Regulated and Non-Regulated Emissions from Euro 6 Diesel, Gasoline and CNG Vehicles under Real-World Driving Conditions

Abstract

The transport sector is one of the main sources air pollutants. Different exhaust after-treatment systems have been implemented over the years to control the emissions of criteria pollutants. However, while reducing the emissions of the target compounds these systems can lead to the emissions of other pollutants and/or greenhouse gases such as NH 3 or N 2 O. Following the implementation of the Real Driving Emissions (RDE) test procedure in the EU, vehicles have been equipped with more complex after-treatment configurations. The impact that these technologies may have on the emissions of non-regulated pollutants during real-world driving have not been evaluated until now. In the current study we present the on-road emissions of a series of non-regulated pollutants, including NH 3 , N 2 O, CH 4 and HCHO, measured with a portable FTIR from a series of Euro 6d, Euro 6c and Euro 6d-TEMP, gasoline diesel and compressed natural gas (CNG) vehicles during real-world testing. The obtained results show that it is possible to measure N 2 O, NH 3 , CH 4 and HCHO during on-road operation. The results also highlight the importance of the measurement of the emissions of these pollutants during real-world driving, as the emissions of NH 3 (a particulate matter precursor) and those of N 2 O and CH 4 (green-house gases) can be high from some vehicle technologies. NH 3 emissions were up to 49 mg/km for gasoline passenger cars, up to 69 mg/km for the CNG light-commercial vehicle and up to 17 mg/km a diesel passenger car equipped with a selective catalytic reduction system (SCR). On the other hand, N 2 O and CH 4 emissions accounted for up to 9.8 g CO 2 eqv/km for a diesel passenger car equipped with a combination of diesel oxidation catalysts (DOC), lean NO x traps (LNT), SCR and possibly an ammonia slip catalyst ASC.Atmosphere 2020, 11, 204 2 of 18 organic compounds (NMVOCs) and CH 4 are the main precursors of ground-level (tropospheric) O 3 . Aiming at improving Europe's air quality, policy actions have increasingly been taken to address transport-related air pollution. At European Union (EU) level, this has included the regulation of emissions by setting emission standards (Euro 1 to Euro 6) or by setting requirements for fuel quality.To meet these standards, passenger cars have been equipped with different emission control systems. Thus, three-way catalytic converters (TWC) are commonly used to reduce the emissions of CO, hydrocarbons (HC) and NO x from gasoline cars. In the case of diesel cars, CO and HC emissions are reduced using diesel oxidation catalysts (DOC), and NO x emissions using selective catalytic reduction systems (SCR), lean NO x traps (LNT) or a combination of both. While reducing the emissions of the target compounds these systems can lead to the emissions of other pollutants that are not currently regulated for the passenger cars in the EU. The emitted pollutants include NH 3 [2,3] and N 2 O. In fact, several laboratory-based studies have indicated that vehicle emissions of NH 3 and N 2 O are linked to the use o...

Assessment of Gaseous and Particulate Emissions of a Euro 6d-Temp Diesel Vehicle Driven >1300 km Including Six Diesel Particulate Filter Regenerations

“…In this study, we measured the emissions of regulated and non-regulated pollutants of a diesel fueled vehicle both in the laboratory and on the road. For all regulated testing conditions, all currently regulated pollutants were below the applicable limits, in agreement with other studies of Euro 6d-temp diesel vehicles [45,46]. Particularly for NO x , which was the main attention topic for diesel vehicles until very recently, the emissions were below the applicable (and future) limits on the road even when DPF regeneration events occurred, and much lower compared to the pre-RDE Euro 6 diesel vehicles that were typically emitting on the road >4 times the limit [23,29,[54][55][56][57].…”

“…Only dynamic driving brought the NO x levels (200 mg/km) slightly higher than the limit (168 mg/km, using the applicable 2.1 conformity factor). Others have also reported that dynamic driving significantly increases the emissions [36,46]. The NO/NO x ratio was on average 78% in the laboratory tests and 65% in the on-road tests.…”

“…Regarding non-regulated pollutants, distance-specific NH 3 on the WLTP 23 • C test were lower than emissions on Euro 6 diesel vehicles equipped with SCR (7-8 mg/km) [46,[63][64][65], but similar (<1 mg/km) to Euro 6 diesel vehicles retrofitted with an ammonia slip catalyst in the underfloor position [33,46]. Isocyanic acid (HNCO) emissions (0.3 mg/km) were similar to those reported for Euro 6 SCR-equipped diesel vehicles (<1 mg/km) [46,64], but higher at 0 • C (3.5 mg/km). N 2 O (11-13 mg/km) and CH 4 (5-6 mg/km) on the WLTP 23 • C test were in the range of emissions from diesel vehicles reported by others [46,66].…”

“…Despite representing a small proportion of the circulating fleet, vehicles type-approved after the entry into force of the RDE and WLTP regulations shall become widespread with the turnover of the fleet, and it is therefore critical to assess their emissions performance to properly understand their contribution to air pollution. According to our knowledge, studies on diesel Euro 6-temp vehicles with state-of-the art aftertreatment architecture are limited [45,46]. This paper is organized as follows: Section 2 describes the characteristics of the vehicle, the instrumentation used, and provides details on the laboratory and on-road tests performed.…”

Exhaust emission factors of greenhouse gases (GHGs) from European road vehicles

“…It was found that vehicles fueled with diesel emitted significantly more N 2 O than the vehicles fueled with gasoline, E85 and the hybrid vehicles (p value of 4•10 −10 , 0.0008 and 0.0002, respectively). These findings are consistent with the results obtained over on-road tests where N 2 O emissions from two LDV gasoline were found non-detectable while two LDV diesel where emitting up to 27 mg/km [54]. High N 2 O emissions from diesel fueled LDV (ca.…”