Patent ID: 7867661

Claim:
A method for scavenging a fuel cell system which comprises a fuel gas passage through which a fuel gas flows, an oxidant gas passage through which an oxidant gas flows, and a communicating passage and a communicating valve so as to selectively allow the fuel gas passage and the oxidant gas passage to communicate with each other, the method comprising the steps of: monitoring a state transition of the fuel cell after a termination of power generation; opening the communicating valve so as to open the communicating passage when a signal indicative of the state transition meets a predetermined criterion; computing an amount of an oxidant gas required for first and second scavenging according to a system shut off time between a termination of power generation by the fuel cell and a start-up of the first scavenging, wherein the amount of oxidant gas required for the first scavenging is computed to be a smaller amount as the system shut off time becomes longer; conducting the first scavenging for scavenging the oxidant gas passage with the oxidant gas as well as for diluting a remaining hydrogen gas in the fuel as passage; and conducting the second scavenging for the fuel gas passage with the oxidant gas after a termination of the first scavenging, wherein the first and second scavenging is conducted with the amount of the oxidant gas provided by the step of computing.