Solid Particle Number Emission Factors of Euro VI Heavy-Duty Vehicles on the Road and in the Laboratory

Regulated and unregulated emissions from Euro VI Diesel and CNG heavy-duty vehicles

This study compares emissions from Euro VI-D Diesel and CNG buses across temperatures from -7 °C to 35 °C. Pollutants including NOx, THC, CH4, CO, NH3, N2O, HCHO, Solid Particle Number larger than 23 nm (SPN23) and larger than 10 nm (SPN10) were measured. Both buses complied with Euro VI-D but exceeded European Commission's proposed Euro 7 limits, notably for NOx and SPN10. The CNG bus also surpassed NH3, CO, and CH4 limits, while the Diesel exceeded N2O limits. High NH3 emissions were observed from CNG (up to 0.320 g/kWh), with Diesel reporting lower levels (up to 0.021 g/kWh). HCHO emission from both vehicles were very low. SPN23 was under limits, but SPN10 exceeded Euro 7 limits at cold start tests. CNG's CH4 and N2O emissions constituted up to 4.6% and 3.5% of CO2 equivalent, respectively. Diesel bus showed negligible CH4 but N2O emissions represented up to 37% of CO2 equivalent.

Towards zero pollution vehicles by advanced fuels and exhaust aftertreatment technologies

Vehicular emissions deteriorate air quality in urban areas notably. The aim of this study was to conduct an in-depth characterization of gaseous and particle emissions, and their potential to form secondary aerosol emissions, of the cars meeting the most recent emission Euro 6d standards, and to investigate the impact of fuel as well as engine and aftertreatment technologies on pollutants at warm and cold ambient temperatures. Studied vehicles were a diesel car with a diesel particulate filter (DPF), two gasoline cars (with and without a gasoline particulate filter (GPF)), and a car using compressed natural gas (CNG). The impact of fuel aromatic content was examined for the diesel car and the gasoline car without the GPF. The results showed that the utilization of exhaust particulate filter was important both in diesel and gasoline cars. The gasoline car without the GPF emitted relatively high concentrations of particles compared to the other technologies but the implementation of the GPF decreased particle emissions, and the potential to form secondary aerosols in atmospheric processes. The diesel car equipped with the DPF emitted low particle number concentrations except during the DPF regeneration events. Aromatic-free gasoline and diesel fuel efficiently reduced exhaust particles. Since the renewal of vehicle fleet is a relatively slow process, changing the fuel composition can be seen as a faster way to affect traffic emissions.

Quantification of green infrastructure effects on airborne nanoparticles dispersion at an urban scale

Many dispersion models are available to simulate the mass concentrations of particulate matter in an urban environment. Still, fewer are capable of simulating the effect of green infrastructure (GI) on the airborne nanoparticles represented by total particle number concentration (ToNC). We developed an integrated approach capable of simulating the dispersion of airborne nanoparticles under the various scenarios of green infrastructure. We demonstrated the usefulness of this approach by simulating a high-resolution spatial (250 × 250 m) concentration of traffic-emitted airborne nanoparticles at an urban scale under eight GI urban planning scenarios: the base year 2015 (2015-Rl-GI); business-as-usual for 2039 (2039-BAU-GI); three hypothetical future scenarios with maximum possible coniferous (2039-HMax-Con), deciduous (2039-HMax-Dec) trees, and grassland (2039-HMax-Grl) over the available land; and three alternative future scenarios by considering coniferous (2039-HNR-Con), deciduous (2039-HNR-Dec) trees, and grassland (2039-HNR-Grl) around traffic lanes. We assessed both the parametric and structural uncertainties due to particle transformation processes (nucleation, coagulation and deposition) and uncertainty in particle number emission factors (PNEFs) on ToNC, respectively. We also simulated the combined impact of deposition and aerodynamic dispersion of GI on ToNC reduction. The annual average ToN emission (ToNE) reduced from 5.36 × 10²² (2015) to 2.84 × 10²¹ (2039) particles due to the UK's air quality plan in future. Parametric uncertainty due to variable PNEFs might cause variation in annual ToNC from -57% to +60%. However, structural uncertainties in ToNC, due to particle transformation processes were up to -12%, -11% and +0.14% for deposition, coagulation, and nucleation, respectively. The annual ToN deposition (ToND) and concentration were 28-4800 × 10¹⁹ particles and 3.94-19.10 × 10³ # cm^-3, respectively, depending on the percentage share of GI type and annual traffic emissions. Planting maximum coniferous trees (2039-HMax-Con) simulated maximum reduction in annual ToNC. Coniferous trees near traffic lanes (2039-HNR-Con) also found to be more effective to reduce annual ToNC.

Emissions of Euro 6 Mono- and Bi-Fuel Gas Vehicles

Compressed natural gas (CNG) and liquefied petroleum gas (LPG) are included in the group of promoted transport fuel alternatives in Europe. Most studies on emissions factors are based on old technology CNG and LPG fueled vehicles. Furthermore, there are not many data at low ambient temperatures, on-road driving, or unregulated pollutants, such as ammonia (NH3). In this study we measured the emissions of one Euro 6b CNG light commercial vehicle, one Euro 6b and one Euro 6d-Temp bi-fuel LPG passenger car, one Euro 6d-Temp bi-fuel CNG passenger car, and four Euro 6d-Temp CNG passenger cars. Tests included on-road testing and worldwide harmonized light vehicles test cycles (WLTC) in the laboratory with cold and hot engine, at 23 °C and −7 °C. The results showed 10–23% CO2 savings in gas modality compared to gasoline, lower CO and particle number emissions, and relatively similar total and non-methane hydrocarbons and NOx emissions. The ammonia emissions were high for all vehicles and fuels; higher than gasoline and diesel vehicles. The results also showed that, following the introduction of the real-driving emissions regulation, even though not applicable to the examined vehicles, Euro 6d-Temp vehicles had lower emissions compared to the Euro 6b vehicles.

Effect of Tampering on On-Road and Off-Road Diesel Vehicle Emissions

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 NOx, the NOx 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 NOx sensor resulted in relatively low NOx 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 NOx 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.

Elevated emissions of volatile and nonvolatile nanoparticles from heavy-duty diesel engine running on diesel-gas co-fuels

This study experimentally examines the effects of four diesel-gas co-fuels, two engine loads and an aftertreatment on regulated and unregulated emissions from a 6-cylinder natural-aspirated direct-injection heavy-duty diesel engine (HDDE) with an engine dynamometer. Fuel energy of ultra-low-sulfur diesel was substituted with 10% and 20% of gas fuels, including pure H₂, CH₄, and two CH₄-CO₂ blends. The particle number size distributions of volatile and nonvolatile nanoparticles were measured under ambient temperature and after 300 °C heating, respectively. The results show that the gas fuels caused increases of hydrocarbon emission, slight changes of NOx emission, and decreases of opacity. All four gas fuels resulted in elevated emissions of both volatile and nonvolatile nanoparticles at 25% and 75% load, in the range of 29% to 390%. The increased emissions of volatile nanoparticles were variable and without obvious trends. Special attentions should be given to the addition of H₂ under high load, during which significant increases of volatile nanoparticles could be formed not only post-combustion (up to 1376%), but also post-diesel oxidation catalyst plus diesel particulate filter (DOC + DPF). The nonvolatile nanoparticles, on the other hand, could be effectively removed by the retrofitted DOC + DPF, with efficiency >98.2%. A noteworthy fraction of solid particles of sizes <23 nm were found in the exhaust, not being accounted for by current regulatory emission standard.

Detailed Characterization of Solid and Volatile Particle Emissions of Two Euro 6 Diesel Vehicles

The solid particle number emissions of Diesel vehicles are very low due to the particulate filters as exhaust aftertreatment devices. However, periodically, the trapped particles are oxidized (i.e., active regeneration) in order to keep the backpressure at low levels. The solid particle number emissions during regenerations are only partly covered by the regulations. Many studies have examined the emissions during regenerations, but their contribution to the overall emissions has not been addressed adequately. Furthermore, the number concentration of volatile particles, which is not included in the regulations, can be many of orders of magnitude higher. In this study, the particulate emissions of two light-duty Euro 6 vehicles were measured simultaneously at the tailpipe and the dilution tunnel. The results showed that the weighted (i.e., considering the emissions during regeneration) solid particle number emissions remained well below the applicable limit of 6 × 1011 #/km (solid particles > 23 nm). This was true even when considering solid sub-23 nm particles. However, the weighted volatile particle number emissions were many orders of magnitude higher, reaching up to 3 × 1013 #/km. The results also confirmed the equivalency of the solid particle number results between tailpipe and dilution tunnel locations. This was not the case for the volatile particles which were strongly affected by desorption phenomena. The high number of volatiles during regenerations even interfered with the 10 nm solid particle number measurements at the dilution tunnel, even though a catalytic stripper equipped instrument was also used in the dilution tunnel.

Measuring Emissions from a Demonstrator Heavy-Duty Diesel Vehicle under Real-World Conditions—Moving Forward to Euro VII

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.

Transportation and Air Quality Perspectives and Projections in a Mediterranean Country, the Case of Greece

This study provides a thorough review and analysis of the evolution of the Greek vehicle fleet over the last ~30 years, which is next used for the generation of high granularity fleet projections, the assessment of associated air pollution and the estimation of relevant environmental benefits by 2030. The integrated methodology developed takes also into account vehicle clustering and the Brown’s Double Simple Exponential Smoothing technique that, together with the adoption of COPERT-based emission factors, allow for the estimation of the anticipated emissions in 2030. Expected 2030 emissions levels suggest a reduction across all pollutants compared to 2018, ranging from 3.7% for PM10 to 54.5% for NMVOC (and 46% for CO, 14% for SO2, 28% for NOX and 21% for CO2). We find that Greece is on track with national goals concerning the reduction of air pollution from the transportation sector, which designates the positive contribution anticipated by EVs and new, “greener” vehicles, and sets new challenges for the further improvement of the sector beyond the 2030 outlook.

Revisiting Total Particle Number Measurements for Vehicle Exhaust Regulations

Road transport significantly contributes to air pollution in cities. Emission regulations have led to significantly reduced emissions in modern vehicles. Particle emissions are controlled by a particulate matter (PM) mass and a solid particle number (SPN) limit. There are concerns that the SPN limit does not effectively control all relevant particulate species and there are instances of semi-volatile particle emissions that are order of magnitudes higher than the SPN emission levels. This overview discusses whether a new metric (total particles, i.e., solids and volatiles) should be introduced for the effective regulation of vehicle emissions. Initially, it summarizes recent findings on the contribution of road transport to particle number concentration levels in cities. Then, both solid and total particle emission levels from modern vehicles are presented and the adverse health effects of solid and volatile particles are briefly discussed. Finally, the open issues regarding an appropriate methodology (sampling and instrumentation) in order to achieve representative and reproducible results are summarized. The main finding of this overview is that, even though total particle sampling and quantification is feasible, details for its realization in a regulatory context are lacking. It is important to define the methodology details (sampling and dilution, measurement instrumentation, relevant sizes, etc.) and conduct inter-laboratory exercises to determine the reproducibility of a proposed method. It is also necessary to monitor the vehicle emissions according to the new method to understand current and possible future levels. With better understanding of the instances of formation of nucleation mode particles it will be possible to identify its culprits (e.g., fuel, lubricant, combustion, or aftertreatment operation). Then the appropriate solutions can be enforced and the right decisions can be taken on the need for new regulatory initiatives, for example the addition of total particles in the tailpipe, decrease of specific organic precursors, better control of inorganic precursors (e.g., NH3, SOx), or revision of fuel and lubricant specifications.

Experimental Investigation on the DPF High-Temperature Filtration Performance under Different Particle Loadings and Particle Deposition Distributions

Based on DPF filtration and regeneration bench, the solid particle emission and high-temperature filtration characteristics of different carbon black particle loadings and particle deposition distributions are studied. The aerosol generator (PAlAS RGB 1000) is used to introduce carbon black particles into the inlet of a DPF, and the NanoMet3 particle meter is used to measure the solid particle concentration at the inlet and outlet of a DPF to obtain the filtration characteristics. Previous studies found that without inlet carbon black particles, there was an obvious solid particle emission peak at the outlet of the deposited DPF during the heating, and the concentration increased by 1–2 orders of magnitude. In this paper, the high-temperature filtration characteristics under steady-state temperature conditions are studied. It is found that a DPF can reduce the range of inlet fluctuating particles, and with the increase of temperature, the proportion of large solid particles in the outlet particles increases, and the size distribution range decreases. Particle loading has positive and negative effects on the DPF filtration, and the DPF has the optimal particle loading, which makes the comprehensive filtration efficiency improve the highest. The deposition transition section can make the deposition particles in the DPF uniform, but the filtration efficiency is reduced.

Investigations of Exhaust Emissions from Rail Machinery during Track Maintenance Operations

The paper presents the investigations of exhaust emissions under actual operation of two rail vehicles: a track geometry vehicle and a clearance vehicle. The environmental assessment of this type of objects is difficult due to the necessity of adapting the measurement equipment and meeting the safety requirements during the tests (particularly regarding the distance from the overhead electrical lines). The authors have proposed and developed a unique research methodology, based on which a detailed exhaust emissions analysis (CO, HC, NOx, and PM) was carried out. The complex assessment included the unit and on-track exhaust emissions. In the analyses, the authors also included the operating conditions of the powertrains of the tested machinery. The obtained environmental indexes were referred to the homologation standards, according to which the vehicles were approved for operation. Due to the nature of operation of the tested vehicles, the authors carried out a comprehensive environmental assessment in the daily and annual approach as well as in the aspect of their operation as combined vehicles, which is a novel approach to the assessment of the environmental performance of this type of objects.

Non-Volatile Particle Number Emission Measurements with Catalytic Strippers: A Review

Vehicle regulations include limits for non-volatile particle number emissions with sizes larger than 23 nm. The measurements are conducted with systems that remove the volatile particles by means of dilution and heating. Recently, the option of measuring from 10 nm was included in the Global Technical Regulation (GTR 15) as an additional option to the current >23 nm methodology. In order to avoid artefacts, i.e., measuring volatile particles that have nucleated downstream of the evaporation tube, a heated oxidation catalyst (i.e., catalytic stripper) is required. This review summarizes the studies with laboratory aerosols that assessed the volatile removal efficiency of evaporation tube and catalytic stripper-based systems using hydrocarbons, sulfuric acid, mixture of them, and ammonium sulfate. Special emphasis was given to distinguish between artefacts that happened in the 10–23 nm range or below. Furthermore, studies with vehicles’ aerosols that reported artefacts were collected to estimate critical concentration levels of volatiles. Maximum expected levels of volatiles for mopeds, motorcycles, light-duty and heavy-duty vehicles were also summarized. Both laboratory and vehicle studies confirmed the superiority of catalytic strippers in avoiding artefacts. Open issues that need attention are the sulfur storage capacity and the standardization of technical requirements for catalytic strippers.

Assessment of 10-nm Particle Number (PN) Portable Emissions Measurement Systems (PEMS) for Future Regulations

The particle number (PN) emissions of vehicles equipped with particulate filters are low. However, there are technologies that can have high PN levels, especially below the currently lower regulated particle size of 23 nm. Sub-23-nm particles are also considered at least as dangerous as the larger ultrafine particles. For this reason, the European Union (EU) is planning to regulate particles down to 10 nm. In this study we compared prototype portable emission measurement systems (PEMS) and reference laboratory systems measuring from 10 nm. The tests included cycles and constant speeds, using vehicles fuelled with diesel, gasoline or liquefied petroleum gas (LPG). The results showed that the PEMS were within ±40% of the reference systems connected to the tailpipe and the dilution tunnel. Based on the positive findings and the detection efficiencies of the prototype instruments, a proposal for the technical specifications for the future regulation was drafted.

Diffusion charging measurements on exhaust solid particle number and lung deposited surface area of compressed natural gas and diesel buses

Because of their direct contact with society, urban buses are prioritized targets for air quality improvement. In this study, a sample group of in-use urban old buses powered by compressed natural gas (CNG) and diesel engines was chosen for particle emission analysis. The CNG buses do not have any type of after-treatment, while diesel ones are equipped with a diesel particulate filter (DPF). To measure the lung deposited surface area (LDSA), a possible physical metric of exhaust particles' toxicity, a diffusion charger-based analyzer was utilized. The measurements were done at different engine speeds in stationary conditions. The results revealed that although the particle mass emission of CNG buses remains at a low level, the number of emitted particles for 75% of the CNG buses (depending on their maintenance conditions) is 10 to 100 times more than the retrofitted diesel ones, with the range of 10⁶ to 10⁷ p/cm³. The rest 25% of the CNG buses were performing the same as the retrofitted diesel ones in terms of exhaust particle number in the range of 10⁵ p/cm³. In addition, the lowest LDSA parameter at low idle engine speed was measured to be 97.8 and 229.4 μm²/cm³ for a CNG and a DPF retrofitted diesel bus, respectively. This result indicates the same and even lower LDSA and surface area and thus the lower possible toxic potentiality of exhaust particles of CNG buses compared to diesel vehicles at DPF downstream. Investigation on the different behavior of the CNG buses in the emission of particles showed the correlation of some aging parameters such as lubricant oil aging mileage with the released particles and the importance of periodic maintenance interval. Graphical abstract.

Significant ultrafine particle emissions from residential solid fuel combustion

When addressing particulate matter (PM) emissions from residential solid fuel combustion, ultrafine particles are usually merged into PM_2.5, while whose mass concentration is applied as the index in evaluating PM pollution as well as assessing PM-induced health risk. This may not effectively represent the risk from ultrafine particles. In this study, we explored ultrafine particle emissions during residential combustion under both laboratory-controlled and real-world rural household conditions. Significant ultrafine particle emissions (i.e. with emission factors between 2 × 10¹⁵ to 2 × 10¹⁶ particles per kg of fuel) are found for both coal and biomass. High emissions of particle mass concentration often occur at the beginning of the combustion (i.e. the first 30 min after fire start) while high emissions of particle number concentration occur in a later combustion period (60-150 min). Ultrafine particles account for over 90% of the emitted total particle number concentration from 3 nm to 10 μm. These emissions elevate ultrafine particle number concentration by more than a decade in indoor environment under which household residents are directly exposed. In addition, we show that there is notable inconsistency between reducing PM_2.5 mass based emissions and reducing ultrafine particle number based emissions among various control strategies that were proposed for reducing pollution from residential combustion. Both "cleaner" fuels and stoves that are designed to reduce PM_2.5 emissions are found to be not necessarily effective in reducing ultrafine particle emissions, even increase their emissions in some cases. These findings indicate that the overlook of ultrafine particle emissions from residential solid fuel combustion can lead to potential health risk to household residents, especially to those vulnerable ones (e.g., the elderly and children) who are more sensitive to indoor air pollution. More attentions are needed on ultrafine particle pollution and its potential health risk in comparison to using the PM mass concentration index alone.

Comparative Study of Powertrain Hybridization for Heavy-Duty Vehicles Equipped with Diesel and Gas Engines

This article describes a study that aimed to estimate the fuel-saving potential possessed by the hybridization of conventional powertrains intended for heavy-duty vehicles based on diesel and natural gas fueled engines. The tools used for this analysis constitute mathematical models of vehicle dynamics and the powertrain, including its components, i.e., the engine, electric drive, transmission, and energy storage system (ESS). The model of the latter, accompanied by experimental data, allowed for an analysis of employing a supercapacitor regarding the selection of its energy content and the interface between the traction electric drive and the ESS (in light of the wide voltage operating range of supercapacitors). The results revealed the influence of these factors on both the supercapacitor efficiency (during its operation within a powertrain) and the vehicle fuel economy. After implementation of the optimized ESS design within the experimentally validated vehicle model, simulations were conducted in several driving cycles. The results allowed us to compare the fuel economy provided by the hybridization for diesel and gas powertrains in different driving conditions, with different vehicle masses, taking into account the onboard auxiliary power consumption.

NOx Emissions from Euro 5 and Euro 6 Heavy-Duty Diesel Vehicles under Real Driving Conditions

Despite the strengthening of vehicle emissions standards and test methods, nitrogen oxide (NOx) emissions from on-road mobile sources are not being notably reduced. The introduction of real driving emission (RDE) regulations is expected to reduce the discrepancy between emission regulations and actual air pollution. To analyze the effects of RDE regulations on heavy-duty diesel vehicles, pollutants emitted while driving were measured using a portable emission measurement system (PEMS) for Euro 5 and Euro 6 vehicles, which were produced before and after RDE regulations, respectively. NOx emissions were compared as a function of emissions allowance standards, gross vehicle weight (GVW), average vehicle speed, and ambient temperature. NOx emissions from Euro 6 vehicles were found to be low, regardless of GVW; emissions from both vehicular categories increased with a decline in the average speed. To reflect real road driving characteristics more broadly in the RDE test method for heavy-duty vehicles, it is necessary to consider engine power, which is a criterion for classifying effective sections, in the moving average window (MAW) analysis method, as well as including cold start conditions.

Evaluation of a 10 nm Particle Number Portable Emissions Measurement System (PEMS)

On-board portable emissions measurement systems (PEMS) are part of the type approval, in-service conformity, and market surveillance aspects of the European exhaust emissions regulation. Currently, only solid particles >23 nm are counted, but Europe will introduce a lower limit of 10 nm. In this study, we evaluated a 10-nm prototype portable system comparing it with laboratory systems measuring diesel, gasoline, and CNG (compressed natural gas) vehicles with emission levels ranging from approximately 2 × 10¹⁰ to 2 × 10¹² #/km. The results showed that the on-board system differed from the laboratory 10-nm system on average for the tested driving cycles by less than approximately 10% at levels below 6 × 10¹¹ #/km and by approximately 20% for high-emitting vehicles. The observed differences were similar to those observed in the evaluation of portable >23 nm particle counting systems, despite the relatively small size of the emitted particles (with geometric mean diameters <42 nm) and the additional challenges associated with sub-23 nm measurements. The latter included the presence of semivolatile sub-23 nm particles, the elevated concentration levels during cold start, and also the formation of sub-23 nm artefacts from the elastomers that are used to connect the tailpipe to the measurement devices. The main conclusion of the study is that >10 nm on-board systems can be ready for introduction in future regulations.

Solid Particle Number (SPN) Portable Emissions Measurement Systems (PEMS) in the European Legislation: A Review

Portable emissions measurement systems (PEMS) for gaseous pollutants were firstly introduced in the United States regulation to check the in-use compliance of heavy-duty engines, avoiding the high costs of removing the engine and testing it on a dynamometer in the laboratory. In Europe, the in-service conformity of heavy-duty engines has been checked with PEMS for gaseous pollutants since 2014. To strengthen emissions regulations with a view to minimise the differences between on-road and laboratory emission levels in some cases, PEMS testing, including solid particle number (SPN), was introduced for the type-approval of light-duty vehicles in Europe in 2017 and for in-service conformity in 2019. SPN-PEMS for heavy-duty engines will be introduced in 2021. This paper gives an overview of the studies for SPN-PEMS from early 2013 with the first prototypes until the latest testing and improvements in 2019. The first prototype diffusion charger (DC) based systems had high differences from the reference laboratory systems at the first light-duty vehicles campaign. Tightening of the technical requirements and improvements from the instrument manufacturers resulted in differences of around 50%. Similar differences were found in an inter-laboratory comparison exercise with the best performing DC- and CPC- (condensation particle counter) based system. The heavy-duty evaluation phase at a single lab and later at various European laboratories revealed higher differences due to the small size of the urea generated particles and their high charge at elevated temperatures. This issue, along with robustness at low ambient temperatures, was addressed by the instrument manufacturers bringing the measurement uncertainty to the 50% levels. This measurement uncertainty needs to be considered at the on-road emission results measured with PEMS.

Identification and Quantification of Uncertainty Components in Gaseous and Particle Emission Measurements of a Moped

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.

Particle Number Measurements Directly from the Tailpipe for Type Approval of Heavy-Duty Engines

The type approval of heavy-duty engines requires measurement of particulates downstream of a proportional to the exhaust flow partial flow dilution system. However, for particle number systems, which measure in real time, this is not necessary and a fixed dilution could be used. In order to assess this dilution possibility, an inter-laboratory exercise was conducted, where a “Golden” system measuring directly from the tailpipe with “hot” (150 °C) fixed dilution was compared with the laboratory regulated systems. Additional “Golden” counters were measuring from 10 nm, below the current cut-off size of 23 nm defined in the regulation, in order to collect data below 23 nm and to confirm that the direct sampling is also possible for smaller sizes. Seven diesel engines and two CNG (compressed naturals gas) engines were used in six laboratories. The results of the “Golden” instruments were within 25% in most cases, reaching 40% in two laboratories for both >23 nm and >10 nm. The repeatability of the measurements (10% to 40%) remained the same for both systems with both cut-off sizes. One test with regeneration showed clear difference between the 10 nm systems, indicating that the thermal pre-treatment only with evaporation tube might not be adequate. Another system measuring from the tailpipe with a fixed “cold” (at ambient temperature) dilution gave differences of up to 50% in most cases (on average +26%). Dedicated tests with this system showed that the differences were the same with fixed or proportional dilution, indicating that it is not the concept that resulted in the overestimation, but the calibration of the system. The main conclusion of this study is that direct sampling with fixed dilution from the tailpipe can be introduced in the future regulation.

Exhaust Gas Condensation during Engine Cold Start and Application of the Dry-Wet Correction Factor

Gas components, like carbon monoxide (CO) and dioxide (CO2), can be measured on a wet- or dry-basis depending on whether the water is left or removed from the sample before analysis. The dry concentrations of gaseous components in the exhaust from internal combustion engines are converted to wet concentrations with conversion factors based on the combustion products and the fuel properties. Recent CO2 measurements with portable emissions measurement systems (PEMS) compared to laboratory grade equipment showed differences during the first minutes after engine start. In this study we compared instruments measuring on a dry- and wet-basis using different measuring principles (non-dispersive infrared detection (NDIR) and Fourier-transform infrared spectroscopy (FTIR)) at the exhaust of gasoline, compressed natural gas (CNG), and diesel light-duty and L-category vehicles. The results showed an underestimation of the CO2 and CO mass emissions up to 13% at cold start when the conversion factor is applied and not direct “wet” measurements are taken, raising concerns about reported CO2 and CO cold start emissions in some cases. The underestimation was negligible (<1%) for CO2 when the whole test (20–30 min) was considered, but not for CO (1%–10% underestimation) because the majority of emissions takes place at cold start. Exhaust gas temperature, H2O measurements and different expressions of the dry-wet corrections confirmed that the differences are due to condensation at the exhaust pipes and aftertreatment devices when the surface temperatures are lower than the dew point of the exhaust gases. The results of this study help to interpret differences when comparing instruments with different principles of operation at the same location, instruments sampling at different locations, or the same instrument measuring different driving test cycles or at different ambient temperatures (e.g., −7 °C).

Experimental Assessment of an Electrofilter and a Tandem Positive-Negative Corona Charger for the Measurement of Charged Nanoparticles formed in Selective Catalytic Reduction Systems

Onboard measurement of non-volatile particle number (PN) emissions with portable emissions measurement systems (PEMS) was introduced for the type-approval of passenger cars in Europe since 2017 and is foreseen for heavy-duty (HD) vehicles in 2021. First studies on the performance of PN-PEMS with HD engine exhaust revealed larger differences between established PN-PEMS techniques than what was observed for passenger cars. Particles forming in selective catalytic reduction (SCR) systems for NOx of late technology HD engines have recently been identified as a potential reason for the observed differences. The formed particles have a size distribution peaking below the regulatory limit of 23 nm and most importantly acquire high (more than one) positive charges at the elevated exhaust temperatures. Precise measurement of such highly charged nanosized particles with PN-PEMS instrumentation utilizing diffusion charger (DC) based counters requires proper conditioning of these charges. Two approaches were investigated in this study: (a) an electrofilter (EF) to completely remove charged particles below the regulated size and (b) a tandem negative-positive corona (TC) charger to directly condition pre-charged particles. The two technical solutions were tested alongside the unmodified DC-based PN-PEMS, a PN-PEMS utilizing a condensation particle counter (CPC) and a reference stationary PN system using exhaust of two SCR-equipped HD engines. The results confirmed that the particles forming in such SCR systems are responsible for the observed inconsistencies and that both technical solutions efficiently address the interferences of these pre-charged nanoparticles.

Emission Factors of a Euro VI Heavy-duty Diesel Refuse Collection Vehicle

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 (NOx, 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 NOx 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): NOx < 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.

Fuel Switch to LNG in Heavy Truck Traffic

Liquefied natural gas (LNG) use as a fuel in road and maritime traffic has increased rapidly, and it is slowly entering railroad traffic as well. The trend was pushed by the state administrations of mainly EU countries and international organizations seeing LNG as a cost-effective and environmentally friendly alternative to diesel. Different infrastructural projects for the widespread use of LNG in transport have been launched around the world. The main goal of this paper was to analyze use of LNG as a fuel for heavy trucks. Different aspects of LNG chain were analyzed along with economical and ecological benefits of LNG application. Filling stations network for LNG were described for the purpose of comparative analysis of diesel and LNG heavy trucks. Conclusion has shown that using LNG as propellant fuel has numerous advantages over the use of conventional fuels. The higher initial investment of the LNG road vehicles could be amortized in their lifetime use, and in the long-term they are more affordable than the classic diesel vehicles. In addition to cost-effectiveness, LNG road vehicles reduce CO2 emissions. Therefore, the environmental goals in transport, not only of the member states but worldwide, could not be met without LNG in heavy truck traffic.

Evaluation of NOx emissions of a retrofitted Euro 5 passenger car for the Horizon prize "Engine retrofit"

The Horizon 2020 prize for the "Engine Retrofit for Clean Air" aims at reducing the pollution in cities by spurring the development of retrofit technology for diesel engines. A Euro 5 passenger car was retrofitted with an under-floor SCR (Selective Catalytic Reduction) for NO_x catalyst in combination with a solid ammonia based dosing system as the NO_x reductant. The vehicle was tested both on the road and on the chassis dynamometer under various test cycles and ambient temperatures. The NO_x emissions were reduced by 350-1100 mg/km (60-85%) in the laboratory depending on the test cycle and engine conditions (cold or hot start), except at type approval conditions. The reduction for cold start urban cycles was < 75 mg/km (< 15%). The on road and laboratory tests were inline. In some high speed conditions significant increase of ammonia (NH₃) and nitrous oxide (N₂O) were measured. No effect was seen on other pollutants (hydrocarbons, carbon monoxide and particles). The results of the present study show that retrofitting high emitting vehicles can significantly reduce vehicle NO_x emissions and ultimately pollution in cities.