FUEL CELL SYSTEM AND ANODE OFF-GAS DISCHARGE AMOUNT ESTIMATION SYSTEM

A fuel cell system includes a fuel cell, a supply flow passage and a discharge flow passage for anode gas, a gas-liquid separator, a discharge valve, a differential pressure detection unit configured to detect a differential pressure between an upstream side and a downstream side of the discharge valve, and a control unit. The control unit is configured to estimate an effective cross-sectional area of the discharge valve for the anode off-gas, which is decreased by an amount of water flowing into the gas-liquid separator and flowing out from the discharge valve, based on the differential pressure, and to estimate a discharge amount of the anode off-gas based on the estimated effective cross-sectional area.