Evaluation of exhaust gas recirculation as a technique for reducing dieselengine NOx emissions

The aim of this work is to evaluate the potential of exhaust gas recirculat ion (EGR) to reduce NOx emissions, through the most significant parameters, and to delimit the application range of this technique. Therefore, a detai led analysis of experimental results on NOx formation and emissions is pres ented, and the mechanisms by which EGR affects them are explained. A collec tion of five different automotive diesel engines, all of them from Nissan, was tested, so it was possible to distinguish the combined effect of EGR an d their main characteristics, such as supercharging, intercooling, size, co mpression ratio and combustion chamber type [direct injection (DI) and indi rect injection (IDI)]. The engines were tested in a set of steady condition s, trying to reproduce the different operating modes of the European transi ent urban/extra-urban certification cycle. In this way, comparisons between different engine emissions provided conclusions directly related to the em ission certification limits.