Assessment of Airbag Inflator Characterization Methods for Numerical Prediction in the Automotive Restraint System Applications 2023-01-5029

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.