Part of the fall-out from the Volkswagen diesel emissions scandal has been the shining of a spotlight on the inadequacies of existing emissions testing procedures.
The New European Driving Cycle (NEDC), which is supposed to represent the typical usage of a car in Europe, has come in for particular criticism for not replicating real-world driving conditions, and having numerous loopholes that mean the test figures are unachievable in practice.
The NEDC has the word ‘new’ in its title, but it was introduced in the 1970s and last updated in 1997. It has been described by some industry experts as being unfit for purpose, and there have been calls for it to be replaced with greater urgency – the current schedule is for after 2017 – by the World Harmonised Light Vehicle Test Procedures (WLTP), and specifically the World Harmonised Light Vehicle Test Cycle (WLTC), a testing regime that has been designed to be more representative of the way that vehicles are used on the roads.
The main complaint about the NEDC has been its inability to represent real-life driving, having been conceived at a time when vehicles were lighter and less powerful. It offers a stylised driving speed pattern with low accelerations, constant speed cruises, and many idling events. However the transient accelerations are much steeper and more dynamic in practice, in part caused by the power surplus of modern engines. Furthermore, under the NEDC, cycles can be performed using optional economy settings that will not typically be selected by drivers. The test cycle, for instance, is performed with equipment such as air-conditioning and heated windows switched off; the tests can be carried out at 1.2mph (1.9km/h) below the required speed, so using less fuel; roof rails and passenger door mirrors can be removed for the test; and tyre pressures can be set above the recommended values, reducing rolling resistance.
The perceived shortcomings of the NEDC were sharply criticised in a damning report by the Brussels-based Transport and Environment (T&E) campaign group, which said that the gap between test results and real-world performance has become a “chasm”, increasing from 8% in 2001 to 31% in 2012 and 40% in 2014. Without action, this gap will grow to almost 50% by 2020, it said.
Mercedes cars have the biggest average gap between test and real-world performance, says the report, with real-world fuel consumption exceeding test results by nearly half. None of the improvements in emissions measured in tests of Opel/Vauxhall cars since 2008 has delivered improvements on the road, says the T&E, with the real-world fuel economy of its cars actually getting worse. Of the apparent improvement in emissions from the launch of the Mark 7 VW Golf (Europe’s best-selling car), just one-fifth has been achieved on the road.
The T&E report concludes by stating that the system of testing cars to measure fuel economy and CO2 has been “utterly discredited”. It calls for the introduction of the WLTP by 2017, and the establishment of a European type approval authority to better ensure that tests are performed consistently and independently. These changes would, in the T&E’s opinion, align the EU testing system with that in the US, which is deemed far more effective in identifying and addressing abuses.
Unfit for purpose
Philippa Oldham, head of transport and manufacturing at the IMechE, says that the industry had known for a long time that the NEDC was not fit for purpose, but that there seemed to be a tacit acceptance of its failings.
“To many working within the automotive sector, the VW story did not come as a surprise,” she says. “In 2012, What Car? magazine took action with the launch of the True MPG campaign, which pointed out the discrepancy between laboratory testing conditions under the NEDC and real-world emissions. Many agree that the current method for testing car emissions is out of date, and the UK is seeking agreement from the European Commission for a new emission test which embraces testing technologies that are more representative of on-road conditions.
“In 2017, we anticipate the introduction of the WLTP and, specifically, the WLTC. This is intended to give a more ‘real world’ scenario, but many believe this still does not go far enough. Alongside this, Real Driving Emissions (RDE) criteria are being developed, which, it is hoped, will be fully integrated by 2025 and should give us a true picture.”
Meanwhile, Tim Barlow, principal consultant at the Transport Research Laboratory, is also critical of NEDC. “What the VW emissions scandal has done is to bring to the forefront the need for changes to existing test procedures. Current testing methods are outdated and offer room for error or optimisation, so it’s imperative that industry, governments and regulatory bodies work together to find the best way forward,” he says.
“Ideally, we need to move towards a testing model that’s based on real driving emissions, carried out with vehicles operated on normal roads. This should be followed up with in-use compliance testing, whereby a sample of vehicles already in use are tested to check they still comply with the emissions limits.”
For the time being, the answer comes in the form of WLTP, defined as a global harmonised standard for determining the levels of pollutants and carbon dioxide emissions, fuel or energy consumption, and electric range from light-duty vehicles (passenger cars and light commercial vans). The test procedure provides strict guidance regarding conditions of dynamometer tests and road load (motion resistance), gear shifting, total car weight (by including optional equipment, cargo and passengers), fuel quality, ambient temperature, and tyre selection and pressure.
Three different WLTC test cycles are applied, depending on vehicle class defined by power-weight ratio, PWr, in kW/tonne. In each class, there are several driving tests designed to represent real-world vehicle operation on urban and extra-urban roads and motorways.
The WLTP represents two fundamental changes in the way that vehicles are tested. It has been designed to be more representative of the way that vehicles are used on the roads, including a much wider load and speed range and a significantly longer duration of test. It also calls for the measurement of a greater range of emissions than have previously been specified.
Search for precision
According to Jon Andersson, manager of aftertreatment and chemical analyses at engineering consultancy Ricardo, the WLTC represents a step forward. “It will firm up many of the specific testing requirements and specifications in comparison with those of the previous NEDC approach – for example, in defining more precisely the means by which coast-down data is obtained and the temperature at which laboratory testing must be carried out,” he says.
“Conversely, some aspects that were considered over-prescribed in the NEDC, such as the shift points for manual transmission powertrains, have been relaxed, so that testing can be made more representative of the manner in which the vehicle will be used on the road.
“Real Driving Emissions (RDE) will form part of the WLTP, to run alongside laboratory-based testing. The aim of this change is to bring into the test procedure an element intended to be representative of ‘normal European driving’. The final specification of RDE testing, and the compliance requirements of acceptable portable emissions monitoring system (PEMS) equipment, are frozen, but are likely to require further revision before implementation. Our current view is that RDE will be based on approximately equal lengths of urban, rural and motorway of at least 16km respectively, and subject to specified upper and lower averaged speeds, providing an individual test duration of 90-120 minutes.”
A significant volume of data will be generated in RDE testing, for which standardised data reduction algorithms and procedures are being finalised. For each of the regulated emissions covered by RDE, the total emissions recorded via PEMS testing will be compared to the regulatory limit for the same vehicle, to arrive at a Conformity Factor (CF). While many technical details, and the precise timing and sequencing of introduction, remain to be defined, the principle of the RDE approach will be that, for any regulated emission, limits will be set both in terms of that allowable in the laboratory under WLTC testing, and the same value multiplied by the maximum permitted CF under RDE road testing.
“Because of the specific definitions of RDE, which is the consequence of the selected boundary conditions, it’s demanding to generate a suitable route for testing vehicles, and of course no two routes or two sets of traffic conditions can ever be completely identical,” says Andersson.
“The RDE approach is thus qualitatively different from the laboratory-based cycle, which is carried out under precisely controlled and highly repeatable conditions. Instead, PEMS-based RDE testing will create the link between laboratory-based chassis dyno testing on the new WLTC and real-world driving, with a similar mix of dynamic activity. It also provides a bridge to the assessment of emissions under other types of real-world driving, and as a research tool will enable greater understanding of driving style influences, climatic effects, and many other areas that were until recently hard to access for the engineer.”
Ricardo is preparing for the development of compliant vehicles under future RDE regulations. As with existing vehicles, development effort in the future is likely to fall into the areas of base engine and combustion system technology, calibration and aftertreatment design. These efforts will be required across all powertrain types involving the use of combustion engines, including advanced ‘intelligent electrification’ approaches, plug-in hybrid electric vehicles and alternative fuelled engines.
Andersson says: “The important aspect for Ricardo, in ensuring that the company is prepared for the requirements of RDE, was to carry out this research even before the final details of the testing procedure have been fully defined. In this way, our customers can have confidence that we’ve invested effort in understanding the practicalities of implementing the new testing procedure as a part of the new vehicle development process, and we can be ready to adapt to the final regulation as soon as this is confirmed.”
So the industry thinks that the over-arching WLTP and the WLTC testing procedures will deliver significant improvements over NEDC for the testing of light-duty vehicles. But that’s not, perhaps, the end of the story. As automotive technologies change, so the testing procedures that the industry puts in place should evolve.
Oldham at the IMechE thinks the industry cannot afford to stand still when it comes to emissions testing. She says that, in the light of the VW scandal, the UK government has declared its desire to re-examine the automotive emission testing carried out in the UK. “If this re-examining is occurring, perhaps they should take stock and see if more can be done in terms of future-proofing this test? What about looking at the lifecycle emissions? If we are looking towards a future that has a large percentage of the fleet made up of plug-in hybrids and electric vehicles, should electricity-generation emissions be considered?”
Looking at the wider perspective, there needs to be a better understanding of the sustainability of the emissions coming from our transport fleet, says Oldham. This is the direct relationship between CO2 emissions, fuel type (including electricity) and fuel consumption, the technical compromises between increasing engine fuel efficiency, particulate production and NOx generation.
Whatever happens, she thinks diesel should remain a key part of the fuel mix if the UK is to meet its CO2 reduction goals, as diesels are accepted as being better at reducing CO2 than petrol cars. “If we took all diesel cars out of our fleet, the average CO2 emissions calculation of the fleet would go up by 16g/km,” she says.
Since April, Oldham has been the chair of a Coalition of Advanced Diesel Technology – a consortium made up of key members of industry from tier-one automotive suppliers and experts from academia. One of the key messages that is coming out of its work, she says, is that diesel technology has been developed by engineers to help improve air quality by reducing emissions.
“The technologies to reduce emissions are available: these include solutions such as engine optimisation (through turbocharging and fuel injection), oxides of nitrogen reduction through active NOx storage catalysts and selective catalytic reduction, as well as particulate matter filtration systems (in the form of closed filters that have a typical particulate filtration efficiency of greater than 95%),” she says.
“With all the negativity surrounding diesel vehicles, this important message is being lost. Globally, we need to meet our emission targets. To do this, we need to find an approach to decide how we phase out old vehicle types, based on real-world emissions and not fuel type, to help significantly improve air quality. We need a robust policy framework to ensure that these targets are delivered.”