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 selective catalytic reduction catalysts were exposed to a slipstream of raw engine exhaust from a 1.9-liter 4-cylinder diesel engine operating in conventional and premixed charge compression ignition (PCCI) combustion modes. Subsequently, the NO_x reduction performance of the exposed catalysts was evaluated on a laboratory bench-reactor fed with simulated exhaust. The Fe-zeolite NO _x 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 hydrocarbon (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 NO_x conversion efficiency. For all cases, the clean catalyst performance was recovered after heating to 600°C. Gas chromatography mass spectrometry analysis of the HCs adsorbed to the catalyst surface provided insights into the observed NO_x reduction performance trends.