The major alternatives for producing work from fuel energy include combustion systems and fuel cells. Combustion systems are subject to several performance-limiting constraints. Key amongst these is the fact that combustion is an uncontrolled chemical reaction and is typically highly irreversible. The requirement to operate below the metallurgical limit adds to the irreversibility of practical combustion systems. Furthermore, the use of heat exchangers, which must have finite temperature differences between fluid streams, compounds the exergy consumption. The fuel cell conversion system is a major alternative to combustion systems. It operates as a direct conversion device and is often cited as having a potential for 100% second-law efficiency. Realistically, however, the chemical reactions involved are not reversible. More importantly, the available fuel resources must be reformed to make the chemical energy of the fuel convertible to work. The significant exergy input required must be factored into the determination of the overall exergy conversion efficiency attainable. This paper gives a simplified first- and second-law analysis for the limits of efficiency of these alternate systems for the conversion of fuel exergy to mechanical work, thus providing a more realistic comparison of the potential of both systems.

1.
Oniciu
,
L.
, 1976,
Fuel Cells
,
Abacus Press
,
Tunbridge Wells, Kent, England
, pp.
79
136
.
2.
Curzon
,
F. L.
, and
Ahlborn
,
B.
, 1975, “
Efficiency of a Carnot Engine at Maximum Power
,”
Am. J. Phys.
0002-9505,
43
, pp.
22
24
.
3.
Bejan
,
A.
, 1988, “
Theory of Heat Transfer-Irreversible Power Plants
,”
Int. J. Heat Mass Transfer
0017-9310,
31
, pp.
1211
1219
.
4.
Wilson
,
S. S.
, and
Radwan
,
M. S.
, 1977, “
Appropriate Thermodynamics for Heat Engine Analysis and Design
,”
Int. J. Mech. Eng. Educ.
,
5
(
1
), pp.
68
80
.
5.
Kalina
,
A. I.
, 1984, “
Combined-Cycle System With Novel Bottoming Cycle
,”
ASME J. Eng. Gas Turbines Power
0742-4795,
106
, pp.
737
742
.
6.
Angrist
,
S. W.
, 1971,
Direct Energy Conversion
,
2nd ed.
,
Allyn and Bacon
,
Boston
, pp.
368
386
.
7.
Hart
,
A. B.
, and
Womack
,
G. J.
, 1967,
Fuel Cells: Theory and Application
,
Chapman and Hall
,
London, England
, pp.
44
48
.
8.
Wilemski
,
G.
, 1980, “
Nonequilibrium Thermodynamics of Fuel Cells: Heat Release Mechanisms and Voltage
,”
J. Chem. Phys.
0021-9606,
72
(
1
), pp.
369
377
.
9.
Lariminie
,
J.
, and
Dicks
,
A.
, 2003,
Fuel Cell Systems Explained
,
2nd ed.
,
John Wiley & Sons
,
New York
.
10.
Hirschenhofer
,
J. H.
,
Stauffer
,
D. B.
,
Engleman
,
R. R.
, and
Klett
,
M. G.
, 1998,
Fuel Cell Handbook
,
4th ed.
, Report No. DOE/FETC-99/1076,
U.S. Department of Energy
,
Morgantown
.
11.
Adebiyi
,
G. A.
, 2003, “
Limits of Performance for Alternate Fuel Energy to Mechanical Work Conversion Systems
,” in
Proceedings of IMECE ’03
, Washington, D.C., Nov. 15–21, Paper No. IMECE2003–41285.
12.
Russell
,
L. D.
, and
Adebiyi
,
G. A.
, 1993,
Classical Thermodynamics
,
Oxford University Press
,
New York
, pp.
614
,
702
.
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