Lean NOx trap study on a light-duty diesel engine using fast-response emission analysers

Storage and regeneration events have been studied using fast response emission analysers (~10ms) for a lean NOx trap fitted to a light-duty diesel engine. Tests were conducted at both low and high exhaust temperatures for various storage and purging periods. The use of fast response analysers has provided detailed information during the short regeneration periods and as combustion switched between rich and lean operating modes. It has also enabled quantification of the storage, reduction and overall conversion efficiencies as well as the instantaneous trapping efficiency. With exhaust temperatures of 250oC storage efficiency was low ~30%. During purging two distinct NO spikes (breakthroughs) were measured downstream of the LNT at the beginning and end of regeneration.
For this LNT the primary reducing mechanism is CO reacting with NO but CO reacting with ceria and/or water, the water-gas shift reaction, is suspected.. With exhaust temperatures of 400oC storage efficiencies were high ~80-90% except for a case of long storage/short purge when the trap was near saturation. NOx breakthrough during enrichment depended on storage and purge periods and the availability of catalyst sites. NO2 breakthrough was also observed at the end of regeneration as the combustion switched to lean operation. Generally, for the high temperature case on this LNT, the primary reducing mechanism is CO reacting with NO2