Water-Gas Shift Catalysts for use in D-EGR Engines
Gordon Bartley, Southwest Research Institute
As increased engine efficiency becomes necessary to meet future fuel economy and CO2 legislation, alternative combustion engines are being considered. These engines will present unique challenges and opportunities to emissions control. As such a technology, Dedicated Exhaust Gas Recirculation (D-EGR) is gaining traction as a demonstrated method for improving gasoline engine efficiency. In D-EGR, all of the exhaust from one or more cylinders is fed directly back into the intake air. Operating the EGR cylinder rich of stoichiometric results in substantial hydrogen production, which is then recirculated, along with high levels of CO and unburned hydrocarbons, to the engine. The presence of H2 has been repeatedly shown to expand the dilution limit and knock tolerance of an SI engine, resulting in the potential for significant (> 15%) improvement in BTE. The limiting factor in producing H2 in this manner is the dilution tolerance of the dedicated cylinder, which is running with 25% EGR and rich. Since the beneficial effects of H2 increase monotonically with its concentration, alternative methods to increase the H2 concentration in the EGR are required. One solution is to convert the residual CO and water in the D-EGR exhaust into further H2. This can be achieved in the water-gas shift reaction (WGS) using a WGS catalyst. This work characterized a catalyst used as a WGS catalyst, and improved the formulation to achieve higher levels of WGS activity and especially H2 production under D-EGR conditions.