Conference report: 5th BOSMAL Emissions Symposium
30 May 2016
The 5th International Exhaust Emissions Symposium organized by BOSMAL Automotive Research & Development Institute was held on May 19-20, 2016 at the BOSMAL facilities in Bielsko-Biała, Poland. The conference program included 25 presentations and a poster session on topics including vehicle emission regulations and new EU testing procedures, emission control technologies, emission measurement, and fuel and lubricant developments. The symposium was attended by about 130 participants.
Emission Regulations. Several talks in the session on emission regulations were inspired by the introduction of Real Driving Emission (RDE) testing requirements in the EU (Euro 6d emission standards) and the apparent weakness of the EU compliance model with emission standards, as demonstrated by the Volkswagen diesel emission scandal. The session was open by Piotr Bielaczyc (Bosmal) who discussed the history of automotive emission regulations in the United States, European Union, China and India, and identified some of the problem areas in EU emission regulations—high in-use NOx emissions from diesel cars, PM emissions from gasoline direct injection (GDI) engines, and real life CO2 emission levels that are significantly higher than the regulatory NEDC test values. The diesel NOx and GDI PM emission issues are expected to be solved by the coming RDE testing requirements and by the particle number (PN) emission limits for GDI vehicles, respectively. The high real life CO2 issue, on the other hand, has no apparent solution. The growing gap between the NEDC test cycle results and real life emissions—now at 30-50%—is not likely to be adequately addressed by the new WLTC test cycle, as CO2 emissions over NEDC and WLTC do not differ significantly.
A comparison of emission standard design and enforcement approaches in the EU and in the USA was presented by the ICCT [V. Franco]. Some of the key elements of an effective compliance program include representative type approval procedures, compliance testing of new and in-use vehicles, vehicle recalls and financial penalties, and adequate government resources with enforcement agencies insulated from political influence. In the EU, several of these components are missing. There is no EU-level authority responsible for vehicle type approvals or enforcement of emission regulations—both of these critical functions are delegated to the member states. There is no mechanism for a EU-wide vehicle recall. Emission recalls—which are very uncommon—can be only initiated in the country that issued the type approval, by the local type approval agency. Another weakness of the EU regulations is the ambiguity in the definition of emission control systems and defeat devices (as a consequence, it has not yet been determined whether the VW test cycle beating software represents a violation of the EU emission regulations or not). The coming changes to the type approval framework and the RDE regulation will make the EU system stronger. However, some problems will likely persist—for instance, there is still no political will to create a central EU authority for type approvals.
The first package of RDE measures was recently published as the Commission Regulation (EU) 2016/427 [Helge Schmidt, TÜV Nord]. The RDE testing, which will be phased-in for new type approvals from September 2017 (with a NOx conformity factor of 2.1) through January 2020 (CF = 1.5), requires testing vehicles on the road using Portable Emission Measurement Systems (PEMS). The RDE route includes equal portions of urban, extra-urban and motorway driving. The route used for RDE tests by Germany’s TÜV Nord is 83 km long, and the test takes about 105 minutes. Two tools are used for data evaluation: the moving average window (MAW) method developed by the JRC and the power bin method (SPF) by the TU Graz. Open issues with RDE testing include cold start emissions—whether to measure them separately or to include them in the whole test—and how to test hybrid vehicles.
Kurt Engeljehringer [AVL List] discussed global trends in emission regulations and their impact on emission testing methods and equipment. AVL evaluated the RDE testing procedures and conducted experimental RDE tests, which included PEMS validation for accuracy on a dyno, a road run, and another test on the dyno. The RDE test could determine NOx emissions with an accuracy of ±28%. Another coming change in vehicle testing is the adoption of the WLTC test, which will replace NEDC. The WLTC, described in the UNECE Global Technical Regulation (GTR) 15, will be also adopted by other countries, including Japan and Korea. China, who traditionally followed EU emission standards, is considering emission regulations more stringent than Euro 6. The proposed China 6a standards are based on Euro 6 limits, but with a fuel neutral approach. The proposed China 6b limits are 50% below Euro 6—if the proposals are adopted, by 2020 China could have the most stringent light-duty vehicle emission standards in the world. A summary of vehicle emission testing regulations and methods around the world can be found in the AVL Emission Testing Handbook. The talk also included a selection of interesting emission test results performed in Europe in connection with the VW emission scandal. The test results strongly suggest that control software is the main driver behind emissions from European cars. Different vehicle models often show inconsistent emission trends and in many cases—including vehicles with SCR aftertreatment—hot start NEDC emissions are higher than cold start results, even though the catalyst temperature is higher. Euro 5/6 regulations prohibit high in-use emissions, but include an exemption where the emission system is deactivated for the protection of the engine (for example, EGR can be deactivated at low temperatures to prevent condensation and corrosion in the EGR cooler). It would appear that vehicle manufacturers use the engine protection exemption gratuitously. Under the EU regulations, engine protection exemptions do not have to be reported and can be used at the discretion of the manufacturer. In contrast, in the United States manufacturers must receive a regulatory approval for all instances when emission components become deactivated (so-called Auxiliary Emission Control Device, AECD).
Giovanni D'Urbano [FOEN, Switzerland] summarized the Swiss approach to regulating pollutant emissions and greenhouse gases. Switzerland generally adopts EU regulations, but in some cases the requirements are more stringent. For instance, Switzerland has had a particle number emission limit, in addition to the EU PM mass limit, for construction machinery. To meet the PN limit, construction machines in Switzerland must be equipped with diesel particulate filters (DPF). In their in-use DPF testing program, Switzerland is phasing-out opacity meters and introducing particle number instruments. Two PN instruments have been approved, one from TSI and one from Testo. Talking about GHG emissions, the speaker emphasized that engine efficiency improvements may be close to limits and other strategies—for instance power-to-liquid fuels—are necessary if further CO2 emission reductions from transportation are desired.
Emission Reduction. The session on emission reduction technologies opened with an overview of emerging trends in engines and aftertreatment by Tim Johnson [Corning]. Significant improvements in engine efficiency have been reported, with gasoline engines reaching 45% brake thermal efficiency (BTE). Further progress in gasoline engine efficiency is still possible, but increments in diesel BTE may come at a lower cost. In spite of the improving BTE, meeting the US EPA 2025 GHG targets for light-duty vehicles remains very challenging—the rate of fuel economy improvement, which was about 3% per year over 2005-2015, would have to triple to meet the 2025 emission targets. One of the most promising emerging engine technologies are 2-stroke opposed piston engines. Emission aftertreatment technologies that have seen ongoing development include urea SCR and SCR on filter (SCRF), passive NOx adsorbers (PNA), methane oxidation catalysts, and gasoline particulate filters (GPF). A noteworthy feature of the GPF technology is its ability to control PAH emissions that can otherwise pass through the three-way catalyst.
Hybrid powertrains are expected to be widely used to meet future GHG emission mandates. In the case of plug-in hybrids (PHEV), a small battery can provide a significant displacement of petroleum. However, PHEV testing to determine the reductions in fuel consumption is not a trivial task [Mike Douba, Argonne National Laboratory]. There are two testing modes with largely different fuel consumption: a charge sustaining mode, and a charge depleting mode. The real operation is an unknown mix of the two modes, resulting in a large uncertainty in fuel economy.
Claus Görsmann [Johnson Matthey] presented an interesting look at future low carbon powertrain options. It was predicted that diesel, which can provide a 15% fuel consumption benefit over gasoline, must remain an important powertrain option in order to meet the GHG reduction targets. While more diverse powertrains will evolve, with more electrification, in 2025 97% of vehicles will still have an IC engine. The long term picture is rather concerning, due to the lack of progress in reducing our massive GHG emissions. Based on the UN IPCC models, if carbon emission rates continue at the current level, the planet can warm by 2°C by 2038, which leaves little time for the technology change to decarbonize transportation. In the case of IC diesel and gasoline engines, the necessary technologies include bio- and electro-fuels produced using low carbon energy. In the case of electric and PHEV vehicles, low carbon electricity—renewable or nuclear—would be necessary to reduce emissions.
Emission Characterization and Measurement. Will Northrop [University of Minnesota] discussed semi‐volatile particulate matter emissions from conventional diesel combustion and from low temperature combustion (LTC) modes, including PCCI and RCCI. Experiments were conducted on a light- and a medium-duty engine, using gasoline and hydrous ethanol as the fumigant for the RCCI mode. It was found that LTC decreased soot, but increased CO, HC and semi-volatiles. The nucleation of semi-volatile particles occurred via a sulfur mechanism, even though the sulfur content of the fuel was only 11 ppm. Another emission study [T. Ronkko, Tampere University of Technology] investigated particle emissions from natural gas engine exhaust. Particle number emissions were dominated by particles below 10 nm in diameter, which were volatile but included solid cores that were thought to originate from lube oil metals or heavy-hydrocarbons.
Traffic congestion could be a major cause of high real driving emissions from both diesel and gasoline vehicles, and a source of elevated ambient pollutant concentrations [Gordon Andrews, University of Leeds]. RDE emissions from a Euro 4 SI vehicle were analyzed and correlated with ambient air quality data from a monitoring station located next to a busy highway section in Leeds, UK. It was concluded that air quality exceedances for PM and NO2 can be linked to traffic congestion. In congested traffic, the average speed is low, peak accelerations are high and the number of accelerations from idle per km is much higher than on any test cycle. These are the reasons for real world driving causing poor air quality in cities, according to the study. Congested traffic conditions, however, are ignored in the new WLTC and RDE tests. Thus, these new test procedures will not address the issue of real world driving and poor urban air quality. The significance of congested traffic extends to heavy-duty vehicles as well. RDE tests of a heavy truck with urea-SCR system on a congested road showed that emissions occurred specifically during stop/start events and that emissions correlated with the average velocity. If velocity was extrapolated to that of the test cycle, the emissions decreased to the regulatory limit.
William Silvis [AVL North America] discussed gravimetric measurements of particulate matter emissions at low PM levels, corresponding to the 2025 California LEV III PM limit of 1 mg/mi. Data was presented that illustrated the impact of a number of variables and phenomena (nucleation, SOF adsorption, artifacts) and the implications on filter accuracy and repeatability. It was concluded that the current regulatory PM filter method can be used as a “pass/fail” metric at PM levels as low as 0.5 mg/mi. Dekati [M. Moisio] presented their eFilter gravimetric PM filter holder with an integrated miniature diffusion charger, that provides both standard gravimetric PM results and real-time information about PM accumulation on the filter. The eFilter provides fast response real time signal, with second-by-second data. At low emission levels, the eFilter signal is more repeatable and more sensitive than the gravimetric weighing result.
As particle number emission limits are to be added to the regulatory RDE requirements, test equipment manufacturers have been developing PN units to be added to the gas PEMS package. Sensors Europe [M. Heuser] developed a particle counter based on the mixing CPC principle, where the sampled particles are mixed with air saturated with butanol. A catalytic stripper is used in place of the PMP volatile particle remover (VPR). Measurements using the Sensors CPC correlated well with those using TSI CPC.
Fuels and Lubes. Current transportation fuels may not be adequate for future powertrain options—such as low temperature combustion—and may constrain engine design. In October 2015, the US Department of Energy (DOE) launched the Co-Optima project (Co-Optimization of Fuels & Engines) with the aim of accelerating the introduction of affordable, scalable, and sustainable biofuels and high-efficiency, low-emission vehicle engines [T. Wallner, Argonne National Laboratory]. One of the early tasks of the project is to identify molecules and pathways to enable future fuels, with a focus on liquid fuels compatible with the existing infrastructure. A long term goal of the project is to improve passenger vehicle fuel economy by 50%, 15%–20% beyond the projected results of existing R&D efforts, and to accelerate the rate of advanced biofuels deployment.
Methanol is a liquid fuel that could be used to bridging the gap to the hydrogen economy [K. Skaardalsmo, Skaardalsmo Fuel Consulting]. Methanol is the most efficient hydrogen carrier due to its lowest C:H ratio among all liquid fuels. While methanol is typically manufactured from natural gas, it can be made from renewable resources, such as from recycled CO2 and hydrogen from water electrolysis. Methanol can be reformed into CO + H2 at the exhaust gas temperature using a catalyst, to produce gas mixture of increased energy content. In China, methanol (made from coal and used as M10 or M15) contributes to 8% of gasoline consumption.
Presentations on lube oil topics included a talk by BASF [T. Hartmann] discussing an experimental study on the impact of soot formation on lubricant aging in DISI engines, and by Petronas [G. Cecconello] on the development of a low viscosity, SAE 0W-20 lube oil for heavy-duty engines.
After the symposium, the participants could take part in a tour of Bosmal testing facilities, which include vehicle and engine emission test cells, as well as a range of state-of-the-art equipment and instruments for testing of vehicles and vehicle components, materials, electronic tests and metrology measurements.