04

CURRENT DENSITY (A/cri)

Fig. 1 V-I characteristics obtained under different stack temperatures

55 60 65 70 75 80 I STACK TEMPERATURE CC)

Fig. 2 Relative output voltage as function of stack temperature

55 60 65 70 75 80 I STACK TEMPERATURE CC)

Fig. 2 Relative output voltage as function of stack temperature

From the data acquired on static characteristics, empirical formulas have been derived for correcting output voltage, as reproduced below. V=V3ASE+/XVCi)+^V(PH^VCr)+^V(C)+^Y(A)+^V(HC)

-0380mV/mA/cn?

( 200mA/crf < i < 400mA/cni) /? p= 57mV/kg/ca5 £t= 1.59mV/*C (T=£73t;)

= -0.69mV/"C (T>73'C) ßc=l02 (taking account of steam jSA= 49 (at 4COmA/cn5) ß^ limV/t) : 0 (T-Tc) ^12.5*0 = 9.6mV/°C : 12.5*0 < (T-Tc) ^ 25*C Cell voltage [mV] Current density [mA/cm2] Pressure [kg/cm2 abs.] Stack temperature [°C]

Molecular fraction of hydrogen '

Molecular fraction of oxygen

Dew point of cathode inlet arr [°C]

/\V(Q = £c ]n(Yo2/Yoi) = ln(YH2/YHi) •A.V(HC) = ^ u; (T-Tc)

/S : Voltage correction coefficient

1 : Reference condition.

2 : Operating point IR : Current density HC : Cathode dew point

(2) Changes of load

The 1 kW stack was used for tests covering load increase/decrease, sharp load lowering/rising, overloading, and repeated loading.

The test on sharp load lowering/rising-simulating the conditions occurring upon crash-stop astern maneuver-yielded the results reproduced in Fig. 3, where load was lowered at a rate of 18%/s and raised at 3%/s. Figure 4 shows the result of repeated loading test, in which the current was 10 times lowered from rated level down to 25% and raised again at intervals of 20s. The output power is revealed to have well followed the changes of current (i.e. of load).

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