The reduction of NOx in exhaust gas has been a major challenge
in diesel engine development. For the NOx reduction issues, a new
Lean NOx Catalyst (LNC) aftertreatment system has been developed by
Honda. A feature of the LNC system is the method that is used to
reduce NOx through an NH₃-Selective Catalytic Reduction (NH₃-SCR).
In an LNC system NOx is adsorbed at lean conditions, then converted
to NH₃ at rich conditions and subsequently reduced in the next lean
phase.
In recent years, as the efficiency of the diesel engine has
improved, the exhaust gas temperatures have been reduced gradually.
Therefore, the aftertreatment system needs to be able to purify NOx
at lower temperatures. The development of a new LNC which has a
high activity at low temperature has been carried out. For the
improvement of the LNC three material improvements were developed.
The first of these was the development of a NOx adsorbent which is
matching the targeted exhaust gas temperatures. The second
improvement was the development of a layer configuration to reduce
the negative cross-effects of NOx adsorbent and zeolite at low
temperature. The final improvement, the most important and
challenging issue, was the improvement of catalyst durability.
Furthermore, the improvement of A/F control considering NOx
adsorption performance and NH₃-SCR performance was carried out.
As a result, a new LNC system which has high performance even in
low exhaust gas temperature was established by new technologies
applied to the LNC and improved A/F control.