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H₂LIVERefueling simulator
What happens between nozzle click and full tank? Watch example fills of the SAE J2601 MC formula, the dispenser control law: pressure ramp, tank heating, state of charge, and what happens when precooling can't keep up.
- ● CONNECT
- ·2 PULSE / LEAK CHECK
- ·3 MAIN FILL⏸ BANK SWITCH
- ·4 TOP-OFF
- ·5 COMPLETE
FUELING TIME
0 s
DISPENSED
0.00 kg
TANK GAS
20 °C
CONNECT · 0.0 g/s
EXAMPLE FILL OF THE SAE J2601 (MAY2020) LIGHT-DUTY MC FORMULA · SELF-DERIVED COEFFICIENTS · VALIDATED AGAINST A REAL REFUELING (ANONYMIZED)
PRESSURE CLASS
PRECOOLING
AMBIENT
CAT. B · 4.00–7.00 KG H₂ AT 100 % SOC (TABLE 8)
Advanced — communication, station
COMMUNICATION
WITHOUT IR DATA THE END TARGET IS LOWER (EQ. J83)
BANK-SWITCH PAUSES
LOG-TRUE: THE REAL FILL SHOWS THREE (§9.3.2.1)
PRECOOLER
SLOW = OUT OF SPEC AT T30/T20 (EQ. J93 GATE)
Table 7 window of the T40 category. The self-derived coefficients assume App. A's hot case — a compliant station delivers at this temperature within 30 s of mass flow.
Illustrative example fills of the SAE J2601 (MAY2020) light-duty MC Formula and the SAE J2601-5 heavy-duty MCF-HF-G, both with self-derived fill-time data (the standards' own derivation methods applied to our tank model), validated against real refuelings (anonymized) — but not a dispenser control system and no substitute for the standards. SAE J2601 and SAE J2601-5 are trademarks of SAE International; this site is not affiliated with or endorsed by SAE International.
How it works — physics, data sources, scope
The dispenser side runs the selected protocol: the SAE J2601 (MAY2020) light-duty MC Formula, or the SAE J2601-5 heavy-duty MCF-HF-G for truck-size tank systems (250–5000 L, flow classes FM60–FM300). Every second it updates the mass-average fuel temperature (MATC), looks up the allowed fill time, and derives the pressure ramp rate, the corridor the station must stay inside, and the moving end-of-fill pressure target. The vehicle side is a lumped-parameter tank model on NIST real-gas data — for heavy duty an array of tanks, where the largest single tank (TVL) sets the thermal worst case.
The standard's fill-time coefficient tables are licensed content and do not ship. The coefficients here are self-derived with the standard's own Appendix H method: constant-ramp worst-case fills of the boundary vessels, pushed to the 85 °C / 97 % SOC limit. The detail view shows the live corridor, MATC and ramp-rate values the control law is computing.
The model is validated against a real 700 bar refueling (anonymized): fill time, dispensed mass, temperature peak, bank-switch pauses and end-of-fill target all reproduce the logged fill within a few percent.
The failure modes are the point: a warm day with mild precooling is not an abort; the protocol trades speed for safety and the fill slows to a crawl. A precooler that misses its temperature gate is an abort, exactly where the standard prescribes. Both are one click away above.
FREQUENTLY ASKED QUESTIONS
How long does refueling a hydrogen car take?
Under normal conditions (700 bar system, −40 °C precooling, 20 °C ambient) this example fill completes in 3 min 34 s, consistent with the few minutes real SAE J2601 dispensers need. Warm weather with weak precooling does not abort the fill; the protocol trades speed for safety and the fill slows down instead.
Why does a hydrogen tank heat up during refueling?
The incoming gas carries compression work as enthalpy, so a fast fill heats the tank toward the 85 °C material limit. That limit, together with the 97 % state-of-charge cap, is exactly what the SAE J2601 MC formula manages; it is why dispensers precool the gas to −40 °C and control the pressure ramp rate.
What is the SAE J2601 MC formula?
It is the control law real 700 bar dispensers run: every second it updates the mass-average fuel temperature, looks up the allowed fill time, and derives from it the pressure ramp rate, the corridor the station must stay inside, and the end-of-fill pressure target. This simulator implements the MAY2020 light-duty version and the newer SAE J2601-5 heavy-duty MCF-HF-G (60–300 g/s, truck-size tank systems), both with self-derived fill-time data, since the standards’ own tables are licensed content.