Fuel cell exhaust dilution control

A fuel cell, comprising:

• an anode, a cathode, an electrolyte positioned between the anode and the cathode;
• and
• a controller adapted to:
• initiate selective purging of reacted fuel gas within the anode of the fuel cell;
• initiate air flow through the fuel cell necessary to dilute a concentration of hydrogen present within the reacted fuel gas exhausted from the fuel cell prior to opening an anode valve adapted to allow reacted fuel gas within the anode to vent from the fuel cell;
• and
• open the anode valve after the air flow through the fuel cell reaches an estimated required air flow rate necessary to dilute the level of hydrogen present within the reacted fuel gas exhausted from the fuel cell.

A vehicle having a fuel cell propulsion system including at least one fuel cell, comprising:

• an anode, a cathode, an electrolyte positioned between the anode and the cathode;
• and
• a controller adapted to:
• monitor, with a first sensor or model in communication with the controller, a concentration of hydrogen gas present at the anode of the fuel cell;
• monitor, with a second sensor or model in communication with the controller, the amount of liquid water accumulated in the anode of the fuel cell;
• initiate a selective purge of reacted fuel gas from the anode of the fuel cell when the concentration of hydrogen gas present at the anode is less than a predetermined concentration;
• and
• initiate a selective drain of liquid water from the anode when the amount of liquid water within the anode is more than a predetermined level;
• monitor, with a third sensor or model, a flow rate of air into the fuel cell;
• estimate a required flow rate of air into the fuel cell necessary to dilute the concentration of hydrogen present within the reacted fuel gas below a predetermined level;
• increase, with an air flow device, the flow rate of air into the fuel cell from a normal operating flow rate to the estimated required flow rate to dilute a concentration of hydrogen present within the reacted fuel gas exhausted from the fuel cell to below a target level prior to opening an anode valve adapted to allow reacted fuel gas within the anode to vent from the fuel cell;
• maintain the anode valve in a closed position when the air flow device is unable to increase the flow rate of air into the fuel cell to the estimated required flow rate;
• open the anode valve to allow reacted fuel gas within the anode to vent from the fuel cell after the flow rate of air into the fuel cell is at the estimated required flow rate;
• continuously, while the anode valve is open:
• monitor, with the third sensor or model, the flow rate of air into the fuel cell;
• re-estimate the required flow rate of air into the fuel cell necessary to dilute the concentration of hydrogen present within the reacted fuel gas below the predetermined level based on feedback from the first and second sensors or model and established shutdown leak rates;
• and
• adjust, with the air flow device, the flow rate of air into the fuel cell to the re-estimated required flow rate;
• maintain the flow of air into the fuel cell at the re-estimated required air flow rate;
• hold the anode valve open for a predetermined time period;
• and
• upon closing of the anode valve, reduce, with the air flow device, the flow rate of air into the fuel cell to the normal operating flow rate.