A competent numerical prediction on automotive restraint systems relies on
accurate inflator characteristics as input data, which are specified to gas
species composition, mass, and energy flow rate. Due to the highly transient
processes under extreme temperature conditions of inflator deployment, the
determination of inflator characteristics is very challenging. Current
conventional methods utilizing tank pressure (Pt method) and/or chamber pressure
(Pc-thrust method) measurements obtain numerous assumptions, for which their
compatibility with the applied inflator type is often not considered.
In this work, conventional Pt and Pc-thrust methods are detailed, assessed, and
discussed. One stored gas and two pyrotechnic inflators are taken as scenarios,
for which the interior ballistic models are created based on their design
components and functions. The created inflator features are compared between the
three methods. Further, validations are carried out in computational fluid
dynamics (CFD) simulation on the tank test and finite element method (FEM)
simulation on the Force INdicating Assessment Tool (FINAL) ton test.
Results of the tank test and FINAL ton validation show different evaluations of
the input data, which refers to a fundamental bias in interpreting and utilizing
the inflator characteristics. The mismatch behavior between the two test
environments reveals the inadequacy of using the information of the tank test as
a single data source for airbag-relevant simulations. By assessing the applied
assumptions in the conventional methodologies, it has turned out that the
conventional methods are only appropriate for pyrotechnic-type inflators. Thus,
the numerical ballistic approach is advised for stored gas–type inflators
instead of conventional methods. Also, cross-validation is recommended for
pyrotechnic inflators to adjust the gas amount and temperature level before the
complex simulation takes place. These insights contribute not only to a better
understanding of the inflator gas thermodynamics but also provide a general
guideline for simulation engineers in acquiring more reliable solution in the
restraint system development framework.