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Emissions Analysis: Downsizing 'fad' no longer relevant

Date: 22 July 2016   |   Author: Debbie Wood

Choosing smaller, downsized diesel engines has, for many years now, been seen as a textbook way to reduce fleet emissions, improve fuel economy and lower BIK tax bills for company car drivers.

However, results from Emissions Analytics show that smaller engines actually perform worse for NOx and fuel efficiency when driven in real-world conditions, and Nick Molden, the testing firm's CEO, believes it's time for the downsizing 'fad' to come to an end.

"For Euro6 [emissions standard] we've found that the very small engines have worse fuel economy than the bigger engines. It collides with the downsizing fad, which we've always considered a complete error," he tells BusinessCar.

Emissions Analytics has been testing cars in typical real-world conditions for a number of years now and conducts them independently from the standardised tests. Up to 400 cars a year are tested by the firm here in the UK, and there are plans to expand further over the next 12 months.

According to Molden, it's the 2.0-litre diesel that proves the sweet spot for fuel economy and emissions, especially if drivers are covering a lot of miles each year.

"For mixed use, the 2.0-litre diesel is the sweet spot. Some 1.6-litre and 1.4-litre engines are so woefully under-powered that you have to work the engine a lot harder, resulting in worse fuel economy, higher CO2 and, if it were a downsized diesel engine, a NOx problem too," says Molden.

The results suggest that although on paper a lower-powered 1.6-litre diesel brings greater fuel economy, choosing a larger engine if drivers predominantly travel on the motorway and have a harsher driving style will be a more cost-effective choice, and Molden believes fleets need more advice when compiling choice lists.

"All the norms of downsizing have gone out of the window with Euro6, but everyone is still thinking about the rules of thumb that we've all been historically taught to believe," he says. Prior to Euro6 regulations, this wasn't the case, but the technology required to meet the latest standards has led to the current situation.

The testing firm publishes results on its website and is encouraging fleets to use the data as a benchmark to compare cars against each other.

"We want fleets, when they are defining their choice list of cars, to start using our tool to make more informed choices. This is a tangible way fleets could make a difference and it doesn't mean cutting out all of the big cars; far from it - if you select right you can put big-engined, high-performance cars on the list too."

Driving style can have a significant impact on running costs, and the fuel economy numbers published are the averages achieved during the firms real-world testing process. However, the company is considering launching a tool that will allow fleets to customise for driving style to help drivers choose a car that will deliver the best fuel economy results.

"If you're an aggressive driver who constantly travels on the motorway and uses the air-conditioning a lot, our system will configure a more indicative figure of what you could realistically achieve on the road," says Molden.

Recent real-world economy results of new Euro6 engines have revealed that adopting a more aggressive driving style has varying effects on fuel economy depending on engine size, with the larger 2.0-litre diesel engines proving just as economical regardless of how harshly they are driven.

"What we have found is that in some cars, the bigger engines perform the same whether they are driven aggressively or not. It's the cars with downsized engines which see big variations in results and stray the furthest from official figures," concludes Molden.

What about CO2?

The current data available on the Emissions Analytics website focuses on NOx emissions - critical to local air pollution problems - which brings with it damning ratings for a lot of diesel engines.

Results from real-world tests for CO2 emissions will be available in the near future, though, which will put petrol engines back in the spotlight.

The average petrol is about 40% below the Euro6 limit (around 50mg) for NOx, verses 400mg for diesel; however, petrol engines generally emit more CO2 and Emissions Analytics' Nick Morden doesn't want fleets to forget this fact.

"What we don't want is people moving from diesels to petrol, as although NOx will reduce, CO2 will increase as a result," he says.

According to Molden, there's still a great deal of confusion with fleets around what NOx and CO2 emissions are and how they differ, and he is urging fleets to take a more holistic view when selecting cars for the choice list, opting for vehicles that are fit for purpose rather than seemingly low-emitting.

"What we're trying to do is advise consumers who are buying or choosing a car today. You need proper robust data so people can make the right decision and form policy more intelligently. Fleet lists could become much better informed," says Molden.