Question

When measuring the efficiency of a fuel cell vehicle, how must the auxiliary power demands be integrated into the final hydrogen consumption calculation?

Accepted Answer

To calculate the final hydrogen consumption of a fuel cell vehicle, one must account for the total electrical load, which consists of the power required for propulsion and the power required for auxiliary systems. Auxiliary power demands refer to the energy consumed by vehicle components that are not involved in moving the car, such as the air conditioning, heating, infotainment system, lighting, and the internal balance of plant components like air compressors, cooling pumps, and humidifiers required to keep the fuel cell stack operating. These auxiliary demands are integrated by summing the power consumed by these systems and adding it to the power consumed by the electric traction motor used for propulsion. The fuel cell stack must generate enough electricity to satisfy this combined total demand. Because the fuel cell is not one hundred percent efficient, it consumes hydrogen to produce this total electrical output. Therefore, the total hydrogen mass flow rate is directly proportional to the total electrical power output divided by the fuel cell efficiency at that specific load point. To determine the consumption per unit of distance, divide the total hydrogen mass consumed during a specific test cycle by the total distance traveled. Failing to include auxiliary power in the calculation results in an underestimation of hydrogen consumption, as the fuel cell must draw extra hydrogen to power these secondary systems while the vehicle is in operation.

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When measuring the efficiency of a fuel cell vehicle, how must the auxiliary power demands be integrated into the final hydrogen consumption calculation?