Methodology for Designing Gas Generator Systems for the Instantaneous Personal Protection System, 18-9136

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Principal Investigators
P. A. Cox
Walter M. Gray
Erick J. Sagebiel

Inclusive Dates: 03/01/99 - 03/30/01

Background - The major goal of this program is to develop at SwRI the technology to design inflation systems. Special emphasis was placed on application to the instantaneous personal protection system (IPPS), but the technology will have application to inflation systems in general.

Approach - Development of design methodologies requires engineering models to describe bag inflation and the solid-propellant gas-generating processes. Available analytical and numerical models were used and carefully designed experiments were performed to generate an easy-to-use engineering model. Independent models were developed for bag inflation and gas generation, programmed on a personal computer, and combined to provide a numerical model of the complete system.

Accomplishments - Engineering models were developed to describe bag inflation and the solid-propellant gas-generating processes. The models incorporate pressure-dependent burning of the propellant and the use of compressed gas, propellant, or both to drive the system. A test fixture was designed to explore the performance of an erection system and provide data to verify the analytical and numerical model. The fixture simulated the IPPS inflation system, but used a piston in a tube instead of a bag inflation system to avoid potential damage to the fixture from high propellant gas temperatures. Materials were selected that would withstand propellant temperatures without damage.

Experiments were complicated by the need to use available gun propellants, which are formulated to burn at higher pressures than normal airbag inflation propellants. More desirable propellants normally used in inflation systems could not be readily obtained. The use of gun propellants required the addition of rupture disks to the test fixture to increase confinement pressure on the propellant. Although experimental results prior to adding the rupture discs were poor, the performance approved after adding the discs. Some instrumentation problems remained, but sufficiently good results were obtained to permit evaluation of the analytical and numerical model. Some improvements are still needed, but the model reasonably predicts system performance, which satisfies the central goal of this project.

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