The latest analysis of the EQUA Index data shows that the average daily distance driven in passenger cars is not sufficient for a vehicle’s pollution control system to warm up and become fully functional. The resultant high levels of cold start NOx emissions, from both gasoline and diesel engines, could provide an additional challenge for urban air quality initiatives such as the proposed Clean Air Zones in the UK.
According to the Department for Transport more than half of car driver trips nationally are under 5 miles. In Inner London, the average journey distance by car per-person-per-day is just 1.5 miles. For the majority of vehicles tested by Emissions Analytics, it can take more than five minutes for after-treatment systems to reach operating temperature.
The table below shows the uplift in NOx for cold starts tested at 1 minute and 5 minutes from key-on, compared to when fully warm, across the combined EQUA Index cycle.
|Absolute NOx emissions
|Ratio to official limit
|Uplift on warm||Absolute NOx emissions
|Ratio to official limit
|Uplift on warm|
Gasoline has lower NOx in absolute terms but proportionally has much higher NOx in the first minute, but which then falls more rapidly than for diesel cars. This is typically as the three-way catalyst reaches effective operating temperature.
More generally, the thermal management of exhaust systems for engines where the exhaust frequently cools, such as with stop-start technology or hybridisation, is of growing importance in limiting NOx emissions.
By looking at the average NOx emissions of 5% of the data with lowest instantaneous exhaust temperatures from each Euro 5 and 6 passenger car test (excluding data points where the engine is off), and comparing it to the average NOx emissions when the engine is warm, it shows a very similar picture to the cold start data.
|Absolute NOx emissions
|Absolute NOx emissions
|Lowest 5% exhaust temperature||0.719||0.098|
Gasoline engines suffer proportionally much more from cooler exhausts although produce less NOx in absolute terms, whereas the diesel engines have a 29% uplift in NOx when the exhaust temperature is lower. In terms of total emissions, the average uplift is 0.160g/km for diesels and 0.067g/km for gasoline vehicles.
The potential introduction of Clean Air Zones in UK cities is a cornerstone of the government’s strategy to reduce air pollution. However, driver behaviour in cities (short trips, the use of stop-start technology and/or choice of hybrid vehicles), when combined with exhaust after-treatment technologies which are sensitive to exhaust temperature, means that other measures will be necessary if NOx emissions are to be reduced.
Encouragingly, the EU has acknowledged the importance of cold start emissions by including their measurement in the new Real Driving Emissions regulations that start in September 2017. However, there is a danger that the effects are under-measured compared to real-world journeys of short length.
Vans weigh in on the EQUA Index
Light commercial vehicles (LCVs) travelled 48.5 billion miles last year according to the Department for Transport. In its tests, Emissions Analytics has seen similar levels of variability from official fuel economy and emissions figures in vans as in cars. With van mileage growing by an average of 4.1% each year this is bad news for air quality and for van driver’s wallets. Launched today, drivers can now use the EQUA Index to check the on-road performance of light commercial vehicles.
The table below shows a sample of the vans tested. All give fewer miles per gallon than advertised. The average is 17.1% below but the range is from -5.3% to -38.8%. However, the mpg gap is smaller than for passenger cars which was 29% in 2016, perhaps because light commercial vehicles are not being hyper-optimised to the NEDC.
Similarly, all of these vehicles were homologated to either the Euro 5 or Euro 6 standard and yet there are seven Euro 5s and three Euro 6 vehicles which have been rated ‘H’ on the EQUA Aq Index, meaning they emit 12 times or more the current Euro 6 limit when they are out of laboratory conditions.
The best performing diesel van is the Euro 6 VW Transporter, scoring an B-rating on-the-road, meaning it is just 1.5 times the legal limit. This is mirrored in the passenger cars tested, where only 15 of the 131 Euro 6 diesel cars tested meet the standard, of which 10 are from the Volkswagen group.
|Make||Model||Regulatory stage||Variance to official MPG||EQUA Aq rating|
|FORD||Transit Connect||Euro 5||-16.7%||E|
|FORD||Transit Custom||Euro 5||-22.7%||H|
|FORD||Transit Custom||Euro 6||-16.1%||C|
The effect of load
Tested on the same EQUA cycle as passenger cars, vans additionally run parts of the route ballasted to fifty per cent of their maximum payload. The effect of load on fuel economy is an average of -11.2% for a fully loaded van. A quick calculation based on average diesel price (122.12p/l) shows that for every 100 miles driven with a fully loaded van, refuelling costs on average £1.91 more than empty. Multiply this by the average yearly mileage travelled per van  and this is approximately £450 per year.
With around 30 to 50 vans added yearly, the EQUA Index is available for everyone to use free of charge and enables drivers and fleets to pick the most economical as well as the least polluting vehicles. Find out more by looking at the EQUA Index online.
This year’s round up of EQUA fuel economy data shows a five percentage point increase in the gap between official and real-world mpg, reaching 29% in 2016.
Official mpg figures averaged 60.7mpg in the year, the highest we have seen since we started recording in 2011. This is an increase of 9% on 2015’s figures, which stood at 55.7mpg; however, real-world mpg reached just 42.3mpg. On a like-for-like basis, this represents a 3% increase on 2015.
With air conditioning now widely available in cars, in 2016 Emissions Analytics updated all its mpg results to include the effect of air conditioning on fuel economy. Results are now expressed to reflect manually adjusted air conditioning (not automatic climate control) switched on at 50% of maximum throughout the test. This increases fuel consumption typically by 4%.
Incorporating the use of air conditioning, the gap between official mpg figures and real-world EQUA Index Mpg has risen to 29% on average, with the largest gaps well exceeding 40%. This increases to 75% below the official figures for hybrid vehicles that have not had their battery charged and are running purely on the ICE.
Can regulatory change reduce the gap?
From 1 September this year the World harmonised Light duty vehicle Test Procedure (WLTP) will be introduced to certify the carbon dioxide and fuel economy of cars. Work started on this around 2008 and was originally intended to be a worldwide certification standard. However, with the passing of significant time and the withdrawal of North America from the process, it has become less relevant.
It will still be an improvement on the existing type approval process, which incorporates the New European Driving Cycle (NEDC), largely due to the removal or restriction of loopholes in the procedure. However, the test cycle itself is not much more representative of real-world driving, as it remains in the laboratory with no changes in elevation and still modest acceleration rates. Our prediction, also consistent with modelling from the International Council on Clean Transportation, is that the current mpg gap of 29% and the CO2 gap between official and real-world of around 40% will approximately halve. So, a significant gap will still remain.
Crucially, it has yet to be agreed when and in what way the WLTP results will be made available to consumers. In the meantime the EQUA Index is available for anyone wishing to find out the on-road fuel economy of both Euro 5 and Euro 6 vehicles.
Hybrids have always had a miles-per-gallon advantage in urban driving but new EQUA Index data shows that they are gaining on diesels in motoway or highway driving and, if current trends persist, hybrid electric vehicles (excluding plug-in hybrid electric vehicles) are set to take the lead in 2017.
The dotted trend lines in the above graph, representing motorway mpg for diesel vehicles and gasoline hybrids tested by Emissions Analytics, are converging. While the downturn in diesel mpg may be due to a change in manufacturers’ focus from fuel economy to NOx emissions, what is more striking is the improvement in gasoline hybrid performance on the motorway as a result of technological advances.
The step change in technology is even more noticeable when European EQUA data is compared to North American EQUA results. The graph below shows gasoline hybrid performance in the US is particularly impressive on our combined cycles. With this level of fuel economy it seems unlikely that diesel vehicles will ever make a significant impact on market share in the US. With the mpg penalty of some NOx aftertreatment systems, perhaps it was to gain a fuel advantage over hybrids that Volkswagen resorted to using a defeat device when bringing their diesel models to the US market.
Another noticeable effect of the different product mix in the US is the level of carbon monoxide emissions. Both regular gasoline cars and gasoline hybrids have much lower CO emissions than their European equivalents, with regular gasolines 30% lower and gasoline hybrids 64% lower. This is despite the fact that the US have a less strict limit, at 2.1g/km, than the EU’s, 1.0g/km limit.
When we last wrote about hybrid vehicles back in October 2014, we concluded they were delivering “good but not best-in-class fuel economy, but [were] typically the cleanest, and if you are a light-footed, congested town driver, they are ideal.” Two years on hybrids, particularly in the US, have really upped their game. They are still a cleaner drive than a diesel and may soon offer better fuel economy wherever you drive them but heavy-footed drivers should still exercise caution.
As the government loses a second high court ruling brought by ClientEarth, many are now sounding the death knell for diesel cars. Not so fast, says Emissions Analytics, diesels can be clean and govenments are highly unlikely to give up the greenhouse gas advantage of diesel in the short- or medium-term.
Since the introduction of Euro 6 in September 2014, manufacturers have been forced to improve their after-treatment systems to meet the stricter legislated limits for NOx. Exhaust Gas Recirculation, Lean NOx Traps, and Selective Catalytic Reduction technologies have been employed as part of a complex strategy to reduce tailpipe emissions. There have been variable successes, with some achieving the regulated limits even in real-world driving and the worst more than 20 times the legal limit. Overall, average NOx emissions from Euro 6 diesels are down 55% compared to Euro 5s.
Nonetheless, there is still the fact that many new cars do not meet the legislated limits in real-world operation. Our data shows NOx emissions are on average 4.3 times over the limit for Euro 6 cars and, after a period of improvement, this Conformity Factor is rising. This is the heart of the issue, as to whether diesels are the major and unavoidable cause of poor air quality in towns and cities.
Consequently, there have been many suggestions made to combat the problem of dirty diesels. These range from the London Mayor’s T-charge, to a diesel scrappage scheme, to a total ban on diesel vehicles in certain zones. However, Emissions Analytics’ data shows that modern diesels in their own right can be clean.
Since the launch of the EQUA Air Quality Index six months ago, twelve cars have how achieved an A-rating including the latest Volkswagen Tiguan, meaning it has met the 0.08g/km limit in real-world driving.
There is also the issue of CO2 emissions to be considered. Despite Donald Trump tweeting that climate change was, “created by and for the Chinese in order to make U.S. manufacturing non-competitive,” the British government has an empirical view on global warming and stands by its commitment to cutting its carbon footprint. Would ministers give away the 16% CO2advantage – according to Emissions Analytics’ testing – diesel has over gasoline for the same distance driven in real-world operation, until there is a viable alternative.
In the future electric and hybrid vehicles may deliver the CO2 advantage required, as well as greatly reducing, or eliminating, NOx and other harmful emissions, at which point diesel powered engines for passenger cars may come to the end of the road. However, with a share of the market of less than 2%, there is still a way to go for these vehicles. Until then, Emissions Analytics’ data strongly suggests the policy focus should be on sorting the clean from the dirty diesels and incentivising manufacturers to bring forward clean technology.
The latest EQUA Aq Index results are available online
Emissions Analytics is pleased to announce the launch of the EQUA CO Index. The second in the EQUA Index series, EQUA CO looks at whether carbon monoxide regulations are being achieved in real-world operation.
Potentially fatal for humans as well as damaging to the environment, carbon monoxide is generally considered a problem primarily confined to gasoline vehicles. Regulations distinguish between the fuel types, with diesels having a more stringent but, due to their technology, easier to achieve limit of 0.5g/km. Gasoline vehicles have to meet a more generous 1.0g/km limit which is typically achieved using a three-way catalyst. Therefore, the regulations are not technology neutral and allow gasoline vehicles to emit twice that of diesels and still be compliant.
In the same way that Emissions Analytics rates emissions of NOx from diesels, gasolines and hybrids with a single scale on the EQUA Aq Index, the EQUA CO Index awards a universal rating regardless of fuel type. Thus despite the regulations setting different boundaries, the EQUA CO Index allows comparisons between vehicles. The A++ to H ratings are set as follows:
Using these classes, a diesel car awarded an A to A++ meets the regulated level even in real-world driving, whereas a gasoline vehicle with a C to A++ meets the regulated levels for this fuel.
Of the 734 vehicles currently on the EQUA CO Index, 96% emit the regulated amount of CO or less. However, there are some interesting exceptions. Several Mercedes C-Class diesels are over 0.5g/km, out of a small number over the limit. Additionally, 8% of gasoline vehicles, that is 24 models tested by Emissions Analytics, do not meet the regulated limit, with one outlier being more than six times over. If the regulations were to change and gasolines had to achieve the same, stricter standard as diesels, the number of cars failing to reach this standard would increase to 20%. Of the hybrid vehicles tested, all achieve the regulated limit apart from the Mitsubishi Outlander which scored a D-rating when not running on its electric engine.
The vehicles tested by Emissions Analytics are all run on our standard real-world cycle. The tests are conducted by a small pool of highly trained technicians and the vehicle and testing equipment is carefully prepared to make sure it is fully warmed up and in the manufacturers’ default settings.
The data shows that illegal levels of carbon monoxide are not as prevalent in real-world driving as excess NOx from diesels. However, given the toxicity of CO, this is a situation that needs to be monitored. This could become particularly relevant if there is a market shift away from diesel towards gasoline as a result of dieselgate and other emerging regulations and taxes. Emissions Analytics will continue to keep a watchful eye on on-road vehicle performance, checking it against official certification and publishing the results online on the Carbon Monoxide page at the EQUA Index site.
Subscriptions are available to the Emissions Analytics database. Contact us for details.
Recent months have seen a growing a body of evidence, from different sources, that NOx emissions from cars are higher when the ambient temperature is lower. This month, Emissions Analytics mined its real-world database to assess the evidence.
The accusation is that NOx reduction devices, including exhaust-gas recirculation, are programmed for reduced operation below the 20°C of the official test. The effect would be higher NOx emissions, with the motivation supposedly to deliver better real-world fuel economy.
Some manufacturers argue that this is, in fact, to protect the engine from damage at lower temperatures, and that doing this is perfectly legal. However, with average temperatures in the UK around 9°C across the year, this has a potentially significant impact on air quality and governments’ attempts to achieve air quality targets.
To quantify the issue, we segmented NOx data from our on-road PEMS tests into groups above and below 18°C, and found the following differences in the average Conformity Factor (ratio of real-world NOx to official limit).
Conformity Factors of Euro 5 & 6 vehicles above and below 18°C
While the result for the Euro 5 vehicles was statistically significant, this was not the case for Euro 6 due to a small number of very high emitters. As our sample size increases, we will be better able to assess whether there is a pattern for Euro 6 cars.
Looking in more detail at the Euro 5 vehicles, the data suggests that there are seven manufacturers with clearly higher emissions below 18°C, which is shown in the chart below.
Conformity Factors for Euro 5 vehicles by manufacturer
The intention of this newsletter is not to name names, but to indicate that it is not one manufacturer but several that may be utilising the thermal window loophole. If the hypothesis is correct, it could mean that many millions of vehicles on the road today in UK and the colder parts of Europe are putting out higher emissions than expected. Further, as Euro 5s, these vehicles are not that old and therefore will be on the road for many years to come.
With Mitsubishi Motors the latest manufacturer to admit to impropriety in its testing procedures, the need for impartial real-world data has never been greater. Today Emissions Analytics is launching the new EQUA Index rating scheme to help bring transparency in the first instance to the issue of air quality.
The EQUA Air Quality Index is based on the level of emissions of nitrogen oxides (NOx) in grams per kilometre emitted during our real-world tests. The Index aligns the boundaries between ratings values as much as possible with recognisable points. See below:
The EQUA Air Quality Index is intended to complement the forthcoming regulations for new vehicle certification, by monitoring vehicle performance when driven normally on roads; in effect keeping a watchful eye on the effectiveness of the new regulations.The problems with the existing test system, the NEDC, which have been the cause of so many of the issues covered by the media recently, are already being addressed by regulators in Europe. From 2017 the World Harmonised Light Duty Test Protocol (WLTP) will change the way CO2 is measured and Real Driving Emissions will address problems with NOx measurement.
The other great benefit of the EQUA Air Quality Index is to help car buyers. Designed to be clear and concise, the simple A to H rating allows manufacturers and retailers to show how different models compare in the showroom, whether diesel, petrol or hybrid. It is also ideal for car reviewers and publishers to include as new cars are reviewed. And because the scheme is independently financed and researched, consumers, companies and the wider automotive industry can have confidence in the impartiality of the data.
The EQUA Air Quality Index has been developed by Emissions Analytics in conjunction with a group of experts to guide, review the test and rating methodology, monitor the regulatory context, and provide input into the wider development of the index. The group includes:
- Professor Helen ApSimon – Air Pollution Studies, Imperial College London, UK
- Dr Adam Boies – Department of Engineering, The University of Cambridge, UK
- John German – Senior Fellow, The International Council on Clean Transportation, USA
- Dr Marc Stettler – Centre for Transport Studies, Imperial College London, UK
- Professor Martin Williams – Air Quality Scientist, King’s College London, UK
There are almost 450 vehicles on the EQUA Air Quality Index now, so why not have a look?