Investigations of Lean NOx Trap (LNT) Regeneration Strategy for Diesel Engines

Paper #:
  • 2017-24-0124

  • 2017-09-04
To fulfil the new European real driving emissions (RDE) legislation, the LNT operation strategy – especially for DeNOx events – has to be optimized to minimize NOx as well as CO and HC emissions. On one hand the DeNOx purges should be long enough to fully regenerate the lean NOx trap, on the other hand the purges should be as short as possible to reduce the fuel consumption penalty from rich mode. Fundamental experiments have been conducted on a synthetic-gas-test-bench, purposely designed to test LNT catalysts. This methodology allowed to remove NOx from the gasfeed after the lean storage phase. The actually reduced amount of NOx could be easily calculated from the NOx storage before a regeneration minus the NOx that was desorbed during the DeNOx event and afterwards thermally desorbed NOx. To show the effect of aging method on the regeneration characteristics, tests have been performed with a in a car endurance run aged LNT and a synthetic hydrothermally aged LNT. The results show the effect of different space velocities, catalyst temperatures and DeNOx durations (as function of purge duration and purge splitting) on the DeNOx efficiency and rich gas emissions. Temperature variations indicated that both LNTs better regenerated at 300°C than at 250°C. Higher space velocities led to shorter regeneration durations than with lower space velocities. The DeNOx pulse duration was varied by DeNOx pulse splitting at a constant cumulated rich time per regeneration event. The results showed that more short pulses led to the same DeNOx efficiency as a long single purge, to lower CO and HC emissions but also to an increased dinitrogen oxide formation. By varying the purge duration with single pulses it was observed, that the regeneration efficiency was highest in the first seconds of the DeNOx. By a reduction of DeNOx pulse duration CO and HC emissions were reduced without decreasing the LNT regeneration performance.
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