Provided is a method of controlling a fuel cell system having a fuel cell stack, a reformer configured to reform a raw fuel and supply the reformed raw fuel to the fuel cell stack, a fuel flow rate control unit configured to control a flow rate of the raw fuel supplied to the reformer, an air supply pipe configured to supply oxygen to the raw fuel, and a combustor configured to mix a cathode discharged gas and an anode discharged gas discharged from the fuel cell stack and combust the mixed gas. The method of controlling the fuel cell system includes detecting at least one of a current value generated from the fuel cell stack and an oxygen supply amount supplied from the air supply pipe; estimating a composition of the anode discharged gas on the basis of at least one of the current value and the oxygen supply amount; and controlling a temperature of the combustor by adjusting the flow rate of the raw fuel using the fuel flow rate control unit on the basis of the estimated composition of the anode discharged gas.

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.

A vehicle includes a fuel cell, an inlet valve, a purge valve, and a controller. The fuel cell has an anode side configured to receive hydrogen. The inlet valve is configured to open to deliver the hydrogen to the anode side. The purge valve is configured to open to purge water and nitrogen from the anode side. The controller is programmed to, operate the inlet valve to inject hydrogen into the anode side via opening the inlet valve followed by closing the inlet valve. The controller is further programmed to, in response to a concentration of the hydrogen in the anode side being less than threshold, open the purge valve to purge water and nitrogen from the anode side.

An exhaust duct of a fuel cell exhaust system includes a convolute duct, a resonator coupled to and in fluid communication with the convolute duct, a mid-duct coupled to and in fluid communication with the resonator, and a tail duct coupled to and in fluid communication with the mid-duct, the tail duct comprising a lower duct and an upper duct. The upper duct includes an incline duct, a transition duct, a decline duct, and a hydrogen sensor having a portion positioned within the transition duct. A first portion of an exhaust is diverted to the lower duct and a second portion of the exhaust is diverted to the upper duct and measured by the hydrogen sensor to determine hydrogen content of the exhaust.

A method for shutting down a fuel cell system (2) having at least one fuel cell (3), which fuel cell comprises an anode chamber (10) and a cathode chamber (6), wherein after the shut-down hydrogen remains in the anode chamber (10) of the fuel cell (3) in order to prevent carbon corrosion and to ensure a hydrogen protection time. The invention is characterized in that when the hydrogen in the anode chamber (10) is largely used up directly or after a specified number of subsequent meterings of hydrogen at least into the anode chamber (10), the hydrogen protection time is actively terminated by air being actively admitted into the cathode chamber (6), the fuel cell (3) being actively cooled before air is actively admitted into the cathode chamber (6).

A fuel supply control system and method for a fuel cell are disclosed. The system includes: a fuel cell configured to receive a fuel gas and an oxidation gas and generate electric power; a recirculation line configured to circulate gas containing the fuel gas and connected to a fuel electrode of the fuel cell; a discharge valve provided in the recirculation line and configured to allow the gas to be discharged to the outside when open; a discharge amount estimator configured to estimate a discharge amount of the discharged gas based on a supply amount of the fuel gas supplied to the recirculation line, a consumption amount of the fuel gas consumed in the fuel cell, and a change in the amount of the gas in the recirculation line; an offset calculator configured to calculate the discharge amount of the gas estimated by the discharge amount estimator with the discharge valve closed, as a discharge offset; and a controller configured to control opening/closing of the discharge valve.

A fuel cell system includes: a fuel cell; an anode off-gas discharge path through which an anode off-gas exhausted from an anode of the fuel cell is discharged; a heating medium circulation path through which a heating medium that recovers heat generated in the fuel cell is circulated; a heat exchanger disposed in the heating medium circulation path; an electric power converter that converts the electric power output from the fuel cell; a case that houses the electric power converter; a first air feeder that supplies air to the case; a housing that houses the fuel cell, the case, and the first air feeder; and an air discharge path through which the air having passed through the case is discharged to outside of the housing. A downstream end of the anode off-gas discharge path is connected to the air discharge path.

Provided is a method of controlling a fuel cell system having a fuel cell stack, a reformer configured to reform a raw fuel and supply the reformed raw fuel to the fuel cell stack, a fuel flow rate control unit configured to control a flow rate of the raw fuel supplied to the reformer, an air supply pipe configured to supply oxygen to the raw fuel, and a combustor configured to mix a cathode discharged gas and an anode discharged gas discharged from the fuel cell stack and combust the mixed gas. The method of controlling the fuel cell system includes detecting at least one of a current value generated from the fuel cell stack and an oxygen supply amount supplied from the air supply pipe; estimating a composition of the anode discharged gas on the basis of at least one of the current value and the oxygen supply amount; and controlling a temperature of the combustor by adjusting the flow rate of the raw fuel using the fuel flow rate control unit on the basis of the estimated composition of the anode discharged gas.

A fuel cell system includes a fuel cell in which cells are stacked, a voltage sensor that detects a voltage in unit of one or more of the cells, a control unit that determines an operating point of the fuel cell and causes the fuel cell to operate. The control unit causes the fuel cell to operate at a low efficiency operating point having a lower efficiency than an efficiency of a reference operating point in a warm-up operation. In the warm-up operation, the control unit calculates a total number of the cells in which the voltage detected by the voltage sensor is equal to or less than a predetermined first reference voltage and calculates an exhaust hydrogen concentration based on the total number or the cells.

A fuel-cell hydrogen recycling system, comprising a fuel cell; a controller; a hydrogen recycling pipeline provided with a hydrogen circulating pump and a check valve; an air inlet pipeline and an air outlet pipeline connected to the fuel cell, respectively; a hydrogen inlet pipeline provided with a hydrogen inlet valve; and a hydrogen outlet pipeline provided with a hydrogen outlet valve, with the hydrogen recycling pipeline connected to the hydrogen inlet pipeline, wherein the system further comprises a gas-liquid separating reservoir, which comprises a reservoir positioned at its upper portion and a gas-liquid separator positioned at its lower portion communicated with each other vertically, the reservoir is connected to the hydrogen outlet pipeline and the hydrogen recycling pipeline, respectively, and the gas-liquid separator discharges exhaust water and redundant nitrogen through a exhaust pipeline that is provided with a ventilation valve.