Reforming of Ethanol with Exhaust Heat at Automotive Scale

Abstract

A low-temperature ethanol-reforming pathway, catalyzed by copper–nickel powder catalysts, transforms ethanol into a mixture of H2, CO, and CH4 at temperatures between 300 and 350 °C. Blending 25–50% of this gas mixture, known as “low-temperature ethanol reformate”, with ethanol or E85 fuels, enables dilute engine operation, resulting in substantial improvements in fuel economy and emissions. It is thermodynamically feasible to drive low-temperature reforming with exhaust heat, but this requires an onboard reformer providing adequate heat exchange between exhaust and fuel while retaining the catalyst. Three low-temperature ethanol reformer architectures (representing a design evolution) were developed and tested at automotive scale with exhaust from a V8 engine. The best catalyst retention and heat-transfer properties were achieved by embedding the catalyst in fibrous metal media with a density gradient. Longitudinal shell-and-tube and finned tube reformers achieved effective heat transfer and adequate initial conversion but proved inadequate for vehicular applications because of high thermal mass, catalyst settling, and unacceptable pressure build. A transverse shell-and-tube design in which banks of parallel, vertical catalyst tubes extended through a transverse stack of exhaust-side heat-exchange plates exhibited sustained high conversion with low and stable fuel-side pressure throughout a 500 h test period. This design has relatively low thermal mass and can be readily packaged on a vehicle. Thus, onboard reforming of ethanol- or methanol-rich fuels appears to be a feasible pathway to improve fuel economy and emissions in light-duty vehicles.