Analysis of the FCS Dynamic Behavior on Driving Cycles

In Fig. 6.22a, b, the acquisition versus time of stack current, voltage, and temperature is reported for one R40 and four consecutive R47 driving cycles, respectively [1]. The purge, humidification, and stoichiometric ratio control strategies described in the previous sections are used also during these tests. 

The experiments are described without taking into account the start-up issues, already analyzed in Sect. 6.4. 

In Fig. 6.23a, b, the coefficient of variation is reported as function of time for R40 and R47 driving cycles, respectively. Fast and transient excursions outside the optimal region of Fig. 6.20 occur at fuel cell system minimum power of both cycles and for the highest power peak of R40 (170 s in Fig. 6.22a). However, for R40 cycle these excursions do not involve significant losses of cell voltage uniformity, as evidenced by values of coefficient of variation always below 2% (Fig. 6.23a), indicating that the short durations of shifts from the optimal region of 

A detail of individual cell voltages for the peak at 410 s is shown in Fig. 6.24, where three instants are reported, the one just before the acceleration, the time corresponding to the maximum acceleration, and just after voltage stabilization. It is possible to observe that several cells are responsible of the Cy value higher than 4% and that all cells show a lower voltage during acceleration with respect to the stabilized values. 

This behavior seems related to the different dynamic response of stack and air compressor, as evidenced in Fig. 6.25a and b, where air flow rate and stack power 

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