NOx emissions from diesel light duty vehicle tested under NEDC and real-word driving conditions

The interest of NOx engine emissions from diesel engines has been increasing during the last years. Particularly, the comparison of the real driving NOx emissions with the results obtained during homologation procedures has received a great attention. The main goal of this paper is to provide a statistical methodology, able to compare two different types of driving pattern conditions and the corresponding NOx engine emissions. In the present work, the two types of driving pattern analysed are the real-world driving and the chassis dyno following the New European Driving Cycle (NEDC). For the sake of generality, two types of circuits (Urban and Extra-urban) have been selected. A light-duty diesel vehicle, equipped with the same after-treatment system as Euro 5 engines, was used as a test vehicle. Although in this certifications only new vehicles have to fulfil Euro 6d temp, Real Driving Emissions test (RDE) is mandatory, it is necessary to quantify the real-world driving emissions for the previous certifications (Euro 5 and Euro 4 vehicles). The statistical study demonstrates the existence of significant differences among the fundamental variables of the engine (desired injection quantity, engine speed, vehicle velocity, exhaust gas recirculation (EGR) valve opening and NOx measured emissions) when real driving and NEDC procedures are compared. Although these results have been obtained by a deductive way, they led us to state that real driving NOx emissions strongly differs from NEDC driving ones. Therefore, this manuscript constitutes a further more proof of the non-representativeness of NEDC procedure as vehicle certification procedure.