Effect of hydrocarbon emissions from PCCI-type combustion on the performance of selective catalytic reduction catalysts

Core samples cut from full size commercial Fe-and Cu-zeolite SCR catalysts were exposed to a slipstream of raw engine exhaust from a 1.9-liter 4-cylinder diesel engine operating in conventional and PCCI combustion modes. Subsequently, the NOx reduction performance of the exposed catalysts was evaluated on a laboratory bench-reactor fed with simulated exhaust. The Fe-zeolite NOx conversion efficiency was significantly degraded, especially at low temperatures (<250°C), after the catalyst was exposed to the engine exhaust. The degradation of the Fe-zeolite performance was similar for both combustion modes. The Cu-zeolite was much more resistant to HC fouling than the Fe-zeolite catalyst. In the case of the Cu-zeolite, PCCI exhaust had a more significant impact than the exhaust from conventional combustion on the NOx conversion efficiency. For all cases, the clean catalyst performance was recovered after heating to 600°C. GC-MS analysis of the HCs adsorbed to the catalyst surface provided insights into the observed NOx reduction performance trends.