Influence of Exhaust Hydrogen addition and the Effects of oxygenated Fuels on a three-way Catalyst for GDI Engines

To mitigate the detrimental effects of ever increasing consumption of fossil fuels by the transport sector on urban air quality and the global climate, despite the continuous tightening of emissions legislation for road transport, necessitates further development of exhaust after-treatment systems and renewable fuels. To this end, it is vital that strategies for enhancing low temperature efficiencies of after-treatment catalysts be developed and that they can operate in synergy with the combustion of oxygenated renewable fuel blends. One such strategy is the upstream injection of hydrogen (H₂), which has shown to be effective in a lean exhaust environment but has received little attention in the context of stoichiometric GDI engine exhaust. The experimental studies in this work were carried out on a modified spark-ignition engine, equipped with hydrogen introduction and variable emission extraction capabilities to investigate commercially available after-treatment devices in a real exhaust gas environment. The system was built and commissioned for a precise H₂ addition upstream of a three-way catalyst (TWC), as well as long and short duration experiments for varying fuel blends, so as to investigate the effect of H₂ addition (H₂ levels up to 8000 ppm) and various oxygenated drop-in blends on the conversion performance of different TWC’s. Small amounts of H₂ addition showed a reduction in light-off temperature for the legislated gaseous emission species and increasing H₂ addition levels resulted in a decrease in steady-state oxidation conversion rates. H₂ was also found to decrease the time for particulate levels to reach stable conditions downstream of the TWC. A reduced light-off temperature was found with shorter oxygenated drop-in molecules, an effect which decreased with increasing chain length or complexity of the drop-in molecule. Any fuel effect on tailpipe particulate levels was inferior to the capability of the TWC to oxidise and trap small sized particles