System for purging non-fuel material from fuel cell anodes

Abstract

A fuel cell gas purge system is provided that includes at least one fuel cell, such as a fuel cell stack or a fuel cell array, a fuel supply, and an adjustable fuel cell current load. The system further includes at least one passive purge valve disposed to purge accumulated non-fuel matter in the fuel cell, and operates according to a pressure differential across the valve. The valve can be a passive bi-directional valve, such as a dome valve, or a passive unidirectional valve. Further included is a purge management module that has a purge request module to determine when to increase the pressure of the hydrogen fuel to initiate the purge, and a purge complete module to determine when to adjust the pressure of the hydrogen fuel to complete the purge. The non-fuel matter can include non-fuel gases or condensed water.

What is claimed: 
     
         1 . A method of purging a fuel cell system, the fuel cell system including a fuel supply, a fuel cell that receives fuel from the fuel supply at a fuel flow rate, a purge valve, and an adjustable load that applies a load on the fuel cell system, the method comprising:
 detecting a purge event; and   in response to detecting the purge event, reducing the load on the fuel cell system to increase the system pressure and purge the system.   
     
     
         2 . The method of  claim 1 , wherein purging the system further comprises keeping the fuel flow rate constant before and during the purge. 
     
     
         3 . The method of  claim 1 , wherein reducing the load on the fuel cell system comprises adjusting an amount of power drawn from the fuel cell system by the adjustable load. 
     
     
         4 . The method of  claim 3 , wherein adjusting an amount of power drawn from the fuel cell system by the adjustable load comprises adjusting a charging current of a battery with a battery charger circuit electrically connected to the battery. 
     
     
         5 . The method of  claim 1 , wherein reducing the load on the fuel cell system comprises reducing the load on the fuel cell system to increase the system pressure beyond a cracking pressure of the purge valve. 
     
     
         6 . The method of  claim 1 , wherein a cracking pressure of the purge valve is approximately 1 PSI. 
     
     
         7 . The method of  claim 1 , wherein detecting a purge event comprises sensing a drop in a voltage of the fuel cell below a predetermined voltage threshold. 
     
     
         8 . The method of  claim 7 , wherein the fuel cell is a fuel cell most proximal to the purge valve within a fuel cell stack. 
     
     
         9 . The method of  claim 1 , further comprising:
 detecting a purge completion event; and   in response to detecting the purge completion event, increasing the load on the fuel cell system to decrease the system pressure and cease the purge.   
     
     
         10 . The method of  claim 9 , wherein detecting the purge completion event comprises sensing a purge stream composition comprising fuel above a predetermined fuel threshold. 
     
     
         11 . The method of  claim 10 , wherein detecting the purge completion event comprises directing the purge stream across a cathode of a second fuel cell in an array of said fuel cells, wherein sensing a purge stream composition comprising fuel above a predetermined fuel threshold comprises sensing a voltage of the second fuel cell dropping below a threshold voltage. 
     
     
         12 . The method of  claim 10 , wherein detecting the purge completion event comprises directing the purge stream over a catalyst bed in the presence of ambient air, wherein sensing a purge stream composition comprising fuel above a predetermined fuel threshold comprises sensing when a temperature of the catalyst bed exceeds a threshold level. 
     
     
         13 . The method of  claim 12 , wherein directing the purge stream over a catalyst bed comprises directing the purge stream over a bed comprising platinum. 
     
     
         14 . The method of  claim 10 , wherein detecting the purge completion event comprises directing the purge stream over an anode of an auxiliary fuel cell, wherein sensing a purge stream composition comprising fuel above a predetermined fuel threshold comprises sensing an output of the auxiliary fuel cell exceeding a threshold level, wherein said output comprises a current or a voltage. 
     
     
         15 . The method of  claim 9 , wherein detecting the purge completion event comprises detecting that a threshold time duration has been reached with a timer. 
     
     
         16 . The method of  claim 15 , wherein the threshold time duration is determined based on a current load in the fuel cell before said purge was initiated. 
     
     
         17 . A method of purging a fuel cell system, the fuel cell system including a fuel supply, a fuel cell that receives fuel from the fuel supply at a fuel flow rate, a purge valve, and an adjustable load that applies a load on the fuel cell system, the method comprising:
 detecting a purge event;   in response to detecting the purge event, reducing the load on the fuel cell system to increase the system pressure and purge the system;   detecting a purge completion event; and   in response to detecting the purge completion event, increasing the load on the fuel cell system to decrease the system pressure and cease the purge.   
     
     
         18 . The method of  claim 17 , wherein reducing the load on the fuel cell system comprises reducing an amount of power drawn from the fuel cell system by the adjustable load, and increasing the load on the fuel cell system comprises increasing the amount of power drawn from the fuel cell system by the adjustable load. 
     
     
         19 . The method of  claim 17 , wherein reducing the load on the fuel cell system comprises reducing the load on the fuel cell system to increase the system pressure beyond a cracking pressure of the purge valve. 
     
     
         20 . The method of  claim 17 , wherein detecting the purge event comprises sensing a drop in a voltage of the fuel cell below a predetermined voltage threshold, and detecting a purge completion event comprises detecting that a threshold time duration has been reached with a timer.