Despite the continuing and significant reductions in the legislated limits of light-duty diesel vehicle NOx emissions under the European Euro 1 through 5 regulations of recent years, many studies have demonstrated that real-world NOx emissions appear not to have been reduced as significantly. The Volkswagen emissions scandal has certainly spotlighted this issue, but more by the intentionality of the cause rather than by the effect.
This divergence between type-approval limits and real world emissions was one of the primary drivers for the proposed introduction of Real Driving Emissions (RDE) (earlier post)—put forward in the European Commission’s CARS 2020 Action Plan (earlier post)—in European Euro 6c legislation as early as 2017. The objective of this proposed regulation is that future vehicles certified to a given type approval threshold for NOx output will, subject an incremental Conformity Factor to be defined in the regulation, not exceed this level in normal on-road driving conditions.
A core aspect of the introduction of RDE testing is on-road vehicle testing using a Portable Emissions Measurement System (PEMS) in combination with post-processing of the results to include the evaluation of real driving NOx and CO2 emissions. While the full and final details of RDE regulations are yet to be fully defined, it is understood that reduction of NOx emissions will be required across a wider spectrum of engine operating conditions than those of the Euro 5 rules.
In this context, Ricardo says that it is essential to establish a development process that is capable of providing cost-effective yet RDE-compliant powertrain and aftertreatment solutions.
In an extensive and ongoing research project, the initial results of which were reported at the JSAE Annual Congress earlier this year, Ricardo has demonstrated processes for evaluating the emission technologies of diesel cars under the forthcoming RDE regulations.
While planning its RDE research, Ricardo aimed to couple its practical experience of PEMS testing with its vehicle simulation capabilities in order to enable assessment of different vehicle and aftertreatment systems over a compliant RDE cycle. This approach enabled a detailed review of the NOx control performance of the engine and aftertreatment systems of each different vehicle configuration, and allowed an evaluation of the Conformity Factor. This was generated by analysis using the proposed EMROAD and CLEAR data reduction algorithms to assess the PEMS test results. Finally the project aimed to study the key contributing factors for RDE results in order to further refine the future development process.
Ricardo’s Shoreham Technical Center provides a suitable location for the type of mixed driving that is considered likely to form the basis of RDE regulations, including rural, urban, and fast highway roads, and a range of gradients. As such, Ricardo was able to define an RDE route comprising all of the likely requirements within a 20 km (12.4 mile) radius of the company’s technical center.
Each engine-vehicle configuration was simulated over the NEDC and WLTC cycles in order to provide input to the data reduction tools, and the working assumption for legislated NOx limit used was 80 mg/km. Two vehicles were used as the basis of the study; a typical C-segment hatchback and a mid-sized European SUV. Within these two classes, a range of aftertreatment technologies was assessed for each vehicle in order to assess its likely Conformity Factor under projected RDE requirements.
Laboratory based testing of the research vehicles was carried out in the Ricardo Vehicle Emissions Research Center (VERC) which was formally opened at the Shoreham Technical Centre in July. This state-of-the-art facility is amongst the most advanced vehicle emissions testing laboratories anywhere in the world. Already in high demand for today’s testing requirements, the facility is also future-proofed against the needs of all projected future regulatory requirements such as RDE.
Work continues to evaluate a wider range of real world driving conditions and to select the most cost effective technology as well as considering further vehicle classes and emissions legislation environments (e.g. US EPA LEVIII).
This Ricardo research project has already effectively demonstrated many of the trade-offs associated with how light-duty diesel vehicles can be developed in a manner compliant with future real driving regulations. In doing so it has demonstrated that there are some vehicle and technology combinations that show promise of complying with the expected RDE regulations.
- A Ward, T A Downes, R D Sellers, M J Campbell (2015) “Cost Effective Diesel Engine and After-treatment Technology for Future Emissions Control” JSAE Annual Congress, 2015
- May, John; Bosteels, Dirk; Favre, Cécile (2014) “A Comparison Of Light-Duty Vehicle Emissions Over Different Test Cycles And In Real Driving Conditions” FISITA 2014 F2014-CET-058
- Johnson, T., (2015) “Review of Vehicular Emissions Trends,” SAE Int. J. Engines 8(3):1152-1167 doi: 10.4271/2015-01-0993
- Pierre Bonnel (2013) “Cleaner road vehicles: How are European regulations addressing Real Driving Emissions?”
- J Seabrook, J Mullineux, “RDE and WLTC Emissions Optimisation with Co-Simulation of Real Time Physical and DoE Models”, 6th International Symposium of Development Methodology (to be presented Nov 2015)