Patent ID: 8603688

Claim:
A fuel cell system comprising: at least one fuel cell including an anode inlet and an anode outlet, said anode inlet and said anode outlet being connected by an anode recirculation line; a source of hydrogen gas providing hydrogen gas to the anode inlet; an injection device for injecting the hydrogen gas from the source to the anode inlet, said injection device producing an audible injection noise when it injects the hydrogen gas; first and second acoustic sensors located in the anode recirculation line and spaced a known distance from each other, said first and second sensors detecting the injection noise and providing a sensor signal indicative of the noise; and a controller programmed to be responsive to the sensor signals from the first and second acoustic sensors, said controller being programmed to determine the concentration of hydrogen gas in the anode recirculation line based on the time between when the controller receives the sensor signal from the first sensor and receives the sensor signal from the second sensor.