Real and type-approved car emissions: the gap will narrow in September

Mobility · Sebastiano Salvetti · 2017-01-09

Current type-approval methods make it difficult to establish vehicles' actual pollutant emissions. The new RDE system will come into force in September of this year and will help, at least in part, to bring clarity.

The scandal known as Dieselgate began in September 2015 when the EPA, the United States Environmental Protection Agency, found that more than 500,000 vehicles belonging to the Volkswagen Group and sold in the United States were equipped with a device capable of recognising emissions control procedures, so as to temporarily alter the data and, once the tests had been passed, revert to emitting nitrogen oxides up to forty times above the permitted level. The trail that led the EPA to the German manufacturer was a study commissioned by the International Council on Clean Transportation (ICCT) — an independent American organisation dedicated to analysing transport sustainability — based on discrepancies between the type-approval tests conducted in Europe and the on-road tests carried out in America. Having lifted the lid on Pandora's box, the institute is now going further, provocatively claiming that modern Euro 6 diesel cars pollute (proportionally) more than lorries and buses.

Ciclo Nedc — The NEDC stipulates that fuel consumption and emissions measurements are taken using a rolling road, i.e. in a laboratory, rather than on the road

Wide gap between real and "laboratory" emissions

The ICCT analysis draws on a study conducted in Finland and Germany according to which, by carrying out on-road tests rather than bench tests — that is, "in a laboratory" — the average nitrogen oxide (NOx) emissions attributable to the most recent diesel-powered lorries and buses would stand at 210 milligrams per kilometre, while Euro 6-approved diesel cars would reach 500 mg/km. This latter figure, taking into account the different size and engine displacement that characterise the vehicle categories under examination, is proportionally up to ten times higher and in any case far removed from the legal limit of 80 mg/km. The warning issued by the American institute is not intended as the denunciation of a new scandal, but rather a call for the need to harmonise emissions measurement methods. While heavy vehicles are already required to undergo some on-road tests, passenger cars are still exempt.

CicloRDE-001 — Thanks to the new RDE cycle, fuel consumption and emissions will be measured by dedicated instruments under real-world operating conditions, with vehicles on the road rather than on a test bench

The NEDC cycle: measuring emissions on the bench

Thanks to EU Directive 91/441/EC, the NEDC (New European Driving Cycle) became the absolute benchmark in the automotive world, imposing a common procedure for measuring the fuel consumption and pollutant emissions of every passenger vehicle. A procedure that, in theory, was meant to replicate the typical driving conditions faced by any motorist. This aim has proved unfounded, since to date measurements have been taken using rolling roads, thus in the absence of the variables — such as tyre rolling resistance and the effect of aerodynamics — that are typical of on-road driving. During the tests, moreover, the throttle, gearbox and brakes are controlled by a computer. This anomaly is set to come to an end thanks to the new RDE (Real Driving Emission) measurement cycle.

emissioniNOx-001 — The evolution of nitrogen oxide emission limits from 2001 to the present day

Real emissions thanks to on-board devices

The RDE cycle aims to measure actual fuel consumption and pollutants during on-road driving. Currently being approved by the European Parliament, the new methodology is based on PEMS, an acronym for Portable Emission Measuring Systems: devices fitted to vehicles that allow emissions to be measured in real time. In principle, a clear step forward in the direction of transparency — were it not for the fact that, to date, no standard equipment exists for carrying out the tests. This means that the instrumentation could yield slightly different results from one manufacturer to another. In addition, since the tests will take place on public roads alternating between urban, extra-urban and motorway stretches, the influence of weather conditions could prove far from negligible, making it necessary to repeat measurements several times throughout the year. Unless this degree of approximation is eliminated, there is a risk that the RDE cycle will serve as a supplement to the NEDC system rather than a full alternative, pending the universal WLTP standard (Worldwide harmonized Light vehicles Test Procedure), which is still far from being defined.

Emissioni delle auto reali e omologate, a settembre si ridurrà il divario

Measurements under the NEDC cycle are conducted on a rolling road, at a constant temperature of 25 degrees, with airflow assisted by a fan, near-empty fuel tanks, accessories switched off, equipment reduced to a minimum and a 75 kg ballast to replicate the presence of the driver

No human being is able to replicate the results obtained in the laboratory. The NEDC cycle therefore has a comparative value between vehicles, but cannot be taken as a true indicator of a car's real-world consumption

The RDE cycle, more accurate than the NEDC system as it is based on measuring emissions under real-world driving conditions, will come into force from September 2017

A pioneer of the RDE cycle, PSA Group – which controls the Peugeot, Citroën and DS brands – will adopt the new procedure for measuring nitrogen oxide emissions during the course of 2017

The advantage of measurements conducted in the laboratory lies in the repeatability of tests under constant conditions. Unfortunately, however, this testing methodology is too far removed from reality

The NEDC cycle is also applied to electric cars. This is why the range declared by manufacturers often proves to be far from reality

Unlike cars, lorries and buses are subject to a series of type-approval regulations that already include on-road testing

Alongside carbon dioxide, nitrogen oxide emissions are among the most dangerous to health

The transparent revolution in emissions

The introduction of the RDE system in Europe – where it is not planned in the United States – will take place in two phases: manufacturers will first have to reduce the gap between "laboratory" emissions and real-world emissions by meeting a conformity factor of 2.1 (that is, with a tolerance of 110 per cent) by September 2017 for new models and no later than September 2019 for newly designed cars. In a second phase, this gap will be brought down for all vehicles to a factor of 1.5 (meaning a tolerance of 50 per cent) by January 2021. This objective is all the more significant when one considers that recent studies conducted by the Canadian Ministry of Health on a sample of 6.6 million people have shown a direct correlation between exposure to high levels of smog and the progression of neurodegenerative diseases, most notably Alzheimer's disease. A (transparent) revolution is more necessary than ever.