Various embodiments of the present application are directed to methods of measuring a mass flow rate of at least one exhaust gas constituent in an exhaust gas of a fuel cell. In one example embodiment, the method includes the steps of measuring a volumetric flow rate of the exhaust gas; using a gas sensor to determine a concentration of the at least one exhaust gas constituent, and calculating the mass flow rate of the exhaust gas constituent using the volumetric flow rate of the exhaust gas and the determine concentration of the at least one exhaust gas constituent.

A reforming element for a molten carbonate fuel cell stack and corresponding methods are provided that can reduce or minimize temperature differences within the fuel cell stack when operating the fuel cell stack with enhanced CO.sub.2 utilization. The reforming element can include at least one surface with a reforming catalyst deposited on the surface. A difference between the minimum and maximum reforming catalyst density and/or activity on a first portion of the at least one surface can be 20% to 75%, with the highest catalyst densities and/or activities being in proximity to the side of the fuel cell stack corresponding to at least one of the anode inlet and the cathode inlet.

To precisely measure and control the amount of a cathode gas supplied to a fuel cell, a fuel cell system includes a fuel cell, a first flow passage through which a cathode gas is supplied to the fuel cell, a second flow passage through which a cathode off-gas is discharged from the fuel cell, a bypass flow passage which is bifurcated from the first flow passage and which is connected to the second flow passage, a compressor provided in the first flow passage, a first flowmeter provided in the first flow passage, a flow amount regulation valve provided in the bypass flow passage, a second flowmeter provided in the bypass flow passage, and a controller which controls the flow amount of the cathode gas supplied to the fuel cell, wherein the compressor is arranged on the upstream side of the bypass flow passage, the first flowmeter is arranged on the upstream side of the compressor, the second flowmeter is arranged on the downstream side of the flow amount regulation valve, and the controller controls the flow amount of the cathode gas supplied to the fuel cell based on the flow amount measured by the first flowmeter and the flow amount measured by the second flowmeter.

A fuel cell vehicle includes a bypass valve positioned downstream of a compressor and upstream of a fuel cell stack to selectively direct airflow from the compressor to an exhaust bypassing the fuel cell in an attempt to clear a partially or fully obstructed exhaust pipe. The bypass valve may be opened by a controller when an exhaust throttle valve is at or near a wide-open throttle position. The controller may also increase compressor flow and adjust airflow to the fuel cell stack until compressor pressure, speed, or temperature exceed corresponding limits.

A fuel cell system includes: an upstream side flow path forming a flow path from an oxidation gas supply apparatus toward a fuel cell; and a downstream side flow path forming a flow path from the fuel cell toward an atmosphere. The fuel cell system includes: an oxidation gas pressure sensor that measures a pressure inside the upstream side flow path; and a controller that can execute a water content estimation mode of estimating a water content in an oxidation gas flow path including the fuel cell. The controller includes: a water content calculation unit that calculates the water content in the oxidation gas flow path including the fuel cell on a basis of an oxidation gas flow rate and an oxidation gas pressure loss.

A fuel cell system includes: a fuel cell; a first valve device provided at an oxidation gas supply channel; a second valve device provided at an oxidation off-gas discharge channel; a third valve device provided at a bypass channel; an abnormality detection unit configured to detect an abnormality; and a control unit. The control unit causes the fuel cell to initiate fail-safe power generation if (i) a different abnormality from a valve opening abnormality is detected in the first valve device, (ii) the different abnormality is detected in the second valve device, or (iii) any abnormality is detected in the third valve device. During the fail-safe power generation, if any abnormality is additionally detected in any valve device different from the valve device in which an abnormality is already detected, the control unit stops power generation by the fuel cell.

An air supply control method of a fuel cell is provided. The method includes adjusting an opening of a pressure control valve in accordance with an opening map stored in advance. The pressure control valve is disposed at an outlet of a fuel cell of an air supply line for supplying air to the fuel cell and discharging air and adjusts air pressure in the air supply line. The method further includes determining whether an air pressure state of the air supply line is normal after adjusting the opening of the pressure control valve and operating the pressure control valve at a predetermined opening in response determining that the air pressure state of the air supply line is abnormal.

A fuel cell system includes a target pressure value for the pressure in a fuel cell is set depending on a demand output value to the fuel cell. A turbine retains a set pressure line representing a relationship between an airflow rate supplied to the turbine and a pressure ratio corresponding to a ratio of a pressure upstream of the turbine and a pressure downstream of the turbine. A controller executes a first control when the target pressure value for the fuel cell is lower than the set pressure line and executes a second control when the target pressure value for the fuel cell is higher than the set pressure line. The controller controls an outlet valve so as not to be fully opened when a turbine bypass valve is fully closed.

A fuel cell system includes a fuel cell, a supply device configured to supply a cathode gas to the fuel cell; and a control unit configured to execute recovery processing of causing a catalyst of the fuel cell to recover from performance deterioration by lowering an output voltage of the fuel cell. The control unit is configured to, when the recovery processing that has been executed is completed, control the supply device to place the fuel cell in a power generation paused state while making a stoichiometric ratio of the cathode gas lower than a stoichiometric ratio of the cathode gas in a normal operation state that is a state before execution of the recovery processing.

A method of operating an aircraft includes providing a fuel cell system to power the aircraft, providing an airflow path through the fuel cell system, sensing a change mass air flow rate supplied to a compressor of the fuel cell system, and at least one of adjusting a restriction of airflow entering the airflow path in response to the sensed change in mass air flow rate, adjusting a restriction of airflow exiting the airflow path in response to the sensed change in mass air flow rate, and adjusting an air scoop to gather a different amount of air into the airflow path. A method of operating an aircraft includes sensing a change in ambient pressure supplied to an airflow path and adjusting a restriction of airflow exiting the airflow path in response to a sensed change in ambient pressure.