Ammonia on a LNT: Avoid the Formation or Take Advantage of It

As the reduction of particulates already has made its way into diesel passenger cars in form of the DPF, the reduction of NOx will be the next necessary step to comply with future emission regulations. Lean NOx traps have proven to be a promising technology to achieve these targets. A lot of research already has been done on the principal mechanisms of the loading and regeneration cycles as well as system optimization. Less attention however was paid to the formation of secondary emissions during the regeneration process, especially ammonia.

In this study we investigated the influence of different parameters on the formation of ammonia during LNT regeneration. Extensive tests were carried out on an engine test bed equipped with a 6 cylinder Diesel engine, varying the amount of NOx stored, regeneration conditions (λ), regeneration duration and the parameters of the in-house developed port injection device. Based on these results a regeneration strategy was developed to minimize ammonia formation while at the same time obtaining a high NOx reduction efficiency. Finally as part of a complementary strategy the ammonia formed on the LNT was used as a reducing agent for a passive SCR system in order to further decrease the NOx emissions.