Modelling of a combined image storage and image-SCR catalytic system for Diesel exhaust gas aftertreatment

A combined Diesel exhaust gas aftertreatment system is studied, consisting of the image storage and reduction catalyst (NSRC, called also lean image trap, LNT) and the catalyst for selective catalytic reduction of image by image (image-SCR). Most of the time the system is operated under prevailing fuel-lean conditions, enabling economical running of the engine. During this phase the image emissions are being adsorbed in the NSRC. However, short fuel enrichments need to be applied periodically for the NSRC regeneration (reduction of the stored image). Ammonia produced in the NSRC as a by-product of the image reduction under controlled fuel-rich conditions is then adsorbed in the image-SCR reactor located downstream. The adsorbed image is consequently utilised in selective image reduction during the next fuel-lean period. The image configuration thus eliminates the need for an external image source (e.g., periodically re-filled urea solution tank) that is necessary in the case of the stand-alone SCR.