Long breathing lean NOx trap regeneration with supplemental n-butanol

摘要

This paper evaluates a long breathing strategy of lean NOx trap for achieving ultra-low nitrogen oxide (NOx) emissions, with an aim to reduce the associated fuel penalty. The fuel impacts on the long breathing strategy of lean NOx trap operation are examined on a heated flow bench with diesel and n-butanol as the reductants. Engine tests are performed to identify suitable working regions for the lean NOx trap strategies. For a very low engine-out NOx emission level of similar to 30 ppm, the long breathing adsorption of the lean NOx trap shows a significant improvement in NOx storage efficiency compared to a conventional lean NOx trap operational strategy for a moderate level of NOx emissions. The use of n-butanol fuel in diesel engines produces much lower NOx and particulate matter emissions, which is deemed advantageous for operating the long breathing lean NOx trap strategy. As a reductant for lean NOx trap regeneration, n-butanol is found to be more effective in terms of regeneration effectiveness, NOx conversion efficiency, and potential hydrogen (H-2) yield compared to using diesel fuel in the after-treatment. A fuel penalty analysis is conducted for the selected cases with combinations of different combustion modes and lean NOx trap strategies. Given a low level of NOx emissions from n-butanol combustion, the long breathing lean NOx trap strategy can potentially achieve ultra-low NOx emissions with a minimum fuel penalty.