Mass Injection

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, c p , along with a function defining the change in temperature with time is required.

The data can be obtained by two methods:
  1. Possibly from the airbag manufacturer
  2. From a tank experiment
A diagram of a tank experiment can be seen in 図 1.

図 1. Tank Experiment
The mass versus time curve can be derived from the pressure curve if T in MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamivamaaBa aaleaacaWGPbGaamOBaaqabaaaaa@38DC@ is known:(1)
m ˙ = P ˙ V M γ R T i n

Where, M is the molecular weight of the injected gas. R is the perfect gas constant: R M = c p c v ; γ = c p c v .

The average estimate for temperature of injection is:(2)
T i n = Δ P Δ m V M γ R
Total pressure variation during the experiment
Δ m
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.