Fabrizio Forloni

Illegal manipulation (i.e., tampering) of vehicles is a severe problem because vehicle emissions increase orders of magnitude and significantly impact the environment and human health. This study measured the emissions before and after representative approaches of tampering of two Euro 6 Diesel light-duty passenger cars, two Euro VI Diesel heavy-duty trucks, and a Stage IV Diesel non-road mobile machinery (NRMM) agricultural tractor. With tampering of the selective catalytic reduction (SCR) for NO_x, the NO_x emissions increased by more than one order of magnitude exceeding 1000 mg/km (or mg/kWh) for all vehicles, reaching older Euro or even pre-Euro levels. The tampering of the NO_x sensor resulted in relatively low NO_x increases, but significant ammonia (NH₃) slip. The particle number emissions increased three to four orders of magnitude, reaching 6–10 × 10¹² #/km for the passenger car (one order of magnitude higher than the current regulation limit). The tampered passenger car’s NO_x and particle number emissions were one order of magnitude higher even compared to the emissions during a regeneration event. This study confirmed that (i) tampering with the help of an expert technician is still possible, even for vehicles complying with the current Euro standards, although this is not allowed by the regulation; (ii) tampering results in extreme increases in emissions.

The emissions of vehicles are measured in laboratories with roller-type chassis dynamometers, which simulate road driving resistances. Hub-coupled dynamometers, which are not included in the regulations for emission measurements, are commonly used for research and development purposes, for example, to assess powertrain capabilities, simulate on-road trips, and calibrate the control of individual wheels. As they do not need particular infrastructure and offer a wider range of applications, they could be a more economical alternative, especially if they could also be used for emission measurements for the type approval of vehicles. Nevertheless, the two types have not been directly compared in the literature, and, thus, their equivalency, especially regarding emission measurements, is not known. In this study, the emissions of a diesel and a gasoline plug-in vehicle were compared using the same analytical equipment and by switching only the roller and hub dynamometers. The diesel vehicle was further tested on a second roller-type dynamometer with the same driver and a second driver. The results of the two dynamometer types were very close, even though the repeatability of the measurements was very narrow. The main message of this work is that hub-type dynamometers can be used interchangeably with roller-type dynamometers. The points that need to be addressed, such as the determination of dynamic wheel radius and tire slip level, are also discussed.

The European Union (EU) has introduced since the early 1990s a series of progressively more stringent emission regulations to control air pollution from the transport sector, commonly known as Euro standards. Following this path, more recently, with the European Green Deal, the European Commission has indicated the intention to review the current air pollutant emissions standards. This study investigates the emission performance of an advanced demonstrator vehicle developed to meet the increasingly more stringent air pollution limits required. Emissions of currently regulated and unregulated components including NH₃, N₂O, and SPN₁₀ (solid particle number), were studied in a very wide range of real-world operative conditions. The performance of two new generation portable instruments for the onboard measurement of N₂O and NH₃ were also evaluated in comparison with reference laboratory equipment. Similarly, the measurement accuracy of onboard NOx sensors was also compared to laboratory reference. The vehicle presented low emissions of NOx and NH₃ and relatively low emissions of N₂O, also compared to data currently available in the literature, in a broad range of operative conditions, which however resulted in a large variability in emissions.

The Euro 4 regulation, applicable since 2016 for L-category vehicles (i.e., two and three-wheelers, and mini cars) reduced the emission limits, but also introduced a new cycle, the WMTC (World Harmonized Motorcycle Test Cycle). The emission studies of Euro 4 motorcycles are limited, and most importantly there are no published studies comparing the results of different laboratories applying the new cycle. In this study we compared the particle and gaseous pollutants of one Euro 4 motorcycle measured in two laboratories in 2017 and 2020. The gaseous pollutant results had a variance (one standard deviation of the means) of 0.5% for CO₂, 4–19% for CO, NO_x, HC (hydrocarbons) and SPN (Solid Particle Number). The particulate matter mass results had higher variance of 50–60%. Additional tests with open configuration to mimic dilution at the tailpipe gave equivalent results to the closed configuration for the gaseous pollutants and SPN. The total particles (including volatiles) had significant differences between the two configurations, with the closed configuration giving higher results. The main conclusion of this study is that the new procedures have very good reproducibility, even for the SPN that is not regulated for L-category vehicles. However, the measurement of total particles needs attention due to the high sensitivity of volatile particles to the sampling conditions.

The development and utilization of a series of after-treatment devices in modern vehicles has led to an increase in emissions of NH₃ and/or N₂O with respect to the past. N₂O is a long-lived greenhouse gas and an ozone-depleting substance, while NH₃ is a precursor of secondary aerosols in the atmosphere. Certain regions, e.g., the EU and the USA, have introduced limits to the emissions of NH₃ or N₂O for vehicles tested in the laboratory. However, due to the lack of on-board systems that allow for the measurement of these compounds when the regulations were developed, these vehicles’ real-world emissions have not been regulated. This work evaluates on-board systems that could allow measuring real-world emissions of NH₃ and N₂O from heavy-duty vehicles. In particular, emissions of NH₃ or N₂O from a Euro VI Step D urban/interurban bus fueled with Compressed Natural Gas were measured using the HORIBA’s OBS-ONE-XL, which is based on a specifically developed technique called Infrared Laser Absorption Modulation, and uses a Quantum Cascade Laser as a light source. They were also measured using the PEMS-LAB, which is a more conventional FTIR-based system. Emissions were measured under real-world driving conditions on the road and in a climatic test cell at different ambient temperatures. For most of the conditions tested, the on-board systems correlated well with a laboratory-grade FTIR used as reference. In addition, a good correlation with R² > 0.9 was found for the N₂O concentrations measured by OBS-ONE-XL and PEMS-LAB during on-road testing.

In the last years, the in-use emissions of vehicles are measured on the road with portable emissions measurement systems (PEMS). PEMS cannot measure as accurately as the laboratory grade equipment, and studies on their measurement uncertainty have continued since their appearance in the market. In this study we compared PEMS to laboratory grade equipment in Italian laboratories testing a diesel “Golden” (i.e., reference) vehicle for two consecutive years. The results showed equal means of PEMS and laboratory grade equipment for carbon dioxide (CO₂), nitrogen oxides (NO_x), and particle number (PN), with a variability of ±5 g/km for CO₂, ±10 mg/km for NO_x, and ±1 × 10¹¹ p/km for PN, which further decreased in the second year. For carbon monoxide (CO), the PEMS were on average 5–20 mg/km higher than the bags (variability ±40 mg/km). The main conclusion of this study is that PEMS are accurate under controlled laboratory ambient conditions, without any indications of significant bias.

The recent Euro 4 and 5 environmental steps for L-category vehicles (e.g., mopeds, motorcycles) were mainly designed to reduce the emissions of particulate matter and ozone precursors, such as nitrogen oxides and hydrocarbons. However, the corresponding engine, combustion, and aftertreatment improvements will not necessarily reduce the solid particle number (SPN) emissions, suggesting that a SPN regulation may be necessary in the future. At the same time, there are concerns whether the current SPN regulations of passenger cars can be transferred to L-category vehicles. In this study we quantified the errors and uncertainties in emission measurements, focusing on SPN. We summarized the sources of uncertainty related to emission measurements and experimentally quantified the contribution of each uncertainty component to the final results. For this reason, gas analyzers and SPN instruments with lower cut-off sizes of 4 nm, 10 nm, and 23 nm were sampling both from the tailpipe, and from the dilution tunnel having the transfer tube in closed or open configuration (i.e., open at the tailpipe side). The results showed that extracting from the tailpipe 23–28% of the mean total exhaust flow (bleed off) resulted in a 24–31% (for CO₂) and 19–73% (for SPN) underestimation of the emissions measured at the dilution tunnel. Erroneous determination of the exhaust flow rate, especially at cold start, resulted in 2% (for CO₂) and 69–149% (for SPN) underestimation of the tailpipe emissions. Additionally, for SPN, particle losses in the transfer tube with the closed configuration decreased the SPN concentrations around 30%, mainly due to agglomeration at cold start. The main conclusion of this study is that the open configuration (or mixing tee) without any instruments measuring from the tailpipe is associated with better accuracy for mopeds, especially related to SPN measurements. In addition, we demonstrated that for this moped the particle emissions below 23 nm, the lower size currently prescribed in the passenger cars regulation, were as high as those above 23 nm; thus, a lower cut-off size is more appropriate.

Modern (Euro VI) heavy-duty vehicles have significantly lower pollutant emissions than older vehicles. However, there are still concerns regarding the emissions of refuse collection vehicles in cities, because in some cases they may use engines designed for long haulage trucks. For this reason, we tested a diesel Euro VI (step C) refuse collection heavy-duty vehicle, both in the laboratory on a chassis dynamometer and on the road, similar to the regulated in-service conformity cycle, but also with actual refuse collection cycles. Particle number (PN) and gaseous pollutants (NO_x, CO, HC) were measured using a Portable Emissions Measurement System (PEMS). Additionally, in the laboratory we used laboratory grade gaseous, particle number, and FTIR (Fourier-transform infrared spectroscopy) systems to assess the PEMS. For short periods, where the exhaust gas temperature was low for the aftertreatment devices (cold start, some city conditions), the NO_x emissions reached 2000 mg/km. Nevertheless, all pollutants were well below the applicable emissions limits expressed in mg/kWh for all cycles examined (in brackets the ratio to the laboratory limit): NO_x < 400 mg/kWh (0.87), CO < 850 mg/kWh (0.21), HC < 12 mg/kWh (0.08), PN < 2.4×10¹⁰ p/kWh (0.04). To make sure that this will always be the case, future heavy-duty type approval emissions regulations should specifically consider the urban conditions for municipality vehicles, such as refuse trucks.