Long breathing lean NO x trap regeneration with supplemental n -butanol

Abstract

This paper evaluates a long breathing strategy of lean NO _x trap for achieving ultra-low nitrogen oxide (NO _x ) emissions, with an aim to reduce the associated fuel penalty. The fuel impacts on the long breathing strategy of lean NO _x 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 NO _x trap strategies. For a very low engine-out NO _x emission level of ~30 ppm, the long breathing adsorption of the lean NO _x trap shows a significant improvement in NO _x storage efficiency compared to a conventional lean NO _x trap operational strategy for a moderate level of NO _x emissions. The use of n-butanol fuel in diesel engines produces much lower NO _x and particulate matter emissions, which is deemed advantageous for operating the long breathing lean NO _x trap strategy. As a reductant for lean NO _x trap regeneration, n-butanol is found to be more effective in terms of regeneration effectiveness, NO _x conversion efficiency, and potential hydrogen (H₂) 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 NO _x trap strategies. Given a low level of NO _x emissions from n-butanol combustion, the long breathing lean NO _x trap strategy can potentially achieve ultra-low NO _x emissions with a minimum fuel penalty.