What are diesel regulations and how do they work?

Euro 6 emission standards are the toughest yet. But what do they represent for petrol and diesel cars, and how are they implemented?

 

The EU has an ambitious regulatory framework in place to reduce pollutant emissions from both passenger and heavy-duty vehicles. These are referred to as the Euro emission standards.

Since 1992, successive Euro standards have set stricter limits on the amount of pollutant emissions a vehicle can emit, such as particulate matter (PM), nitrogen oxides (NOx), unburnt hydrocarbons (HC) and carbon monoxide (CO).

The results are impressive: while a diesel passenger vehicle was permitted to emit 140 milligrams of particulate matter per kilometre in 1992 this number had dropped to just 4.5 milligrams in 2014. Regulated NOx emissions have declined from 970 (combined with unburnt hydrocarbons) to 80 milligrams per kilometre over the same period.

This progressive decline in emissions is the result of a commitment by both the EU and the automotive industry to improve air quality. Technological improvements combined with legislative ambition, has led to cleaner vehicles.

The latest Euro 6 standards require diesel cars to be fitted with highly efficient NOx exhaust aftertreatment systems to reduce and control their tailpipe NOx emissions.

With the introduction of new and more robust test procedures, consumers can be confident that the diesel car they buy meets the latest tougher emissions criteria set by the EU.

By creating the Real-Driving Emissions (RDE) test, the EU became the first region in the world to introduce real world on-road testing. Under this procedure, a new car is tested on public roads and over a range of different conditions, such as low and high altitudes and speeds and uphill and downhill driving, as well as a variety of vehicle payloads and ambient temperatures.

These real-world testing boundary conditions cover more than 90% of European driving conditions and behaviours. This ensures that the test reflects real-world driving conditions rather than laboratory conditions and that vehicles deliver the low emissions required by law.

  • A car prepared for on-road emissions testing (credit: BASF Catalyst)

 

How the new test procedures better reflect real-world emissions

In September 2015, U.S. regulators revealed a large discrepancy between the pollutant emissions of a diesel car measured during the laboratory test and its emissions measured in on-road conditions. This was predominantly for nitrogen oxide (NOx) emissions.

The EU was already in the process (since 2011) of developing the RDE test procedure, which came into effect on 1 September 2017. This new, more stringent regulation measures pollutant emissions while the car is driven on the road.

Before a vehicle is released on the European market, it needs to be type-approved through a process called “homologation”. Until 2017, vehicles were only tested in a laboratory environment and checked against the maximum emissions limits set by Euro standards.

With RDE in place, cars now need to be tested with so-called Portable Emission Measuring Systems (PEMS) that provide real-time monitoring of key pollutants like NOx and particulate matter. Before a new car is granted approval for sale in the EU, the manufacturer has to commit to the maximum emissions the vehicle will produce when it is tested on the road, within the RDE boundary conditions defined in the regulation.

In addition, these on-road emission results and maximum commitment are made available to the public to aid consumers in choosing cleaner vehicles.

While a diesel passenger vehicle was permitted to emit 140 milligrams of particulate matter per kilometre in 1992, this number had dropped to just 4.5 milligrams in 2014. NOx emission limits have declined from 970 to 80 milligrams per kilometre over the same period.

The RDE test now complements the laboratory test, and therefore ensures that vehicles deliver the necessary low emissions both in the laboratory and on the road.

Laboratory tests have also been improved. Until recently, vehicles were tested according to the New European Driving Cycle (NEDC), a test that was developed in the 1980s.

Due to technological developments and evolving driving conditions, the NEDC test became outdated. To that end, UN and EU regulators have jointly developed a new test, called the Worldwide harmonised Light vehicle Test Procedure (WLTP). This was created to better reflect the on-road performance of vehicles. It was implemented in the EU on 1 September 2017.

Newly registered vehicles are now tested according to the laboratory WLTP test cycle, which complements the on-road RDE test.

 

Towards a more efficient transport future

With the introduction of new and more robust test procedures, consumers can be confident that the diesel car they buy meets the latest tougher emissions criteria set by the EU. Air quality, especially in urban environments, has become an important public health issue.

Complying with the latest RDE regulation, cars will therefore deliver the air quality benefits that citizens, local authorities and EU Member States need and depend on.

The revised framework should restore trust and transparency in the way both petrol and diesel cars are developed and sold within the European market.