Fuel processors for automotive fuel cell systems: a parametric analysis

An autothermally-reformed, gasoline-fueled automotive polymer electrolyte f uel cell (PEFC) system has been modeled and analyzed for the fuel processor and total system performance. The purpose of the study is to identify the influence of various operating parameters on the system performance and to investigate related tradeoff scenarios. Results of steady-state analyses at the design rated power level are presented and discussed. The effects of t he following parameters are included in the analysis: operating pressure (3 and 1 atm), reforming temperature (1000-1300 K), water-to-fuel and air-to- fuel reactant feed ratios, electrochemical fuel utilization, and thermal in tegration of the fuel processor and the fuel cell stack subsystems. The ana lyses are also used to evaluate the impact of those parameters on the conce ntrations of methane and carbon monoxide in the processed reformate. Both o f these gases can be reduced to low levels with adequate water-to-carbon us ed in the fuel processor. Since these two species represent corresponding a mounts of hydrogen that would not be available for electrochemical oxidatio n in the fuel cell stack, it is important to maintain them at low levels. S ubject to the assumptions used in the analyses, particularly that of thermo dynamic equilibrium, it was determined that reforming temperatures of 1100 K, a water-to-carbon mole ratio of 1.5-2.5, and the use of fuel cell exhaus t energy in the fuel processor subsystem can yield fuel processor efficienc ies of 82-84%, and total system efficiencies of 40-42% can be achieved. For the atmospheric pressure system, if the exhaust energy is not used in the fuel processor subsystem, the fuel processor efficiency would drop to 75-82 % and the total system efficiency would drop below 40%. At higher reforming temperatures, say 1300 K, the fuel processor efficiency would decrease to 78%, and the total system efficiency would drop below 39%, even with the us e of the fuel cell stack exhaust energy. (C) 2001 Elsevier Science B.V. All rights reserved.