Compressor Management Strategy

The current cycle of Figs. 7.42, 7.43, and 7.44 can be utilized to verify the stack-compressor interaction in higher dynamic conditions. Figure 7.47a, b reports the results obtained with a ramp of 50 A/s and the compressor management strategy N.2 (Fig. 7.40), corresponding to a constant air flow rate of 24 Nm /h,... 

The results reported above show that the compressor management strategy adopted during the dynamic operations tested clearly affects both individual cell voltage regularity (and then stack reliability) and FCS efficiency. In fact, although... 

The key parameters to be controlled in this sub-system are air mass flow rate and pressure. Therefore, this section is focused on the characteristics of devices capable to realize useful pressure and flow rate of the oxidant feed (blowers and compressors), postponing the discussion about the integration of air supply system with the other FCS sub-systems to the successive three sections, which are dedicated to thermal and water management strategies and to overall system performance optimization. 

The Fig. 6.5 shows the relation between R and the stack power, which is used for all the tests reported in this chapter. This figure evidences that the selected air management strategy determines R values decrease from R = 9 at open circuit to about R — 2 for a stack power between 500 and 2000 kW. These values of R are specifically selected to minimize the air compressor energy losses (see Sect. 4.3). 

The results shown in previous sections suggest the crucial role of the oxidant supply system, in particular the effect of the stoichiometric ratio (air flow rate) on FCS efficiency and dynamic performance. In order to give further information about this issue, in this paragraph different air management strategies are closely examined, with particular reference to their influence on cell voltage uniformity and air compressor parasitic losses. 

The behavior of the subsystem composed by stack and air compressor is studied using four different management strategies, which allows different profiles of stoichiometric ratio versus stack current to be obtained, as discussed in the following analysis. 

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