Document ID: chunk:federal_register_of_legislation:F2015L02109:body:0:p31
Version: federal_register_of_legislation:F2015L02109
Segment Type: other
Provision Reference: 
Character Range: 90416–93067

Δt, starts when the vehicle comes to rest after the impact and continues for at least 60 minutes.

4.1.2.                        The time interval, Δt, shall be increased if necessary in order to accommodate measurement accuracy for a storage system with a large volume operating up to 70MPa; in that case, Δt can be calculated from the following equation:

Δt = VCHSS x NWP /1000 x ((-0.027 x NWP +4) x Rs – 0.21) -1.7 x Rs

where Rs = Ps / NWP, Ps is the pressure range of the pressure sensor (MPa), NWP is the Nominal Working Pressure (MPa), VCHSS is the volume of the compressed hydrogen storage system (L), and Δt is the time interval (min).

4.1.3.                        If the calculated value of Δt is less than 60 minutes, Δt is set to 60 minutes.

4.2.                              The initial mass of hydrogen in the storage system can be calculated as follows:
Po' = Po x 288 / (273 + T0)

ρo' = –0.0027 x (P0')2 + 0.75 x P0' + 0.5789

Mo = ρo' x VCHSS

4.3.                              Correspondingly, the final mass of hydrogen in the storage system, Mf, at the end of the time interval, Δt, can be calculated as follows:
Pf' = Pf x 288 / (273 + Tf)
ρf' = –0.0027 x (Pf')2 + 0.75 x Pf' + 0.5789
Mf = ρf' x VCHSS
where Pf is the measured final pressure (MPa) at the end of the time interval, and Tf is the measured final temperature (°C).
4.4.                              The average hydrogen flow rate over the time interval is therefore:
VH2 = (Mf-Mo) / Δt x 22.41 / 2.016 x (Ptarget /Po)
where VH2 is the average volumetric flow rate (NL/min) over the time interval and the term (Ptarget/Po) is used to compensate for differences between the measured initial pressure (Po) and the targeted fill pressure (Ptarget).

5.                                   Post-crash leak test measurement for a compressed hydrogen storage system filled with compressed helium
5.1.                              The helium gas pressure, P0 (MPa), and temperature T0 (°C), are measured immediately before the impact and then at a predetermined time interval after the impact.
5.1.1.                        The time interval, Δt, starts when the vehicle comes to rest after the impact and continues for at least 60 minutes.
5.1.2.                        The time interval, Δt, shall be increased if necessary in order to accommodate measurement accuracy for a storage system with a large volume operating up to 70 MPa; in that case, Δt can be calculated from the following equation:
Δt = VCHSS x NWP /1000 x ((-0.028 x NWP +5.5) x Rs – 0.3) – 2.6 x Rs
where Rs = Ps / NWP, Ps is the pressure range of the pressure sensor (MPa), NWP is the Nominal Working