Advanced Catalytic Technologies for Compressed Natural Gas – Gasoline Fuelled Engines

The main challenges of the CNG engine fuelling in terms of methane abatement in the aftertreatment system are addressed in this study by using different loaded PGM catalysts. A dual-fuel injection strategy of methane-gasoline was implemented where methane gas was port-injected into the intake in stoichiometric conditions at levels corresponding to 20 and 40% energy density replacement of gasoline fuel. High, medium, and low loaded Pd/Rh catalysts were used and compared to study the effect of PGM loading on the catalyst light-off activity for methane. Results indicate that increasing the Pd loading led to significantly earlier light-off temperatures achieved at relatively lower temperatures of 340, 350 and 395oC respectively. However, the benefit diminishes above Pd loading >142.5 g ft-3. The study has also demonstrated that NH3 is formed over the CNG catalyst due to steam-reforming reactions from the increased levels of methane in the exhaust with the dual-fuelling. Hence aftertreatment technologies such as SCR should be adopted to remove them. This further highlights the need to regulate the harmful NH3 emissions from future passenger cars fuelled with CNG. In addition, the benefits of the dual-fuel system in terms of lower engine output CO2, non-methane hydrocarbon (NMHC) and particulate matter (PM) emissions compared to the GDI mode alone are presented.