Energy and hydrogen consumption evaluation of a fuel cell city bus based on roller chassis dynamometer measurements

An unmodified series-production fuel cell city bus is measured on a heavy-duty roller chassis dynamometer. The two main research questions are.

•The development and comparison of different methods to measure hydrogen consumption without the use of special measuring instruments (the bus should not be modified).

•The influence of the heating, ventilation and air conditioning (HVAC) system on the fuel consumption of the bus.

For the measurements we use a heavy-duty roller chassis dynamometer. Four different transient driving cycles are selected to represent typical city bus driving patterns. The ambient temperature is controlled within certain limits to simulate different weather conditions. Different HVAC settings and simulated passenger numbers are also used to imply variation in HVAC energy consumption.
Three different methods to measure the hydrogen consumption of the bus are evaluated. They are based on the measurement of fuel cell current (A), hydrogen storage pressure (B) and product water mass (C). The methods are compared with each other and with the consumption reported by the vehicle. Based on the available validation options, we conclude that methods A and B give the most reliable results. Both show a difference of less than ±5 % for the majority of the results.
The measured hydrogen consumption (method A) is between 5 and 8 kg/100 km depending on the cycle. The efficiency of the fuel cell system is measured to be between 58 % and 50 % at low and high load, respectively, with the BoP responsible for up to 5 % point loss.
We also find that a full bus requires almost 30 % more traction power and that the heat dissipation from the passengers has a significant impact on the HVAC system. Different settings of the HVAC system are responsible for an increase in fuel consumption of up to 15 %.