Lambda sensing with a fuel cell stack

• US 20030203253A1
• Filed: 04/30/2002
• Published: 10/30/2003
• Est. Priority Date: 04/30/2002
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations Incorporated (General Motors Company)
• Inventors: Clingerman, Bruce J., Rock, Jeffrey A.
• Granted Patent: US 6,893,756 B2
• Time in Patent Office: Days
• US Class Current: 429/22
• CPC Class Codes: H01M 8/0258 characterised by the configuration of channels, e.g. by the flow field of the reactant or coolant
• CPC Class Codes: H01M 8/0267 having heating or cooling means, e.g. heaters or coolant flow channels
• CPC Class Codes: H01M 8/04552 of the individual fuel cell
• CPC Class Codes: H01M 8/04559 of fuel cell stacks
• CPC Class Codes: H01M 8/04753 of fuel cell reactants
• CPC Class Codes: H01M 8/242 comprising framed electrodes or intermediary frame-like gaskets H01M8/2425, H01M8/244 take precedence
• CPC Class Codes: H01M 8/2484 characterised by external manifolds
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A sensor for monitoring the lambda of a component of a reactant feed stream flowing through a fuel cell stack. The sensor comprises one or more fuel cells that are sensitive to a change in lambda of a specific component of a reactant feed stream flowing through the fuel cell. The sensitivity of the fuel cell causes a voltage produced by the lambda sensing fuel cell to vary in response to variation in the lambda of the specific component. The variation of the voltage output can be modeled and/or compared to empirical data to correlate the voltage output to the lambda of the specific component. Based on the lambda of the specific component, the operation of the fuel cell stack can be optimized.

Claims

1. A fuel cell assembly receiving reactant flows and generating an electric current therefrom, the fuel cell assembly comprising:

a plurality of fuel cells arranged in a stacked configuration with said plurality of fuel cells electrically in series, a first fuel cell of said plurality of fuel cells having a voltage output that changes in a known manner in response to changes in lambda of a first reactant flow;

a voltage monitoring device monitoring said voltage output of said first fuel cell; and

a controller that receives a signal from said voltage monitoring device corresponding to said voltage output of said first fuel cell, said controller controlling said first reactant flow in response to said signal.

2. The fuel cell assembly of claim 1, wherein said controller includes a microprocessor that compares said voltage output of said first fuel cell to a library of stored voltage outputs and adjusts said first reactant flow in response to said comparison.

3. The fuel cell assembly of claim 2, wherein said library is a compilation of expected voltage outputs for various operating conditions of said fuel cell stack and lambdas of said first reactant flow.

4. The fuel cell assembly of claim 1, further comprising a second fuel cell of said plurality of fuel cells having a second voltage output that changes in a known manner in response to changes in a lambda of a second reactant flow, said voltage monitoring device monitoring said second voltage output of said second fuel cell.

5. The fuel cell assembly of claim 4, wherein said first reactant flow is a fuel flow and said second reactant flow is an oxidant flow.

6. The fuel cell assembly of claim 1, wherein said first reactant flow is a fuel flow.

7. The fuel cell assembly of claim 1, wherein said first reactant flow is an oxidant flow.

8. The fuel cell assembly of claim 1, wherein said first fuel cell is a cluster of fuel cells having a voltage output that changes in a known manner in response to a change in lambda of said first reactant flow and said voltage monitoring device monitors said voltage output of said cluster of fuel cells.

9. The fuel cell assembly of claim 1, wherein said first fuel cell is a plurality of fuel cells that each have a voltage output that changes in a known manner in response to a change in a lambda of said first reactant flow, and said voltage monitoring device monitors said voltage output of each of said plurality of fuel cells having said voltage output that changes in said known manner.

10. The fuel cell assembly of claim 1, wherein said first fuel cell is fabricated to have a voltage output that changes in a known manner in response to changes to said lambda of said first reactant flow.

11. The fuel cell assembly of claim 10, wherein said first fuel cell is fabricated with a first reactant flow channel that is more restrictive than first reactant flow channels of said plurality of fuel cells so that said voltage output of said first fuel cell is more sensitive to changes in lambda of said first reactant flow than voltage outputs of said plurality of fuel cells.

12. The fuel cell assembly of claim 10, wherein said first fuel cell is fabricated with a first reactant diffusion media that is more restrictive than first reactant diffusion medias of said plurality of fuel cells so that said voltage output of said first fuel cell is more sensitive to changes in lambda of said first reactant flow than voltage outputs of said plurality of fuel cells.

13. The fuel cell assembly of claim 10, wherein said first fuel cell is fabricated with a first reactant primary current collector that is more restrictive than first reactant primary current collectors of said plurality of fuel cells so that said voltage output of said first fuel cell is more sensitive to changes in lambda of said first reactant flow than voltage outputs of said plurality of fuel cells.

14. The fuel cell assembly of claim 10, wherein said first fuel cell is fabricated with coolant passageways that are larger than coolant passageways of said plurality of fuel cells so that said voltage output of said first fuel cell is more sensitive to flooding of said stack than voltage outputs of said plurality of fuel cells.

15. The fuel cell assembly of claim 1, wherein said first fuel cell is selected from said plurality of fuel cells based on testing each fuel cell of said plurality of fuel cells for voltage output that changes in a predetermined manner in response to changes in said lambda of said first reactant flow.

16. A method of monitoring changes in a lambda of a reactant feed stream to a fuel cell stack comprised of a plurality of fuel cells arranged electrically in series, the method comprising the steps of:

supplying a first reactant feed stream to a fuel cell stack;

supplying a second reactant feed stream to said fuel cell stack;

selecting a first fuel cell in said fuel cell stack having a voltage output that varies in a known manner to a change in lambda of said first reactant feed stream;

monitoring said voltage output of said first fuel cell; and

controlling said first reactant feed stream based on said voltage output of said first fuel cell.

17. The method of claim 16, wherein said step of monitoring includes comparing said voltage output of said first fuel cell to a library of stored voltage outputs, and said step of controlling includes adjusting said first reactant stream based on said comparison.

18. The method of claim 17, wherein said library is a compilation of expected voltage outputs for various operating conditions of said fuel cell stack and changes in said lambda of said first reactant stream.

19. The method of claim 18, wherein said compilation of expected voltage outputs is based on modeling said first fuel cell.

20. The method of claim 18, wherein said compilation of expected voltage outputs is based on testing said first fuel cell.

21. The method of claim 16, further comprising the steps of:

selecting a second fuel cell in said fuel cell stack having a voltage output that varies in a known manner to changes in a lambda of said second reactant feed stream;

monitoring said voltage output of said second fuel cell; and

controlling said second reactant feed stream based on said voltage output of said second fuel cell.

22. The method of claim 21, wherein said first reactant feed stream is a fuel feed stream and said second reactant feed stream is an oxidant feed stream.

23. The method of claim 16, further comprising the steps of:

selecting a second fuel cell in said fuel cell stack having a voltage output that varies in a known manner to changes in said lambda of said first feed stream;

monitoring said voltage output of said second fuel cell; and

controlling said first reactant feed stream based on at least one of said voltage outputs of said first and second fuel cells.

24. The method of claim 16, further comprising the steps of:

selecting a cluster of fuel cells having a voltage output that varies in a known manner to changes in a lambda of said first reactant feed stream;

monitoring said voltage output of said cluster of fuel cells; and

controlling said first reactant feed stream based on said voltage output of said cluster of fuel cells.

25. The method of claim 16, wherein said first reactant feed stream is a fuel feed stream.

26. The method of claim 16, wherein said first reactant feed stream is an oxidant feed stream.

27. The method of claim 16, wherein said step of selecting said first fuel cell includes testing each fuel cell of the plurality of fuel cells that comprise the fuel cell stack to determine a voltage output variance for each cell in response to variances in said lambda of said first reactant stream and selecting said first fuel cell based on said testing.

28. The method of claim 16, wherein said step of selecting said first fuel cell includes fabricating said first fuel cell to have a voltage output that varies in a known manner to changes in said lambda of said first reactant flow.

29. A method of making a sensor to monitor a lambda of a reactant feed stream to a fuel cell stack comprising the steps of:

(a) supplying first and second reactant feed streams to a fuel cell;

(b) generating a voltage output with said fuel cell from said first and second reactant feed streams;

(c) monitoring said voltage output of said fuel cell;

(d) varying a lambda of said first reactant feed stream;

(e) determining a sensitivity of said fuel cell to variation of said lambda of said first reactant feed stream; and

(f) selecting said fuel cell as a sensor fuel cell when said fuel cell has a desired sensitivity characteristic to said lambda of said first reactant feed stream.

30. The method of claim 29, wherein said step of determining a sensitivity includes calculating a change in said voltage output of said fuel cell in response to variation of said lambda of said first reactant feed stream.

31. The method of claim 30, wherein said step of selecting includes comparing said change in said voltage output of said fuel cell to an average change in voltage output of other fuel cells in response to a same variation of said lambda of said first reactant feed stream.

32. The method of claim 31, further comprising the step of:

collecting empirical data on said sensitivity of said fuel cell by repeatedly performing steps (d) and (e).

33. The method of claim 32, further comprising the step of:

changing an operating condition of said fuel cell then repeatedly performing steps (e) and (f) to collect empirical data on said sensitivity of said fuel cell for said operating condition of said fuel cell.

34. The method of claim 32, further comprising the step of:

generating a library of reference voltages from said empirical data to use with said first fuel cell to monitor said lambda of said first reactant feed stream.

35. The method of claim 32, further comprising the step of:

generating an equation from said empirical data that models said voltage output of said fuel cell as a function of said lambda.

36. The method of claim 29, further comprising the steps of:

supplying said first and second reactant feed streams to a cluster of fuel cells;

generating a voltage output with said cluster of fuel cells from said first and second reactant feed streams;

monitoring said voltage output of said cluster of fuel cells;

varying said lambda of said first reactant feed stream;

determining a sensitivity of said cluster of fuel cells to variation of said lambda of said first reactant feed stream; and

selecting said cluster of fuel cells as a sensor cluster of fuel cells when said cluster of fuel cells has a desired sensitivity characteristic to said lambda of said first reactant feed stream.

37. The method of claim 29, further comprising the steps of:

supplying said first and second reactant feed streams to a fuel cell stack comprised of a plurality of fuel cells arranged electrically in series;

generating a voltage output with each fuel cell of said stack from said first and second reactant feed streams;

monitoring said voltage output of each fuel cell of said stack;

varying said lambda of said first reactant feed stream;

determining a sensitivity of each fuel cell of said stack to variation of said lambda of said first reactant feed stream; and

selecting a sensor fuel cell having a desired sensitivity characteristic to said lambda of said first reactant feed stream in said fuel cell stack.

38. The method of claim 29, wherein said first reactant feed stream is a fuel feed stream.

39. The method of claim 29, wherein said first reactant feed stream is an oxidant feed stream.