Fuel supply unit for a fuel cell system, fuel cell system and method for monitoring a fuel supply unit

An aircraft and fuel cell system comprising:

• an aircraft having a pressure storage fuel tank configured to store fuel under elevated pressure which is disposed within a pressurized region of the aircraft, wherein the pressurized region is characterized by a pressure that develops internal to the region at a level irrespective of an internal pressure of the pressure storage fuel tank;
• a safety line which connects the pressure storage fuel tank to an unpressurized region of the aircraft and/or the outer atmosphere;
• a fuel cell installed in the aircraft and having an inlet structured to receive fuel from the pressure storage fuel tank, the fuel cell also having and an anode outlet;
• a feed line that fluidly connects the pressure storage fuel tank to the fuel cell via the inlet;
• a connecting line between the feed line to the fuel cell and the safety line from the pressure storage fuel tank;
• a recirculation line disposed between the anode outlet and the inlet of the fuel cell and structured to return exhaust from the anode outlet to the inlet;
• a removal line configured to deliver exhaust from the anode outlet of the fuel cell to the unpressurised region of the aircraft and/or the outer atmosphere;
• a first pressure relief valve disposed in the removal line and connecting the anode outlet of the fuel cell to the unpressurized region of the aircraft and/or outer atmosphere via the removal line and the safety line when a pressure in the removal line exceeds a threshold;
• a second pressure relief valve disposed in the safety line between the pressure storage fuel tank and the unpressurized region of the aircraft and/or the outer atmosphere, wherein the second pressure relief valve is structured to discourage flow of fluid therethrough at a first position and relieve pressure and thereby permit flow of fluid therethrough at a second position;
• a third pressure relief valve disposed in the connecting line to permit fluid communication from the feed line to the safety line;
• a sensor for detecting an electrical voltage in the fuel cell;
• and
• an electronic control unit which is adapted to receive signals output from the sensor and which is adapted to detect a fault caused by an unintentional opening or a failure of the tank isolation valve based on the sensor signals, when in a quiescent operational state of the fuel cell system electrical energy is generated by the fuel cell.