Experimental Study of Lean NOx Trap Management

Lean NOx Trap (LNT) catalysts are capable of reducing exhaust NOx emissions from Diesel engines. NOx is stored on the catalyst substrate during the normal engine operation (lean mixture) and is reduced under rich exhaust condition (rich mixture) during the regeneration event. There are different methods to obtain the rich conditions and one of this is the so called “in cylinder” regeneration. This technique is feasible if the engine is equipped with electronic injection system (i.e. Common Rail system), in fact it is possible to obtain rich Air/Fuel ratios conditions using different injection strategies. Generally, one method to obtain the rich condition for the LNT regeneration consists of additional fuel's injection into the engine cylinders while acting at the same time on EGR and Throttle Valve to reduce the intake air flow.In this study a 1.9 liter CR Diesel engine with a LNT catalyst system was used to evaluate different regeneration techniques and to characterize the catalyst substrate performance. The aim of this work was the evaluation of different engine parameters' influence on A/F ratio to obtain the rich condition by the realization of an experimental Design of Experiment (DOE) plane. Several experimental tests were carried out to evaluate the effects of different injection strategies (Pilot +delayed Main injection, Main +Post injection, etc) on A/F ratio, while keeping under control HC and CO emissions.