Getting ‘real’ about emissions testing

09 December 2015
Getting ‘real’ about emissions testing


The following article was originally published in the
Q4/2015 issue of RQ magazine...


In an extensive and ongoing research project, Ricardo has demonstrated processes for evaluating the aftertreatment technology options for diesel cars under the forthcoming European Real Driving Emissions (RDE) regulations – rules designed to ensure on-road compliance with published type approval data for fuel economy and emissions. Anthony Smith reports.


The late summer of 2015 will very probably be remembered as the point in time at which vehicle emissions testing – in particular of diesel cars – became the subject of widespread international mainstream media, public and even political debate. The immediate impetus for this very public discourse was undoubtedly prompted by the revelation by the EPA and CARB in the United States that so-called ‘defeat device’ software had been used to circumvent regulations on some diesel cars.  

However, the resulting outpouring of concern soon began to extend further. How fundamentally effective is the vehicle type approval testing process? And why do street-level concentrations of NO2 in the urban environment remain persistently high?  

Amid widespread calls for tighter regulation, it became increasingly clear that many outside the automotive industry – and a good few within it – were largely unaware that, following many years in preparation, fundamental changes affecting the type approval testing of new vehicles were on the verge of introduction. Most importantly of all, these new regulations will for the first time create a formal linkage between testing and certification of new vehicles on the road and testing carried out in the laboratory.  

The overarching aim of this is to provide robust, reliable and directly comparable data to inform the new vehicle choices of consumers, providing a link between the laboratory and real-world driving at the same time as ensuring that future improvements in fuel economy and emissions implied by further tightening of regulatory limits also correspond to equivalent improvements where it really matters – on the public highway.

But to understand the complexity and scale of this impending change, it is perhaps useful to consider first how regulations have evolved to date.  

How did we get here?
Emissions regulation around the globe has progressed very significantly since the first rules were implemented in the 1960s in California and across the USA, with the overall goal of improving air quality and, later, reducing greenhouse gas emissions. The test cycles, emissions limits and associated requirements for diagnostics and durability have progressed in parallel with different strategies in different regions, all based on a common approach of known and repeatable lab-based vehicle testing.  

Type approval testing in Europe is carried out in the laboratory over the so called New European Drive Cycle (NEDC) in controlled conditions. Both industry and regulators have realised for some time that the process is not sufficiently well-defined to ensure that the objectives of regulation are met and have been engaged in discussions to migrate to more representative legislative approaches.  

The NEDC was defined at a time when CO2 emissions were not required to be recorded, and before fuel prices had re-escalated following the recession of the early 1990s. This was also a time when the ability to control the test environment was comparatively crude and test equipment lacked the sophistication of that available today. Moreover, it has become ever more apparent that the cycle itself is no longer sufficiently representative of the wide range of driving conditions on the roads of Europe.  

This has led to an increasing divergence between officially quoted NEDC test figures for fuel economy, and those experienced by drivers. The International Council on Clean Transportation, for example, has concluded, based on its own analysis, that the difference between official laboratory and real-world fuel consumption and CO2 was around 7 percent in 2001, but had risen over fourfold to 30 percent in 2013.


A new approach to type approval testing

The automotive industry and regulators around the world have been responding to the requirement for more representative type approval data with the development over recent years of the World Harmonized Light Vehicles Test Procedure (WLTP). In Europe and some other regions, WLTP will replace the NEDC with the World Harmonized Light Vehicle Test Cycle (WLTC), a cycle designed to be more representative of the way that vehicles are used on the road. In particular, WLTC includes a much wider load and speed range and a significantly longer duration of test.  

It is understood that there is no current plan for WLTP to be adopted in the US, though the country’s regulators have adopted several drive cycles in an attempt to cover a wider range of operating conditions. In parallel, US regulators have created mechanisms to allow consumer fuel consumption labelling to be adapted and adjusted from the base legislated test cycle results.  

WLTP also calls for the measurement of a greater range of pollutant emissions than have been mandated in previous regulations; more significantly, it will also require testing of vehicles for ‘Real Driving Emissions’ (RDE). The principle of the RDE approach will be to create a fundamental link between the rigorously controlled chassis dyno-based certification test and real-world on-road emissions control performance.  

For specific regulated emissions, limits will be set for the closely controlled laboratory-based WLTC testing, and the laboratory limit value multiplied by a maximum permitted ‘Conformity Factor’ (CF) under RDE road testing.  

Phased introduction
CF values are greater than unity for a number of reasons. The intention is to provide a limit which reflects the innate variation of real-world driving behaviour, and the ambient and topographical features of driving that can only be partially normalized by the route setting and processing tools. Moreover, measuring real-world emissions on the move is a complicated business requiring sophisticated and specialized equipment – in effect, recreating the highly sophisticated and sensitive measurement instrumentation of laboratory equipment used in the temperature-controlled and vibration-free environment of the laboratory and replicating it on the highway.  

The final specification of acceptable Portable Emissions Monitoring Systems (PEMS) equipment is currently frozen but is likely to require minor further revision before implementation. The allowable CFs have been agreed, however, by the European Commission at a meeting in Brussels on October 28; these are now to be considered by the European Parliament and Council prior to final confirmation.  

Recognizing the technical challenge of improving the real-world emissions performance of currently produced diesel cars in the short term, the Commission has agreed to a two-stage implementation, with a maximum CF of 2.1 applying for new models by September 2017, and for all new vehicles by September 2019. The second step will then follow with a CF of 1.5 by January 2020 for all new models, and applying to all new vehicles one year later in 2021.  


Some pressure groups immediately complained that this represented a capitulation to industry, somewhat spuriously claiming, for example, that it represented a 110 percent increase in allowable emissions from 2017 dropping to a 50 percent increase from 2020. This argument ignores the fact that until now, type approval limits have applied only to the laboratory test; on the public highway there was effectively no absolute limit.  

As was pointed out in the announcement of the new limits, the allowed divergence represented by the initial 2017 CF is significantly less than the current discrepancy – an average of 400 percent, according to European Commission data – found between on-highway measurements and laboratory type approval tests. On this basis, the currently proposed RDE testing process and its CFs represent a significant step forward in reducing the real-world emissions of new vehicles in Europe. The new regulatory regime will for the first time place a limit on real world emissions as well as providing a regulatory testing framework that is significantly more robust and more easily repeatable and compared than at present.  

The Ricardo RDE research project

With the advent of such a fundamental shake-up in the manner in which vehicles are tested for type approval in Europe there is clearly an imperative for an independent powertrain expert such as Ricardo to be in a position to assist its clients in developing the next generation of RDE-compliant vehicles.  

For this reason, the company has been actively engaged in a research project in parallel with the development of the new European RDE regulations. While to an extent aiming at a moving target in terms of the detail of the future test regime, this research aims to establish a development process that is capable of providing cost-effective yet RDE-compliant diesel powertrain and aftertreatment solutions. In planning the 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 RDE-compliant cycles based on routes around the company’s Shoreham Technical Centre [see box].
 

Two diesel vehicle types – a typical C-segment European hatchback and a small SUV – were the focus of the project. In addition to RDE testing, extensive use was made of Ricardo WAVE powertrain and V-SIM vehicle simulation software, using raw data generated from vehicle testing over the Ricardo RDE circuits. The engine used as the basis of the study was a 1.5 litre three-cylinder unit rated at 80 kW. For the purposes of a study based on WLTP requirements, the first task was to reduce engine-out emissions over a wider operating range than the baseline Euro 6/NEDC calibration. This was achieved through a WAVE study exploring EGR rate response at a range of operating points.  

Chemical kinetics aftertreatment models were applied to the engine-out feed-gas parameters resulting from the WAVE and V-SIM simulations for each vehicle type and for each air system and aftertreatment package. Air system options comprised high-pressure cooled EGR with a single-stage variable geometry turbocharger (VGT) and air-to-air charge air cooler, and an alternative based on high-plus-low-pressure EGR, with VGT and water-to-air charge air cooler. Aftertreatment technologies considered in the research included a lean NOx trap (LNT), and active and passive selective catalytic reduction (SCR) and SCRF, where the SCR wash-coat is applied to the diesel particulate filter (DPF) as opposed to having a separate SCR brick.

Results data processing was based on analysis using the proposed EMROAD and CLEAR data reduction algorithms intended to assess PEMS test results. While they are respectively based on very different approaches – and it is likely that just one of them will be selected for the final introduction of RDE regulations – both tools are intended to exclude abnormal outlier driving events that would skew the emitted emissions being assessed.  

Using this approach, it was possible to achieve a detailed review of the NOx control performance of the engine and aftertreatment systems of each different vehicle configuration, enabling an evaluation of the CF for each vehicle.  


Initial results demonstrate viable powertrain options
Each engine-vehicle-aftertreatment configuration was simulated over the NEDC and WLTC cycles in order to provide input to the data reduction tools, and the working assumption for the legislated NOx limit employed was 80 mg/km (Euro 6). The detailed results of this research project are to be presented at conference in mid-2016.  

“This research demonstrates that a range of technological solutions are available to achieve likely future RDE requirements,” explains Ricardo engines business unit MD Ian Penny. “However, cost-effectiveness will be crucial. For many applications, it will be challenging to meet future requirements with LNT aftertreatment alone, even when combined with wide-range NOx control.”  

As a result, the majority of diesel vehicles will feature ammonia-dosed SCR. For cars, SCRF gives the ability to place the SCR functionality in a hotter position in the exhaust, giving the potential for higher efficiencies. “For this reason it is likely in the future that the majority of diesel cars will become SCRF equipped, but for a few it may still make sense to opt for separate SCR, particularly where it is combined with other technologies such as LNT,” adds Penny.  

Ongoing research and future development
Work continues on Ricardo’s RDE research project 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 – such as US EPA LEVIII. In parallel with this, Ricardo is also running significantly more live PEMS tests for commercial customers on an RDE-compliant circuit around the Shoreham area, along with laboratory testing at the newly commissioned Vehicle Emissions Research Centre (see RQ Q3 2015).  

With the parameters of the new European RDE regulations in the process of being finalized, automakers now have a much clearer vision of the requirements they will face for the type approval of new vehicles between 2017 and 2020.  

And thanks to the preparatory research work put in place by Ricardo, automakers have two further crucial enablers. The first is a state-of-the-art combination of physical vehicle testing capability on the highway using PEMS on the RDE compliant circuit, as well as in the laboratory environment of the highly future-proofed VERC.  

The second, and no less important, asset at the automakers’ disposal is Ricardo’s RDE research: this has delivered a comprehensive end-to-end simulation capability that is able to assess different vehicle technology packages for compliance under the new RDE regulations before a commitment to hardware is made.  

As Europe moves towards implementing a more relevant type approval system for type approval with greater relevance to real-world driving, Ricardo has ensured that the toolkit is already in place to help automakers develop fully compliant models both cost-effectively and within the timescales expected of this most competitive of industries.  


This article was originally published in RQ magazine, Q4, 2015



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