Breath of fresh air

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Alan Warburton, head of powertrain and emissions at Horiba MIRA, discusses how RDE testing has evolved and the implications of this across the wider automotive industry

Exhaust emissions testing has been heavily researched and hotly debated in recent decades, with rising demands on efficiency and increasingly stringent emissions regulations. As ‘dieselgate’ took over news headlines this time last year, these issues were once again thrust into the limelight. While the VW scandal loomed overhead, changes to EU emissions regulations already in the pipeline began to take form.

In May this year, EU member states adopted a new level of emissions testing incorporating Real World Driving (RDE). RDE will complement revised laboratory tests to ensure that exhaust emission levels of nitrogen oxides (NOx) and particulate number (PN) are confirmed in real driving conditions.

This means cars will be tested on real roads with drivers taking the car through a variety of acceleration and deceleration patterns on different types and speeds of roads. A portable emission measuring system (PEMS), is attached to the car and will track the emissions throughout these journeys. The aim for RDE is to provide clarity between laboratory testing and emissions experienced in real-world conditions.

Once RDE is fully adopted, all car models newly approved from 2017 will have to pass on-road emissions testing, along with the lab tests, if they are to be sold. This will require significant additional investment by manufacturers and the wider supply chain, but it will add greater transparency to a vehicle’s emission output. Consumers can be more confident that the industry is delivering on reducing impact to air quality while providing ever greater vehicle selection.

While controlled laboratory analysis will still take place, testing of all vehicles must include approved RDE routes, incorporating real-world variable conditions – including urban, rural and motorway speeds, traffic, braking and acceleration control, weather (wind, rain and temperature, for example) and driver behavior. These routes, such as those at Horiba MIRA, can be used to meet regulatory requirements on behalf of certification agencies, including the UK’S VCA and the Dutch RDW.

Ten drivers could drive the same car, the same distance, with wildly different emission results due to different driving styles, weather conditions and road type – all results for output exhaust emissions are required to meet the legally defined limits. These variables are both unpredictable and unique to every use and, as such, is not something that can be currently replicated to any satisfactory standard in a lab environment.

For that reason, RDE testing also requires a different approach to traditional lab testing. Mounted to the vehicle, PEMS technology – such as the Horiba OBS-ONE series – measures the concentrations of emissions (CO, CO2, NOx, NO2), particulate matter, air-to-fuel ratio, exhaust flow rate, GPS data, environmental conditions (atmospheric temperature, humidity and pressure) and calculates mass emissions.

The advantages of the system are numerous – it is designed to be portable and adaptable and the device itself is small, lightweight and built to withstand harsh environments. Their nature lends them well to quick installation without modifications to the vehicle and an easy transference of the system between test sites. As testing can take place during the regular operation of vehicles, testing can be carried out on a number of vehicles, driving styles and conditions within a short space of time.

However, RDE testing is not without its challenges. By the very nature of its testing conditions, PEMS equipment will not deliver exactly the same result for each test. Lacking the repeatability that comes with laboratory testing, PEMS’ results have to be seen as more variable.

To buffer any ‘margins of error’ or slight variants in the data, testing guidelines include a conformity factor, defined in the regulation as a ‘not to exceed’ limit. The specification of equipment to be used for RDE testing is defined by the regulation and equipment designed by different test suppliers may deliver slightly varying results.

RDE testing will continue to develop over the next few months as results from OEM testing will inform future testing practices. From September 2017, it is expected that vehicles on the road in the UK and wider Europe will provide real-world emission levels which are helping to improve air quality.

October 26, 2016

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