In most vehicle airbag systems, the gaseous mixture which fills the airbag comes from rapid combustion of a condensed-phase propellant. An area of current interest in the development of airbag systems is the decomposition behavior of these condensed-phase propellants over a range of operating conditions. The purpose of this paper is to examine the performance of gas-generating propellants by comparing the theoretical combustion behavior of three condensed-phase propellants commonly used in the airbag industry. The propellants discussed in this paper are a sodium-azide (NaN3) propellant, a non-azide propellant containing azodicarbonamide (ADCA), and a double-base propellant (DB). The thermophysical properties investigated in this study include the flame temperature and chemical composition of the product gases, the number of gaseous moles produced per mass of condensed-phase propellant consumed, the condensed-phase (slag) production of each propellant, and the toxicity of gas-phase combustion products. Airbag inflator performance, which is a function of the propellant combustion behavior, is often measured by reacting a sample of condensed-phase propellant in a rigid combustion chamber initially filled with nitrogen or air and observing the pressure-time relationship, the temperature-time relationship, and the final product composition. Such investigations are commonly called tank tests and are widely used in the automotive industry to test and validate inflator performance. In this paper, the questionable validity of using such tank tests to adequately describe the deployment of an airbag will also be addressed.
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