Fuel cell system

Abstract

The disclosure describes fuel cell systems including a fuel cell stack that generates electricity, an exhaust valve that externally vents a fuel gas from a fuel chamber of the fuel cell stack, and a controller that computes an estimated time to replace an oxidant gas in at least the fuel chamber with a newly supplied fuel gas, wherein at a time of starting-up the fuel cell system the controller maintains the exhaust valve in an open position for the estimated time. In some embodiments, the controller computes the estimated time as a summation of a first time Tmeasured from the fuel cell start-up time to a time when contents of a supply conduit are replaced with fuel gas, a second time Tmeasured from the time when contents of a supply conduit are replaced with fuel gas to a time when contents of the fuel chamber are replaced with fuel gas, and a third time Tmeasured from the time when contents of the fuel chamber are replaced with fuel gas to a time when contents of the exhaust conduit are replaced with fuel gas. The disclosure further describes methods of operating a fuel cell system, particularly during fuel cell start-up.