The amount of mass injected into the airbag needs to be defined with respect to time.
This is required as a function.
The specific heat, , along with a function defining the change in temperature with
time is required.
The data can be obtained by two methods:
Possibly from the airbag manufacturer
From a tank experiment
A diagram of a tank experiment can be seen in Figure 1.Figure 1. Tank Experiment
The mass versus time curve can be derived from the pressure curve if
is known:
Where, is the molecular weight of the injected gas. is the perfect gas constant: ; .
The average estimate for temperature of injection is:
Where,
Total pressure variation during the experiment
Total injected mass, which can be derived from the mass of propellant in the
pyrotechnic inflator and the chemical reaction; 40% is a typical value for the ratio
of the produced mass of gas to the solid propellant mass.