Exhaust fuel diluting mechanism and fuel cell system with the exhaust fuel diluting mechanism

A diluting mechanism for an exhaust fuel that dilutes the concentration of the exhaust fuel in a dilution chamber, where the exhaust fuel is exhausted from a fuel cell, the diluting mechanism comprising:

• a fuel inlet constructed to receive exhaust fuel from an anode exhaust of the fuel cell and transmit the received exhaust fuel to the dilution chamber;
• a diluent inlet provided for supplying a diluent to the dilution chamber;
• a diffusion flow path provided in the dilution chamber for mixing the exhaust fuel that is supplied from the fuel inlet with the diluent that is supplied from the diluent inlet;
• a fuel exhaust port for exhausting the diluted exhaust fuel out of the dilution chamber through the diffusion flow path;
• and
• a nozzle that narrows a flow path, provided at the fuel inlet,
• wherein the nozzle limits a supply quantity of the exhaust fuel to the dilution chamber before the exhaust fuel comes into contract with the diluent, and
• wherein when a diameter of the nozzle is d and a purge flow rate of the exhaust fuel that is exhausted from the fuel cell is Q, a relationship between the purge flow rate Q and the diameter d is set to meet formula:
• Q=πd2(2/(κ+1))1/(κ−1)×{2/(κ+1)}1/2ρv/4
• where κ is a specific heat ratio of the exhausted fuel, ρ is a density of the exhaust fuel at an upstream side of the nozzle, and v is the speed of sound.