Tailpipe emissions of a pool of 13 Euro 6b light-duty vehicles (eight diesel and five gasoline-powered) were measured over an extensive experimental campaign that included laboratory (chassis dynamometer), and on-road tests (using a portable emissions measurement system). The New European Driving Cycle (NEDC) and the Worldwide harmonised Light-duty vehicles Test Cycle (WLTC) were driven in the laboratory following standard and extended testing procedures (such as low temperatures, use of auxiliaries, modified speed trace). On-road tests were conducted in real traffic conditions, within and outside the boundary conditions of the regulated European Real-Driving Emissions (RDE) test. Nitrogen oxides (NO_X), particle number (PN), carbon monoxide (CO), total hydrocarbons (HC), and carbon dioxide (CO₂) emission factors were developed considering the whole cycles, their sub-cycles, and the first 300 s of each test to assess the cold start effect. Despite complying with the NEDC type approval NO_X limit, diesel vehicles emitted, on average, over the WLTC and the RDE 2.1 and 6.7 times more than the standard limit, respectively. Diesel vehicles equipped with only a Lean NO_X trap (LNT) averaged six and two times more emissions over the WLTC and the RDE, respectively, than diesel vehicles equipped with a selective catalytic reduction (SCR) catalyst. Gasoline vehicles with direct injection (GDI) emitted eight times more NO_X than those with port fuel injection (PFI) on RDE tests. Large NO_X emissions on the urban section were also recorded for GDIs (122 mg/km). Diesel particle filters were mounted on all diesel vehicles, resulting in low particle number emission (~10¹⁰ #/km) over all testing conditions including low temperature and high dynamicity. GDIs (~10¹² #/km) and PFIs (~10¹¹ #/km) had PN emissions that were, on average, two and one order of magnitude higher than for diesel vehicles, respectively, with significant contribution from the cold start. PFIs yielded high CO emission factors under high load operation reaching on average 2.2 g/km and 3.8 g/km on WLTC extra-high and RDE motorway, respectively. The average on-road CO₂ emissions were ~33% and 41% higher than the declared CO₂ emissions at type-approval for diesel and gasoline vehicles, respectively. The use of auxiliaries (AC and lights on) over the NEDC led to an increase of ~20% of CO₂ emissions for both diesel and gasoline vehicles. Results for NO_X, CO and CO₂ were used to derive average on-road emission factors that are in good agreement with the emission factors proposed by the EMEP/EEA guidebook.

Background: Divergence in fuel consumption (FC) between the type-approval tests and real-world driving trips, known also as the FC gap, is a well-known issue and Europe is preparing the field for tackling it. The present study focuses on the monitoring of the FC of a single vehicle throughout 1 year with 20 different drivers and almost 14,000 km driven with the aim to analyze and quantify the true intrinsic variability in the FC gap coming from environmental and traffic conditions and driving factors. In addition, the regression model has been developed to evaluate the importance of these different factors on the FC gap’s variability. Results: The 1-year FC gap measured in this study was 29% while driver’s averages were in the range from 16 to 106%. The regression model developed had $$R^{2}$$R2 equal to 90.4 meaning that more than 90% of the FC gap’s variance can be explained with this model and factors measured in this study. The results of the model showed that among all factors analyzed the highest contribution in the FC gap’s variance is coming from the average vehicle speed (16.6%), followed by the road grade (13.4%), and trip distance (10.1%). Indeed, the highest FC gaps are measured when the average vehicle speeds were below 20 km/h, the average distance-weighted road grades above 1%, and the trip distances below 5 km. In addition, the impact of driver factors is not negligible (25%) and the highest FC gap is measured for the trips where average positive acceleration was higher than 0.7 m/s² (indicating aggressive driving) and the electric power demand higher than 800 W. Conclusions: The future lifetime on-board fuel consumption reporting is a crucial instrument that will allow the monitoring of the evolution of the FC gap and ensuring that it does not increase over time. The analysis presented in this study is a basis for setting up a more detailed and refined prediction model, which could assist the European Commission in closely monitoring the gap and the underlying factors generating it.

A new vehicle testing procedure (WLTP - Worldwide Light duty vehicle Test Procedure) was introduced in the European Union (EU) in 2017. In order to examine its actual impact on CO₂ emissions for different vehicle technologies and categories, this study analysed data from vehicles certified and registered in the EU in 2019 and 2020. It was found that in average, for all vehicles sold in 2020, the increase in CO₂ emissions due to the intoduction of the WLTP was 21% for passenger cars and 27% for vans. Also that diesel vehicles are impacted more than gasoline ones and that the impact on conventional hybrid vehicles is 27% and plug-in hybrid vehicles between 0% (in 2020) and 11% (in 2019). Models employed revealed that the increase in CO₂ is mainly due to the higher test masses and more realistic road load coefficients of WLTP that result in higher cycle energy demands. Moreover, results confirmed that the impact of the WLTP's introduction is in line, both in terms of absolute increase and variability, with model-based predictions performed before fleet-wide data were made available.

The introduction of a solid particle number limit for vehicles with gasoline direct injection (GDI) engines resulted in a lot of research and improvements in this field in the last decade. The requirement to also fulfil the limit in the recently introduced real-driving emissions (RDE) regulation led to the introduction of gasoline particulate filters (GPFs) in European vehicle models. As the pre-standardisation research was based on engines, retrofitted vehicles and prototype vehicles, there is a need to better characterise the actual emissions of GPF-equipped GDI vehicles. In the present study we investigate one of the first mass production vehicles with GPF available in the European market. Regulated and non-regulated pollutants were measured over different test cycles and ambient temperatures (23 °C and −7 °C) in the laboratory and different on-road routes driven normally or dynamically and up to 1100 m altitude. The results showed that the vehicle respected all applicable limits. However, under certain conditions high emissions of some pollutants were measured (total hydrocarbons emissions at −7 °C, high CO during dynamic RDE tests and high NO_x emissions in one dynamic RDE test). The particle number emissions, even including those below 23 nm, were lower than 6 × 10¹⁰ particles/km under all laboratory test cycles and on-road routes, which are <10% of the current laboratory limit (6 × 10¹¹ particles/km).