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

The aim of this work is to evaluate the potential of exhaust gas recirculation (EGR) to reduce NOx emissions, through the most significant parameters, and to delimit the application range of this technique. Therefore, a detailed analysis of experimental results on NOx formation and emissions is presented, and the mechanisms by which EGR affects them are explained. A collection of five different automotive diesel engines, all of them from Nissan, was tested, so it was possible to distinguish the combined effect of EGR and their main characteristics, such as supercharging, intercooling, size, compression ratio and combustion chamber type [direct injection (DI) and indirect injection (IDI)]. The engines were tested in a set of steady conditions, trying to reproduce the different operating modes of the European transient urban/extra-urban certification cycle. In this way, comparisons between different engine emissions provided conclusions directly related to the emission certification limits.