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The subject of exhaust particulate emissions from road vehicles continues to gain attention and further, more stringent legislative demands are expected in this area. While the European Union has been at the forefront in recent decades, other jurisdictions are making progress towards more comprehensive control and limitation of exhaust particulate. This technical overview examines past, current and likely future (Euro 7) legislative requirements and also presents sample results from a range of vehicle types, in order to make comparisons and discuss the impact of expected regulatory updates. The impacts of powertrain trends, including hybridization, on exhaust particulate emissions and their control are briefly analyzed. Regulatory trends including the intention to move the lower boundary of the size range considered from 23 nm to 10 nm and the elimination of fuel- and technology-specific limits on particulate emissions are discussed and their implications analyzed.

Exhaust gas aftertreatment systems can, under certain conditions, create undesired chemical species as a result of their elimination reactions. A prime example of this is ammonia (NH3), which is not formed in the combustion reaction, but which can be formed within a three-way catalyst (TWC) when physicochemical conditions permit. The elimination of NOx in the TWC thus sometimes comes at the cost of significant emissions of NH3. Ammonia is a pollutant and a reactive nitrogen compound (RNC) and NH3 emissions should be analyzed in this context, alongside other RNC species. Examination of the literature on the subject published over the past two decades shows that ammonia, a species which is currently not subject to systematic emissions requirements for road vehicles in any market, is often identified as forming the majority of the RNC emissions under a range of operating conditions.

For over a decade, the EU has required in-service conformity testing of heavy-duty road vehicles. This paper briefly discusses the practical aspects of the test requirements, how they have evolved and how they compare to other precedents, such as the heavy-duty engine dynamometer-based type approval testing procedure, as well as broadly equivalent EU requirements for light duty vehicles. Emissions requirements for heavy-duty vehicles are work-specific, but based on standard test results a range of other parameters can be calculated to yield distance-specific, tonnage-distance specific, CO2-specific and (gravimetric) fuel-specific results. At present, CO2 and fuel consumption are not subject to any limits per se during on-road testing (and this is the case for both heavy and light duty vehicles); nevertheless, the aforementioned parameters must be measured and such results can be of interest for a variety of reasons.

This paper discusses the legislative situation regarding type approval of plug-in hybrid vehicles (also known as off-vehicle charging hybrid-electric vehicles, OVC-HEV) in the range of exhaust emissions and fuel consumption. A range of tests were conducted on two Euro 6d-complaint OVC-HEVs to quantify emissions. Procedures were based on EU legislative requirements. For laboratory (chassis dyno) testing, two different test cycles and three different ambient temperatures were used for testing. Furthermore, in some cases additional measurements were performed, including measurement of emissions of particulate matter and continuous analysis of regulated and unregulated pollutants in undiluted exhaust. Consumption of electrical energy was also monitored. On-road testing was conducted on the test vehicle tested on the chassis dyno in the tests mentioned above, as well as on a second OVC-HEV test vehicle.

Despite an overall trend towards harmonization in vehicle regulations, regional differences persist in the area of exhaust emissions and fuel economy. The test procedure employed can exert a significant impact on the results obtained. In this paper, the EU and US type approval procedures for light duty vehicles are briefly compared and results obtained from several types of test procedure are presented. Specifically, emissions tests were performed on a single SUV which met US Tier III emissions limits. The vehicle featured a conventional, naturally aspirated spark ignition engine with indirect fuel injection and an aftertreatment system consisting of three-way catalysts with no dedicated particulate filtration device. The vehicle’s engine displacement, total mass and power-to-mass ratio were relatively representative of the upper end of the US market, but represented an outlying vehicle in terms of the characteristics of the EU fleet.

The selective catalytic reduction (SCR) of nitrogen oxides by ammonia is commonly applied as a method of exhaust aftertreatment for lean burn compression ignition (CI) engines. The catalytic reactor of an SCR system, like all catalytic emission control devices, is susceptible to partial deactivation as its operating time progresses. Long-term exposure of an SCR reactor to exhaust gas of fluctuating temperature and composition results in variations of the characteristics of its catalytically active layer. The aim of this study was to observe and investigate the variation of parameters characterizing the SCR reactor as a result of its ageing. Attention was paid to changes in ammonia storage capacity, selectivity of chemical reactions and maximum achievable NOx conversion efficiency. The experimental setup was a heavy duty (HD) Euro VI-compliant engine and its aftertreatment system (ATS). The setup was installed on a transient engine dyno instrumented with emission measurement devices.

Particle number (PN) emission limits were introduced in the European Union’s regulations for light-duty and heavy duty vehicles in the years 2011-2014. Since then, PN measurements have become a common practice in the automotive sector. Many studies showed that the current methodology, which counts particles >23 nm, misses a large fraction of particles for some engine technologies, such as port fuel injection vehicles or vehicles fueled with compressed natural gas (CNG). However, data for the latest technology vehicles are lacking. For this reason, we measured PN emissions >23 nm and >10 nm of >30 CNG, gasoline and diesel-fueled vehicles. Two systems were measuring in parallel from the full dilution tunnel; one with an evaporation tube and the other with a catalytic stripper. The PN emission levels spanned over three orders of magnitude depending on whether there was a particulate filter installed or not.

The aim of this paper is to analyse the results of regulated and unregulated emissions and carbon dioxide (CO2) emissions of passenger cars equipped with compression-ignition engines that meet the emission Euro 6d standards. Both test vehicles featured selective catalytic reduction (SCR) systems for control of oxides of nitrogen (NOx) and one vehicle also featured a passive NOx absorber (PNA). Research was performed using the current European Union exhaust emission test methods for passenger cars (Worldwide harmonized Light vehicles Test Procedures (WLTP)). Emission testing was performed on a chassis dynamometer, within a climatic chamber, at two different ambient temperatures: 23°C (i.e. Type I test) and -7°C (known as a Type VI test - currently not required for this engine type according to EU legislative requirements).

Non-plugin hybrids represent a technology with the capability to significantly reduce fuel consumption (FC), without any changes to refuelling infrastructure. The EU market share for this vehicle type in the passenger car segment was 3% in 2018 and this powertrain type remains of interest as an option to meet the European Union (EU) fleet average CO2 limits. EU legislative procedures require emissions limits to be met during the chassis dynamometer test and in the on-road real driving emissions (RDE) test, while official CO2/FC figures are quantified via the laboratory chassis dynamometer test only. This study employed both legislative test procedures and compared the results. Laboratory (chassis) dynamometer testing was conducted using the Worldwide Harmonised Light Vehicles Test Procedure (WLTP). On-road testing was carried out in accordance with RDE requirements, measuring the concentration of regulated gaseous emissions and the number of solid particles (PN).

The aim of this paper was to describe a method of accelerated three way catalytic converter (TWC) ageing performed on the engine test bed for European On Board Diagnostics (EOBD) monitoring purposes and screening of different catalysts solutions. To accelerate the catalyst ageing process, the exhaust gas temperature was elevated to a range 1000 - 1200°C, which is typical for an ageing cycle performed using ovens. Catalyst emissions performance was checked at new condition (after degreening) and subsequently at predefined ageing intervals, based on the oxygen storage capacity (OSC) evaluation. The emission tests were performed in the laboratory on the chassis dynamometer using legislative cycles. The accelerated ageing method was found to be of use for verifying the EOBD functionality under vehicle operation with a degraded catalyst substrate.

European Union RDE (real driving emissions) legislation requires that new vehicles be subjected to emissions tests on public roads. Performing emissions testing outside a laboratory setting immediately raises the question of the impact of ambient conditions - especially temperature - on the results. In the spirit of RDE legislation, a wide range of ambient temperatures are permissible, with mathematical moderation (correction) of the results only permissible for ambient temperatures <0°C and >+30°C. Within the standard range of temperatures (0°C to +30°C), no correction for temperature is applied to emissions results and the applicable emissions limits have to be met. Given the well-known link between the thermal state of an engine and its emissions following cold start, ambient temperature can be of great importance in determining whether a vehicle meets emissions requirements during an RDE test.

This paper discusses the importance of the inclusion of emissions from the cold start event during legislative on-road tests on passenger cars (RDE - real driving emissions tests conducted under real-world driving conditions, as defined by EU legislation). Results from a recently-registered gasoline-powered vehicle are presented, with the main focus on the comparison of exhaust emission results: excluding/including the cold start during the initial phase of the RDE test. Cold start is the most challenging aspect of emissions control for vehicles with spark ignition engines and the inclusion of the cold start event in RDE test procedure has wide-ranging implications both for the testing process and compliance with RDE legislation via optimisation of aftertreatment systems and the engine calibration. In addition to some theoretical arguments, the results of an RDE-compliant test performed using the aforementioned procedures are presented.

In this study, two vehicles were tested under real driving conditions with gaseous exhaust emissions measured using a portable emissions measurement system (PEMS). One of the vehicles featured a hybrid powertrain with a spark ignition internal combustion engine, while the other vehicle featured a non-hybrid (conventional) spark ignition internal combustion engine. Aside from differences in the powertrain, the two test vehicles were of very similar size, weight and aerodynamic profile, meaning that the power demand for a given driving trace was very similar for both vehicles. The test route covered urban conditions (but did include driving on a road with speed limit 90 km/h). The approximate test route distance was 12 km and the average speed was very close to 40 km/h.

This paper reports testing conducted on multiple vehicle types over two European legislative driving cycles (the current NEDC and the incoming WLTC), using a mixture of legislative and non-legislative measurement devices to characterise the particulate emissions and examine the impact of the test cycle and certain vehicle characteristics (engine/fuel type, idle stop system, inertia) on particulate emissions. European legislative measurement techniques were successfully used to quantify particle mass (PM) and number (PN); an AVL Microsoot sensor was also used. Overall, the two driving cycles used in this study had a relatively limited impact on particulate emissions from the test vehicles, but certain differences were visible and in some cases statistically significant.

Concern over greenhouse gas (GHG) emissions and air quality has made exhaust emissions from passenger cars a topic interest at an international level. This situation has led to the re-evaluation of testing procedures in order to produce more “representative” results. Laboratory procedures for testing exhaust emissions are built around a driving cycle. Cycles may be developed in one context but later used in another: for example, the New European Driving Cycle (NEDC) was not developed to measure fuel consumption, but has ended up being used to that end. The new Worldwide harmonized Light vehicles Test cycle (the WLTC) will sooner or later be used for measuring regulated exhaust emissions. Legal limits for emissions of regulated pollutants are inherently linked to the test conditions (and therefore to the driving cycle); inter-cycle correlations for regulated pollutants are an important research direction.

This paper presents a study of passenger cars in terms of emissions measurements in tests conducted under real driving conditions (RDE - Real Driving Emissions) by means of PEMS (Portable Emission Measurement System) equipment. A special feature of the RDE tests presented in this paper is that they were performed under Polish conditions and the specified parameters may differ from those in most other European Union countries. Emission correction coefficients have been defined, based on the test results, equal to the increase (or decrease) of driving emissions during the laboratory (‘chassis dyno’) test or during normal usage in relation to the EU emission standards (emission class) of the vehicle.

Particulate matter in vehicular exhaust is now under great scrutiny. In the EU, direct injection spark ignition (DISI) engines running on petrol now have limits for particulate emissions set for both mass and number. Current legislative test procedures represent a best-case scenario - more aggressive driving cycles and lower ambient temperatures can increase particulate emissions massively. Ambient temperature is generally the environmental parameter of most importance regarding particulate emissions from an engine, particularly for the reasonably brief periods of operation typical for passenger cars operating from a cold start. Two Euro 5 vehicles with DI SI engines were laboratory tested at three ambient temperatures on two different commercially available fuels, with particulate emissions results compared to results from the same fuels when the vehicles were tested at 25°C.

The aim of this paper was to explore the influence of CNG fuel on emissions from light-duty vehicles in the context of the new Euro 6 emissions requirements and to compare exhaust emissions of the vehicles fueled with CNG and with gasoline. Emissions testing was performed on a chassis dynamometer according to the current EU legislative test method, over the New European Driving Cycle (NEDC). Additional tests were also performed on one of the test vehicles over the World Harmonized Light Vehicles Test Cycle (WLTC) according to the Global Technical Regulation No. 15 test procedure. The focus was on regulated exhaust emissions; both legislative (CVS-bag) and modal (continuous) analyses of the following gases were performed: CO (carbon monoxide), THC (total hydrocarbons), CH4 (methane), NMHC (non-methane hydrocarbons), NOx (oxides of nitrogen) and CO2 (carbon dioxide).

Due to concern over emissions of greenhouse gases (GHG; particularly carbon dioxide - CO2), energy consumption and sustainability, many jurisdictions now regulate fuel consumption, fuel economy or exhaust emissions of CO2. Testing is carried out under laboratory conditions according to local or regional procedures. However, a harmonized global test procedure with its own test cycle has been created: the World Harmonized Light Vehicles Test Cycle - WLTC. In this paper, the WLTC is compared to the New European Driving Cycle (NEDC) and the FTP-75 cycle used in the USA. A series of emissions tests were conducted at BOSMAL on a chassis dynamometer in a Euro 6-complaint test facility to determine the impact of the test cycle on CO2 emissions and fuel consumption. While there are multiple differences in the test cycles in terms of dynamicity, duration, distance covered, mean/maximum speed, etc, differences in results obtained over the three test cycles were reasonably limited.

Ethanol has a long history as an automotive fuel and is currently used in various blends and formats as a fuel for spark ignition engines in many areas of the world. The addition of ethanol to petrol has been shown to reduce certain types of emissions, but increase others. This paper presents the results of a detailed experimental program carried out under standard laboratory conditions to determine the influence of different quantities of petrol-ethanol blends (E5, E10, E25, E50 and E85) on the emission of regulated and unregulated gaseous pollutants and particulate matter. The ethanol-petrol blends were laboratory tested in two European passenger cars on a chassis dynamometer over the New European Driving Cycle, using a constant volume sampler and analyzers for quantification of both regulated and unregulated emissions.