Remedial start method in a fuel cell
A remedial method for starting a fuel cell system is described. The method includes determining if the remedial method is required; providing air to an exhaust of a fuel cell stack; setting a hydrogen flow rate to an anode side of the fuel cell stack; providing a predetermined volume of hydrogen to the anode side of the fuel cell at the hydrogen flow rate; providing a predetermined volume of air to a cathode side of the fuel cell stack after the predetermined volume of hydrogen has been provided to the anode side while continuing to provide air to the exhaust of the fuel cell stack and hydrogen to the anode side of the fuel cell stack; determining if a stack voltage is stable after the predetermined volume of air has been provided to the cathode side; and closing the anode outlet valve after the stack voltage is stable.
1. A remedial method for starting a fuel cell system comprising:
determining if the remedial method is required;
providing air to an exhaust of a fuel cell stack;
setting a hydrogen flow rate to an anode side of the fuel cell stack;
providing a predetermined volume of hydrogen to the anode side of the fuel cell at the hydrogen flow rate;
providing a predetermined volume of air to a cathode side of the fuel cell stack after the predetermined volume of hydrogen has been provided to the anode side while continuing to provide air to the exhaust of the fuel cell stack and hydrogen to the anode side of the fuel cell stack;
determining if a stack voltage is stable after the predetermined volume of air has been provided to the cathode side; and
closing an anode outlet valve after the stack voltage is stable.
2. The method of claim 1 wherein the hydrogen flow rate is set using an anode to cathode exhaust pressure difference.
3. The method of claim 2 wherein the hydrogen flow rate is controlled to a hydrogen emissions exhaust target.
4. The method of claim 1 wherein the hydrogen flow rate is set using the following equations:
n
.
H
2
Vlv
=
Y
H
2
Exh
n
.
Air
Exh
1
-
Y
H
2
Exh
where,
{dot over (n)} H z Vlv is desired hydrogen flow through an anode outlet valve
Y H 2 Exh is the target exhaust hydrogen concentration {dot over (n)} Air Exh is the available air flow for dilution in the exhaust
P
An
=
[
(
n
.
H
2
Vlv
*
4.633
K
v
)
2
*
MW
*
T
+
P
Exh
2
]
where,
P An is the anode pressure set point
{dot over (n)}H 2 Vlv is the desired hydrogen flow as previously calculated
K v is the equivalent valve flow coefficient
MW is the molecular weight of hydrogen
T is the the gas temperature
P Exh is the exhaust (downstream) pressure.
5. The method of claim 1 wherein the hydrogen is provided to the anode side of the fuel cell stack by opening a hydrogen supply valve and an anode outlet valve.
6. The method of claim 1 wherein determining if the remedial method is required comprises determining whether the fuel cell system suffered a quick stop, a failed start, or a lost battery voltage.
7. The method of claim 1 wherein the predetermined volume of hydrogen is in a range of about 1 to about 3 anode volumes.
8. The method of claim 1 wherein the predetermined volume of air is in a range of about 1 to about 3 cathode volumes.
9. The method of claim 1 wherein the predetermined stack voltage is in a range of about 600 mV to about 900 mV per cell.
10. The method of claim 1 wherein a ratio of an amount of air provided to the cathode side of the fuel cell to an amount of air provided the exhaust of the fuel cell is less than about 10%.
11. The method of claim 1 further comprising closing a high voltage contactor after introducing air to the cathode side of the fuel cell stack when a predetermined stack voltage is obtained.
12. The method of claim 1 further comprising closing a high voltage contactor before determining the stack voltage.
13. The remedial method of claim 1 , wherein the anode outlet valve is selected from a drain valve, an exhaust purge valve, and a back pressure valve.
14. The remedial method of claim 4 , wherein {dot over (n)} H z Vlv is the desired hydrogen flow through a drain valve, an exhaust purge valve, or a back pressure valve.
15. A remedial method for starting a fuel cell system comprising:
determining if the remedial method is required;
providing air to an exhaust of a fuel cell stack;
setting a hydrogen flow rate to an anode side of the fuel cell stack using the following equations:
n
.
H
2
Vlv
=
Y
H
2
Exh
n
.
Air
Exh
1
-
Y
H
2
Exh
where,
{dot over (n)} H z Vlv is desired hydrogen flow through an anode outlet valve
Y H 2 Exh is the target exhaust hydrogen concentration
{dot over (n)} Air Exh is the available air flow for dilution in the exhaust
P
An
=
[
(
n
.
H
2
Vlv
*
4.633
K
v
)
2
*
MW
*
T
+
P
Exh
2
]
where,
P An is the anode pressure set point
{dot over (n)} H 2 Vlv is the desired hydrogen flow as previously calculated
K v is the equivalent valve flow coefficient
MW is the molecular weight of hydrogen
T is the gas temperature
P Exh is the exhaust (downstream) pressure;
providing a predetermined volume of hydrogen to the anode side of the fuel cell at the hydrogen flow rate;
providing a predetermined volume of air to a cathode side of the fuel cell stack after the predetermined volume of hydrogen has been provided to the anode side while continuing to provide air to the exhaust of the fuel cell stack and hydrogen to the anode side of the fuel cell stack;
determining if the stack voltage is stable after the predetermined volume of air has been provided to the cathode side; and
closing the anode outlet valve after the stack voltage is stable.
16. The method of claim 15 wherein the hydrogen is provided to the anode side of the fuel cell stack by opening a hydrogen supply valve and an anode outlet valve.
17. The method of claim 15 determining if the remedial method is required comprises determining whether the fuel cell system suffered a quick stop, a failed start, or a lost battery voltage.
18. The method of claim 15 wherein the predetermined volume of hydrogen is in a range of about 1 to about 3 anode volumes.
19. The method of claim 15 wherein the predetermined volume of air is in a range of about 1 to about 3 cathode volumes.
20. The method of claim 15 wherein the predetermined stack voltage is in a range of about 600 mV to about 900 mV per cell.
21. The method of claim 15 wherein a ratio of an amount of air provided to the cathode side of the fuel cell to an amount of air provided the exhaust of the fuel cell is less than about 10%.
22. The method of claim 15 further comprising closing a high voltage contactor after introducing air to the cathode side of the fuel cell stack when a predetermined stack voltage is obtained.
23. The remedial method of claim 15 , wherein the anode outlet valve is selected from a drain valve, an exhaust purge valve, and a back pressure valve.