Engineering news
The nitrogen oxide (NOx) emissions from diesel cars are significantly higher in real world driving conditions and on test tracks than they are in laboratory tests, a government report has revealed.
A study conducted by the Department for Transport (DfT) of 56 German and 37 UK models provided no evidence of the manipulation strategies that were used by Volkswagen to cheat emission tests, but there was a significant difference in the NOx emissions measured in the laboratory and on the road, with some cars emitting up to 12 times the EU maximum.
The news also comes after Mitsibushi’s recent admission to falsifying fuel economy tests for more than 600,000 cars, including its Nissan supplies.
The report found that emissions also varied depending on road temperatures, with engines producing more NOx in colder conditions, whereas lab tests are often conducted in temperatures of about 20°C. Manufacturers attributed this variation to exhaust gas recirculation devices, which can switch off to protect the engine in cold temperatures.
The exercise has indicated that current laboratory systems to ensure that emission limits comply with regulation are inadequate and the government has pledged to introduce new ‘real driving emissions tests’, that ‘vehicles will have to meet emissions limits in real driving conditions across a wide range of typical operating temperatures', as from 2017.
The secretary of state for transport, Patrick McLoughlin, said: “Our tests have not detected evidence of manipulation of emissions lab tests as used by the VW Group by any other car manufacturer. The tests do show the widespread use of engine management systems to prevent engine damage which can lead to higher emissions in real world temperature conditions cooler than those in the approved lab test.
“Real world tests will be introduced next year to reduce harmful emissions, improve air quality and give consumers confidence in the performance of their cars.”
The DfT has urged manufacturers to introduce new technologies to reduce emissions ahead of the new EU regulations and before the new limits are introduced.
It said: “Some manufacturers have announced that they intend to make changes to vehicles already in use, to improve emissions, and will offer this to customers on a voluntary basis. We welcome this and encourage action from other manufacturers.”
A spokesperson from Volkswagen told PE that: "We have read the findings of the government’s report on Volkswagen Group’s EU6 products and will be reviewing these test results in more detail. There were no surprises in the results of the EU6 Volkswagen Group vehicles tested which were lower than the EU5 vehicles in the report, representing the industry’s continued progress in reducing real world emissions. We welcome the move towards a test which better reflects emissions produced in real world driving conditions.
“The government report follows the publication yesterday of the new, independent EQUA Index which showed that Volkswagen Group EU6 models are among the lowest NOx-emitting on sale today. Achieving such strong ratings for our diesel vehicles during a standardised real-world test demonstrates the progress that has been made in recent years by the group, and serves to reassure consumers that they can buy our products with confidence.
“Also reassuring to customers is the evidence provided by the EQUA Index that the regulated EU6 limits were achieved by our cars not only in laboratory tests, but also in real-world driving conditions.”
A team from the mechanical engineering department at Imperial College London led the study.