Patent ID: 8722268

Claim:
A fuel cell system comprising: a fuel cell which includes a fuel gas channel and an oxidizer gas channel and generates electricity by using fuel gas supplied to the fuel gas channel and oxidizer gas supplied to the oxidizer gas channel; an electricity generation status detecting unit which detects an average cell voltage or a lowest cell voltage of the fuel cell, and compares the average cell voltage or the lowest cell voltage with a threshold value to detect electricity generation status of the fuel cell; a fuel gas supply unit which supplies the fuel gas; a fuel gas supply channel which connects the fuel gas supply unit and an inlet of the fuel gas channel; an ejector which is attached to the fuel gas supply channel; a fuel off-gas channel which connects an outlet of the fuel gas channel and the ejector; a discharge valve which is connected to the fuel off-gas channel and is opened for discharging gas in the fuel off-gas channel to the outside; an oxidizer gas supply unit which supplies the oxidizer gas; an oxidizer gas supply channel which connects the oxidizer gas supply unit and an inlet of the oxidizer gas channel; a pressure control unit which controls pressure of the oxidizer gas in the oxidizer gas channel; a pilot pressure input channel which branches off from the oxidizer gas supply channel and inputs the pressure of the oxidizer gas to the ejector as pilot pressure; and a control unit programmed to control the discharge valve and the pressure control unit, wherein: the ejector includes a nozzle which ejects the fuel gas supplied from the fuel gas supply unit, a needle which is placed coaxially with the nozzle, a diffuser in which the fuel gas ejected from the nozzle and fuel off-gas from the fuel off-gas channel are mixed together, and a pressure control mechanism which increases the ejector's secondary-side pressure by increasing area of the nozzle's ejecting hole while keeping the needle in a fixed position relative to the ejector when the pilot pressure input from the pilot pressure input channel rises, the pressure control mechanism including a diaphragm which abuts the nozzle, and when the average cell voltage or the lowest cell voltage detected by the electricity generation status detecting unit is equal to or less than the threshold value, the control unit opens the discharge valve after raising the pressure of the oxidizer gas and the pilot pressure by using the pressure control unit.