Lean NO x trap study on a light-duty diesel engine using fast-response emission analysers

Abstract

Abstract

Storage and regeneration events have been studied using fast-response emission analysers (∼10 ms) for a lean NO _x trap (LNT) 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 250 °C, storage efficiency was low (∼30 per cent). 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 400 °C, storage efficiencies were high (∼80–90 per cent), except for the long-storage/short-purge case when the trap was near saturation. NO _x 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.