerfoil™ films. In the experimental setup, the steady-state flame-spreading rate (VFS) was deduced from the flame-front trajectory measured by an array of fast-response Lead-Selenide (Pb-Se) IR photodetectors. The initial chamber pressure was varied from 0.1 to 10.5 MPa. Results indicated that for single-foil tests VFS decreased as the initial chamber pressure was increased; this observed trend is believed to be caused by a greater heat loss to the ambient gas at higher pressures. An experimental correlation was developed with a pressure exponent of −0.118. For double-foil tests, the gap width between two adjacent foils was varied from 50 to 400 μm. It was found that for double-foil tests there exists an optimal gap width for obtaining a maximum VFS at a given initial chamber pressure. The optimal gap width appears to become smaller as the initial chamber pressure increases. For each gap width tested, there is also an optimal pressure at which the VFS reaches a maximum. The existence of the optimal pressure and gap width is caused by the combination of several factors, including required physical space for complete gas-phase reactions, heat transfer rates to both unburned foils and ambient gases.