THEORETICAL SIMULATION OF COMBUSTION AND INFLATION PROCESSES OF TWO-STAGE AIRBAG INFLATORS

ABSTRACT

Two-stage airbag inflators are capable of providing an adjustable output for the protection of out-of-position occupants. The objective of this research is to establish a theoretical model and computer code for simulating and understanding the combustion and inflation processes of two-stage airbag inflators burning in fixed-volume discharge tanks. The model is based on the transient conservation equations of mass, species, and energy for the two combustion chambers of the inflator and the discharge tank. This theoretical model is solved numerically, and the calculated results are in good agreement with the experimental data. Simulation results indicate that the pressure–time histories in the two combustion chambers and the discharge tank exhibit different characteristics. The pressure–time history in the first-stage combustion chamber shows two pressure peaks, whereas there is only one pressure peak in the second-stage combustion chamber. The pressure in the discharge tank varies slowly due to its large volume. The effects of ignition delay of the second-stage igniter, mass distribution of gas-generation propellants, and volume ratio of the two combustion chambers on the combustion and inflation processes are studied and reported in this work. This study also performs a sensitivity analysis to investigate the effects of design parameters on the combustion and inflation processes of two-stage airbag inflators. The top three parameters, listed according to their order of influence, are (1) enthalpy of gas-generation propellants, (2) radius of gas-generation propellants, and (3) number of gas-generation propellants.

Keywords:

• two-stage airbag inflator
• out-of-position occupant
• smart restraint system
• numerical simulation

Acknowledgments

This work represents part of the results obtained under the research contract Study of Combustion and Inflation Processes of Two-Stage Inflators sponsored by the Chung Shang Institute of Science and Technology, Taiwan, Republic of China.

Notes

*Calculated by the NASA Chemical Equilibrium Code 76/86.

*Represents the final pressure in the discharge tank.

†Represents that the pressure is lower than that of the baseline condition.