Error parsing XSLT file: \xslt\FacebookOpenGraph.xslt New tests reveal extent of misleading NOx figures
Cookies on Businesscar

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive all cookies on the Business Car website. However, if you would like to, you can change your cookies at any time

BusinessCar magazine website email Awards mobile

The start point for the best source of fleet information

New tests reveal extent of misleading NOx figures

Date: 12 July 2016   |   Author: Debbie Wood

Tests that replicate real-world driving by data analysis firm Emission Analytics have revealed that Euro6 diesel engines are up to 14 times dirtier on NOx emissions than their official figures suggest.

Of the 100 Euro6 cars tested so far by the company, models from Vauxhall, Fiat and Ssangyong have been highlighted as the worst-polluting, while Euro6 diesels from the VW Group scored the best ratings.

There are eight grades. An A-C rating means the car meets current Euro6 emission standards in replicated real-world driving, while G-graded cars emits more than 10 times the limit and H-graded vehicles pollute at least 12 times over Euro6 thresholds.

"Of those we've tested and that are on sale today, seven have 'A' ratings and every single one is from the VW group. Their new engines are among the cleanest in the market," Emissions Analytics CEO, Nick Molden told BusinessCar.

Emissions Analytics is able to test up to 400 cars a year in the UK and conducts its tests on a fixed road route with all cars conditioned in the same way beforehand - for example, the engine is warmed up and all the windows are closed. Data analysis is used to add traffic variables and all cars are driven by trained technicians, while parts of the same road are also re-tested but deliberately driven more aggressively and gently to see what the variations are.

One of the key reasons cars fail to match official NOx figures in actual real-world conditions is that after-treatment systems, such as Adblue, fitted to most new diesel cars can actually turn themselves off if the outside temperature falls below 18°C due to a provision in the regulations aimed to protect the engine from condensation; however, Molden believes manufacturers programme these systems to turn off at temperatures that they choose to improve mpg performance.

They are, however, working at their optimum during official New European Driving Cycle (NEDC) type-approval tests, which are carried out in a controlled lab set at 20°C.

"I think there's good engineering reasoning why these systems may be turned off [by manufacturers] at -10°C, but not at 15°C. Because [the regulation] is  worded in such a vague way, there's been exploitation of this," said Molden.

According to Molden, stop/start is another example of a system that works well for official tests, but in real-world driving doesn't deliver the same results.

"Stop/start is one of the great examples of something which would not exist if it wasn't for the deficient NEDC current regulations. You get a big benefit from the type-approval test but, in real-world driving the technology kicks in less often and gives a much smaller benefit."

Official tests for car emissions and fuel economy are due to be replaced soon and there are plans to incorporate real-world driving into the new test in 2017.

The best and worst Euro6 engines

A-graded diesels
Audi A5 2.0 161 manual
Seat Alhambra 2.0 150 manual
Skoda Superb 2.0 148 manual
VW Golf SV 2.0 148 Auto
VW Passat 1.6 118 manual
VW Scirocco 2.0 148 manual
VW Touran 1.6 108 manual
G-graded diesels
Infiniti Q30 1.5 108 manual
Subaru Forester 2.0 145 auto
Vauxhall Zafira Tourer 1.6 134 manual
H-graded diesels
Fiat 500 X 1.6 118 manual
Porsche Panamera 3.0 300 Auto
Ssangyong Korando 2.2 176 manual