Transient Behavior of Methanol Steam Reformers in the Context of Automotive Fuel Cell Engine Integration

On board methanol steam reforming technology has been considered as a potential alternative to on board hydrogen storage in fuel cell vehicles. Due to the transient nature of the vehicle power demands, fuel cell engines must be capable of changing power production levels in a transient manner. If a steam reformer is integrated in a vehicular fuel cell engine, it will also be subject to these transients. This study investigates the transient response of methanol steam reformers subject to step changes in the rate of methanol fuel input. Finite element methanol steam reformer models were developed and validated using data obtained from experimental reformers at UC-Davis. The results of this study include transient and steady state reformate gas composition, as well as reformer temperature distribution. In the analysis particular attention is given to heat transfer mechanisms that promote transient variations in reformate gas CO and H2 concentrations. In addition, the effect of reformer length on transient reformate quality is studied. In general it was observed that longer reformers exhibited less of a drop in reformate hydrogen concentration when methanol flow rate was increased. However, longer reformers produced higher CO amounts than smaller reformers and were more susceptible to CO spikes during methanol flow increases.