Variability in operation-based NOx emission factors with different test routes, and its effects on the real-driving emissions of light diesel vehicles Original Research Article

The objective of this study is to quantify the differences in NOx emissions between standard and non-standard driving and vehicle operating conditions, and to estimate by how much NOx emissions exceed the legislative emission limits under typical Korean road traffic conditions. Twelve Euro 3–5 light-duty diesel vehicles (LDDVs) manufactured in Korea were driven on a chassis dynamometer over the standard New European Driving Cycle (NEDC) and a representative Korean on-road driving cycle (KDC). NOx emissions, average speeds and accelerations were calculated for each 1-km trip segment, so called averaging windows. The results suggest that the NOx emissions of the tested vehicles are more susceptible to variations in the driving cycles than to those in the operating conditions. Even under comparable operating conditions, the NOx control capabilities of vehicles differ from each other, i.e., NOx control is weaker for the KDC than for the NEDC. The NOx emissions over the KDC for given vehicle operating conditions exceed those over the NEDC by more than a factor of 8. Consequently, on-road NOx emission factors are estimated here to exceed the Euro 5 emission limit by up to a factor of 8, 4 and 3 for typical Korean urban, rural, and motorway road traffic conditions, respectively. Our findings support the development of technical regulations for supplementary real-world emission tests for emission certification and the corresponding research actions taken by automotive industries.