Low-Temperature Ethanol Reforming: A Multi-Cylinder Engine Demonstration

It has been previously reported that ethanol can be reformed at around 300°C to a mixture of hydrogen, carbon monoxide, and methane using copper-plated nickel catalyst. This low reforming temperature enables heat to be supplied from the engine exhaust. Single-cylinder engine testing demonstrated that this gaseous mixture of "ethanol reformate" enhances engine combustion and part load dilution capability, which decreases fuel consumption while also reducing feedgas NO_x emissions. In addition, excellent cold start capability with significantly reduced hydrocarbon emissions was observed. Thus, ethanol reformate has the potential to address two major barriers to wider use of ethanol as an engine fuel: ethanol's low heating value per volume and higher hydrocarbon emissions at startup relative to gasoline.

In this study, the dilute capability of a multi-cylinder engine was assessed using a mixture of 50% reformate and 50% E85 on a mass basis at several key part load operating points. A strategy combining lean-burn with internal residual dilution was used to maximize thermal efficiency while maintaining adequate exhaust gas temperature for reformer operation. The resulting feedgas NO_x emissions are low enough to enable the use of a reasonably sized lean NO_x trap with low regeneration frequency for minimal impact to the fuel consumption benefit.

Cold start testing at 20°C showed that 50% reformate mass fraction is sufficient to provide significantly reduced start-up emissions and fuel consumption compared to an E85 baseline. The retarded spark timings incorporated in the test engine's production calibration enabled 300°C exhaust temperatures for three-way catalyst light-off after 15 seconds of operation. The results indicate that a reasonably sized reservoir tank could supply enough reformate for vehicle start.

While most of the results of this study were acquired using simulated ethanol reformate from gas bottles, data at one part-load engine operating point was obtained using a working prototype reformer utilizing engine exhaust heat.