The Ricardo research project is timely when viewed against the backdrop of concern over future diesel emissions and recent events at Volkswagen AG.
Despite continuing and significant reductions in the legislated light-duty diesel vehicle NOx emissions under the European Euro 1 through 5 regulations of recent years, it has been demonstrated by many researchers that real-world NOx emissions appear not to have been reduced as significantly.
This is one of the primary drivers for the proposed introduction of RDE 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 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.
Ricardo believes it is essential to establish a development process that is capable of providing cost-effective yet RDE compliant powertrain and after-treatment solutions.
In 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 after-treatment systems over a compliant RDE cycle.
This approach enabled a detailed review of the NOx control performance of the engine and after-treatment 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 says its Shoreham Technical Centre provides an “ideal 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 20km radius of the company’s technical centre.
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 after-treatment 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 Centre (VERC), 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).
As the final regulatory details and deadlines are finalized in the coming months therefore, Ricardo is thus ready to assist its clients in developing fully compliant diesel vehicles from the moment that RDE is introduced.
No doubt other R&D facilities in the UK will also be showing great interest in RDE against the Volkswagen backdrop, including no doubt the Millbrook Proving Ground in Bedfordshire which has its own on-site high-speed, urban and city driving courses as well as off-road facilities, as well as MIRA in Nuneaton.
In the light of the ongoing VW emissions saga, the measurement accuracy and repeatability of Ricardo's portable kit need to match those of Euro 6 et seq laboratory standard certification test equipment, if the results are going to be credible. That's a tall order, given the variations in ambient conditions at the roadside or even on a local roadworthiness test station rolling road.
In any case the accuracy of NOx sensor readings has always been questionable, though advances have certainly been made since the sensors first became available from NGK in Japan.
Intriguingly, NOx appears to remain the focus of attention on diesel emissions, to the evident exclusion of particulate matter (PM). But it should be recognised that engine management reprogramming to cut NOx by either increasing EGR rates or retarding injection timing will push up PM levels. If legislated PM limits are not to be breached, then upgraded DPF (diesel particulate filter) specifications will be needed, further jeopardising fuel consumption.
Post a Comment