MODELING AND NUMERICAL-SIMULATION OF THE INTERNAL THERMOCHEMISTRY OF AUTOMOTIVE AIRBAG INFLATORS

This paper provides a comprehensive description of the coupled thermoc hemical processes that occur during the firing of an automotive airbag inflator. A mathematical model is developed to simulate the transient , thermochemical events associated with ignition and combustion of a p yrotechnic automotive airbag gas-generator unit (inflator). The govern ing equations for the airbag inflator model are derived by expressing conservation conditions for mass and energy in the interior combustion chamber, filter/cooling screens, exterior plenum, and discharge tank. Following a brief description of the model development and physical a ssumptions made in the analysis, two series of test calculations are p resented. The first series of calculations is for a baseline test case of a conventional pyrotechnic inflator system that is characteristic of a standard discharge tank validation experiment. Transient pressure and temperature profiles generated by the airbag inflator model are p resented along with properties at the exit nozzles. A parametric study demonstrates the usefulness of airbag inflator simulations in assessi ng the sensitivity of airbag pressure curves to various design paramet ers such as propellant and hardware properties and hardware dimensions . The second series of calculations illustrates the influence of pre-p ressurized inert gas on the performance of a pre-pressurized pyrotechn ic inflator system. Performance of the inflators is measured in terms of pressure-time and temperature time profiles in the inflator and dis charge tank as well as pressure time integrals at specified times afte r ignition. The pre-pressurized pyrotechnic inflator shows certain adv antages over conventional pyrotechnic units, including significantly l ower requirements for solid propellant mass, lower operating temperatu re, more uniform performance at hot and cold ambient conditions, and h igher thermal efficiency The chemical composition of the inert gas, pr e-pressurized system is also shown to influence the working process of the inflator.