Search Results

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.

In this study, tailpipe-sampling was used to sample the exhaust aerosol of a Stage IV tractor equipped with Diesel Oxidation Catalyst (DOC) and Selective Catalytic Reduction (SCR) aftertreatment systems. The particle emissions were characterized in terms of number concentration (particle size of > 2.5 nm), mass concentration (particle size of 6-612 nm) BC mass concentration and chemical composition (particle size of > 30 nm). The measurements were conducted on-road by setting a mobile laboratory on a trailer and pulling it with the tractor. In addition to driving, heavy-lift work cycles were tested, where separate lifts of a 1000 kg weight were conducted with the front fork of the tractor with two minutes of idling between consecutive lifts. Both a Porous Tube Diluter (PTD) with ambient temperature dilution air as well as an ejector diluter with hot dilution air were used to sample the exhaust aerosol.

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.

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 latest generation of internal combustion engines may emit significant levels of sub-23 nm particles. The main objective of the Horizon 2020 “DownToTen” project was to develop a robust methodology and provide policy recommendations towards the particle number (PN) emissions measurements in the sub-23 nm region. In order to achieve this target, a new portable exhaust particle sampling system (PEPS) was developed, being capable of measuring exhaust particles down to at least 10 nm under real-world conditions. The main design target was to build a system that is compatible with current PMP requirements and is characterized by minimized losses in the sub-23 nm region, high robustness against artefacts and high flexibility in terms of different PN modes investigation, i.e. non-volatile, volatile and secondary particles.

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.

Particle number emissions from an off-road diesel engine without exhaust after-treatment were studied by using five different heavy-duty lubricating oils in the engine. The study extends understanding on how the properties of lubricating oil affect the nanoparticle emissions from an off-road diesel engine. The lubricants were selected among the performance classes of the European Automobile Manufacturers Association, at least one lubricant from each category intended for heavy-duty diesel engines. Particle size distributions were measured by the means of an engine exhaust particle sizer (EEPS), but soot emissions, gaseous emissions and the basic engine performance were also determined. During the non-road steady state cycle, the most of the differences were detected at the particle size range of 6-15 nm. In most cases, the lowest particle quantities were emitted when the highest performance category lubricant was used.

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.

In this article we present a design of a new miniaturized sensor with the capacity to measure exhaust particle concentrations on board vehicles and engines. The sensor is characterized by ultra-fast response time, high sensitivity, and a wide dynamic range. In addition, the physical dimensions of the sensor enable its placement along the exhaust line. The concentration response and temporal performance of a prototype sensor are discussed and characterized with aerosol laboratory test measurements. The sensor performance was also tested with actual engine exhaust in both chassis and engine dynamometer measurements. These measurements demonstrate that the sensor has the potential to meet and even exceed any requirements around the world in terms of on-board diagnostic (OBD) sensitivity and frequency of monitoring.

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.