RESEARCH ARTICLE Assessment of Euro 5 diesel vehicle NOx emissions by laboratory and track testing Maria Vittoria Prati 1 & Maria Antonietta Costagliola 1 & Andrea Zuccheroso 1 & Pierpaolo Napolitano 1 Received: 9 July 2018 /Accepted: 5 February 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract The Volkswagen scandal has promoted experimental campaigns worldwide aimed to assess the real exhaust emissions of in-use vehicles. Attention has been paid to diesel vehicle NOx emissions that are much higher than legislative type-approval limits. This paper analysed exhaust emissions of a fleet of ten Euro 5 diesel vehicles. NOx emissions were measured during laboratory and track testing. In both cases, the type-approval test was carried out with cold and warm starts. Moreover, in the laboratory, a modified type-approval test and a real urban driving cycle were executed in order to characterise emissions in multiple operating conditions, outside of the homologation boundaries. The testing environment did not influence the emissions behaviour of the tested vehicles. Track and laboratory results, in fact, were comparable when ambient conditions were comparable. The parameter which played the main role in terms of NOx emissions is the ambient temperature, fixed at 23 °C in laboratory and not controlled on the track. Above 28 °C, NOx emissions were much higher than the approval limit (almost 600 mg/km). Moreover, warm driving cycles always introduced higher NOx emissions than cold ones, because of the partial use and/or deactivation of the EGR circuit (one of effective measures to reduce NOx formation). The ratio between warm and cold emissions ranged from 2 to 5. The engine parameter which helped explain the relationship between NOx emissions and thermal engine status was the intake air temperature. For intake air temperatures below 40 °C, NOx emissions were lower than 0.2 g/km. Above 40 °C, they suddenly increased up to almost 0.6 g/km. Another issue highlighted by the experimental results was that dynamic real driving caused the highest NOx emissions (almost 1 g/km). Keywords Exhaust emissions . NOx . EGR . Intake air temperature . Track test . Diesel cars Introduction In 2015, following a notice of violation by the US-EPA, Volkswagen Group admitted the use of a defeat device that was installed in almost 11 million diesel engines to circumvent emission tests. The illegal software was able to activate the normal use of NOx after-treatment devices during type- approval testing. Outside homologation conditions, NOx abatement systems were deactivated, generating NOx emis- sions approximately 21 times the amount legally permitted in the USA (0.9 g/km against 0,043 g/km) (Thompson et al. 2014). Following this scandal, many European countries started an investigation into whether other manufacturers were using equivalent prohibited devices and to better understand why emission results in the real world were significantly different from those tested under laboratory conditions (UK 2016; Republique Francaise 2016; The Netherlands 2016). The VW affair has spotlighted an issue well known in the scientific community for years. Several papers have dealt with diesel NOx emissions that repeatedly exceeded the Euro 5 limit outside of type-approval conditions (Fontaras et al. 2014; Degraeuwe and Weiss 2017; Ntziachristos et al. 2016; Responsible editor: Philippe Garrigues * Maria Antonietta Costagliola m.a.costagliola@im.cnr.it Maria Vittoria Prati m.v.prati@im.cnr.it Andrea Zuccheroso andreazuccheroso@gmail.com Pierpaolo Napolitano p.napolitano@im.cnr.it 1 Istituto Motori – National Research Council of Italy, Viale Marconi, 4, 80125 Naples, Italy Environmental Science and Pollution Research https://doi.org/10.1007/s11356-019-04486-7