EQUILIBRIUM-ANALYSIS OF 3 CLASSES OF AUTOMOTIVE AIRBAG INFLATER PROPELLANTS

In most vehicle airbag systems, the gaseous mixture which fills the ai rbag comes from rapid combustion of a condensed-phase propellant. An a rea of current interest in the development of airbag systems is the de composition 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 use d in the airbag industry. The propellants discussed in this paper are a sodium-azide (NaN3) propellant, a non-azide propellant containing az odicarbonamide (ADCA), and a double-base propellant (DB). The thermoph ysical properties investigated in this study include the flame tempera ture and chemical composition of the product gases, the number of gase ous moles produced per mass of condensed-phase propellant consumed, th e condensed-phase (slag) production of each propellant, and the toxici ty of gas-phase combustion products. Airbag inflator performance, whic h is a function of the propellant combustion behavior, is often measur ed by reacting a sample of condensed-phase propellant in a rigid combu stion 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 ta nk tests and are widely used in the automotive industry to test and va lidate inflator performance. In this paper, the questionable validity of using such tank tests to adequately describe the deployment of an a irbag will also be addressed.