In this paper, we discuss simulation results for a reference system design and options to increase the system efficiency, thermal and water management, rapid cold start, influence of high design ambient temperatures, and atmospheric pressure systems vs. pressurized systems. As the actual process inefficiencies are taken into account, however, the system efficiency decreases substantially. The model includes every system component that has an energy or material transport or balance aspect. Process water is used in the reformer, and for water-gas shift and reformate quenching. A significant system integration issue is the mismatch between the temperatures of the POX reactor, the water-gas shift reactors, and the fuel cell stack.
Thermal integration is achieved by the use of a steam generator and an air preheater.
The key design conditions and the controlling system variables are given in Table 1 . Half of the condenser heat load is in the form of phase change heat transfer. A high-performance system was designed based on the effects of varying several key design and operating parameters. As the POX temperature is raised, the system efficiency decreases, as shown in Fig. 2. The system efficiency is increased by increasing the cell voltage, which also decreases the heat duties at the fuel-cell stack, radiator, and condenser, as indicated in Table 5 .