Abstract: A method is provided for controlling the concentration of nitrogen in a fuel cell stack. The method includes providing a fuel cell stack with cathode passages and anode passages including a valve in communication with the anode passages. The method further comprises selecting a maximum desired amount of nitrogen to be found in the fuel cell stack and calculating an actual amount of nitrogen in the fuel cell stack. Next, the method provides for comparing the maximum desired amount of nitrogen in the fuel cell stack to the actual amount of nitrogen in the fuel cell stack, and opening the valve if the actual amount of nitrogen in the fuel cell stack is greater than the maximum desired amount of nitrogen in the fuel cell stack. The method calculates the actual amount of nitrogen in the fuel cell stack based on an amount of nitrogen that enters the anode passages due to an age of the fuel cell stack.

Abstract: A fuel cell system that employs a technique for nitrogen bleeding. The fuel cell system includes a fuel cell stack having a first sub-stack and a second sub-stack, where the hydrogen gas flow is flow-shifted between the sub-stacks. A first nitrogen bleed valve is provided in an anode gas input line coupled to the first sub-stack and a second nitrogen bleed valve is provided in an anode gas input line coupled to the second sub-stack. When the first sub-stack is receiving the anode gas, and a nitrogen bleed is requested, the first bleed valve is closed and the second bleed valve is opened to provide the nitrogen bleeding. When the second sub-stack is receiving the anode gas, and a nitrogen bleed is requested, the second bleed valve is closed and the first bleed valve is opened to provide the nitrogen bleed.

Abstract: A control strategy for removing nitrogen from the anode side of a fuel cell stack. The control strategy includes using a bleed valve to remove the nitrogen during the operation of the fuel cell stack until the stack ages to a point where the bleed valve is maintained open, but the concentration of nitrogen in the anode side of the stack continues to increase. Once the concentration of nitrogen in the anode side increases to a predetermined level, then a purge valve is opened in combination with the bleed valve to reduce the concentration of nitrogen. Once the nitrogen concentration is reduced below the level, then both valves are closed, and the sequence is repeated.

Abstract: A fuel cell system that uses compressed and heated cathode input air to heat the fuel cell stack at system start-up. The system includes a heat exchanger that uses the system cooling fluid to cool the compressed and heated cathode input air before it is sent to the fuel cell stack. At system start-up, a proportional by-pass valve directs a controlled portion of the cooling fluid around the heat exchanger so that the heated cathode input air can be used to heat the fuel cell stack. Once the stack reaches its operating temperature, the by-pass valve does not by-pass the heat exchanger. The fuel cell system also includes an inlet air valve that is used to choke the compressor at system start-up to cause the compressor to rapidly heat the compressed air.

Abstract: A temperature control system and method for a fuel cell stack cooling system is disclosed. The temperature control system includes a coolant circulation line for circulating a coolant to and from a fuel cell stack. A coolant pump is provided in the coolant circulation line, and a pump ?P sensor is provided in fluid communication with the coolant circulation line on inlet and outlet sides of the coolant pump. The pump ?P sensor measures a change in pump pressure between the inlet and outlet sides of the coolant pump. A pump map is provided having correlated values of pump speed, change in pump pressure and coolant flow rate for correlating the coolant flow rate with the pump speed and the change in pump pressure to attain a desired coolant flow rate for optimum fuel stack cooling.

Abstract: The present invention is a method of operating a fuel cell stack and system that minimizes the potential for having a large pressure differential between the anode and cathode flow fields and a low relative humidity occurrence within the cathode flow fields. This is accomplished by tempering the downward transient in power demand seen by the fuel cell stack. The downward transient in power demand on the fuel cell stack is tempered by reducing the rate at which the power generated by the fuel cell stack is decreased and providing the excess power generated by the fuel cell stack to other parasitic components of the fuel cell system.