Moving to a life cycle assessment of vehicle emissionsNovember 15, 2011
The ‘greenness’ of a car is currently based on its ‘tailpipe’ CO 2
emissions; however this doesn’t allow for the CO 2
in its manufacture; so is a rating based on the entire CO 2
produced over a vehicle’s lifetime, including manufacture, a better idea?
That debate was the focus of a conference held in London on 14 November 2011 hosted by the Low Carbon Vehicle Partnership (LowCVP) and the Institution of Mechanical Engineers (IMechE). A number of speakers gave presentations on this issue, with the aim of seeing if this was the correct road to go down, and if so, what would need to be done, and how long would it take us to implement such a new system. The outcome certainly provided a lot for the car industry to talk about.
The first issue to clarify is what constitutes the whole vehicle life cycle. There are three overall elements – vehicle manufacture; vehicle use – which includes both the production of its fuel and the use of its fuel by the vehicle; and vehicle disposal. Within these broad headers there are over 100 individual elements that contribute to a vehicle’s life cycle environmental impact. None of this includes what the driver will do with the vehicle, ie. how it will be driven.
At the moment automotive engineers are driven by 2015’s target of 130 g/km CO 2
average fleet tailpipe emissions in Europe. The plan is that this will reduce to 95 g/km CO 2
by 2020 – with significant penalties for manufacturers who do not hit these targets. There’s also legislation for ‘regulated emissions’ such as carbon monoxide and nitrous oxide in the form of the ‘Euro’ standards. And there’s the End of Life Vehicle Directive – currently requiring 85% of a car to be reused or recovered at the end of its life.
So there’s lots of legislation, but nothing to help with the comparison of the environmental impact of all types of different technologies over the lifetime of a vehicle. And when we say lifetime, the most commonly accepted definition of this is 150,000 km of use, with fuel usage and associated emissions based on the NEDC fuel economy cycle.
Traditionally, around 80% of the energy that a petrol car uses in its lifetime is accounted for by the fuel that it uses, with the remaining 20% being in manufacture and disposal. For an efficient diesel emitting 120 g/km CO 2
, this proportion becomes 75% v 25%. Hybrids have a lower overall carbon footprint; they use less fuel, but have more embedded emissions in their production. A plug-in hybrid emitting 78 g/km CO 2
has a split of 57% v 43%. An electric car emitting 45 g/km CO 2
is even more efficient in its use, but has an increased carbon footprint in its manufacture, mainly due to its battery; the split becomes 43% in use, compared to 57% in manufacture. So as cars become more efficient, their overall emissions are decreasing, but the carbon embodied in their manufacture is increasing – hence the need for a debate to work out the best way of conveying the real environmental impacts of all types of vehicle technologies.
Looking at plug-in vehicles, there are other variables, such as which country you’re in; for instance the emissions from energy generation in France is technically lower than that in the UK because of the significant nuclear energy component. However even in just the UK there are differences in the carbon make-up of the energy mix from month to month – and even hour to hour.
We already have standards for lifecycle assessment and carbon footprint calculations, and manufacturers have been carrying out work in this area for 10-20 years. So, changing to a life cycle assessment of vehicle emissions sounds like the way to go.
However, there are problems. Manufacturers may have data, but they won’t have been using the same input data and assumptions as each other. So to implement a life cycle system, the industry would have to standardise all of its data. The industry is also starting to use new materials, such as lightweight carbon fibre etc; such materials are often difficult to calculate their embedded emissions. And so far, the focus of data has been on greenhouse gas emissions; but what about areas such as the use of natural resources and other wider environmental impacts? This gets even more complex when looking at biofuels, where there can be impacts of factors such as land use change created when growing biofuels. Such issues can go on and on; where do you stop?
Another factor in all this is the NEDC fuel economy testing cycle. This data would be utilised for the ‘use’ stage in a life cycle assessment. However it is acknowledged that the NEDC cycle doesn’t provide an accurate reflection of the real world fuel use of cars. The NEDC cycle is based on four urban drive cycles, and one extra-urban drive cycle, with a maximum speed of 100 km/h, except for one brief peak at 120 km/h. Because it’s based mainly on the urban cycle, manufacturers are focusing on reducing urban drive cycle emissions through the use of technology such as stop-start systems. All this means that to make the lifecycle assessment as accurate as possible, the NEDC cycle should also be revised, to include elements such as more motorway use or a constant speed element, an allowance for extra weight/passengers, and use of electrical items such as air conditioning and lighting. Currently large cars are closer in real life use to the NEDC data than small cars, and this is likely to be even more the case if the above changes were implemented in the testing cycle. Cars emitting 110 g/km according to the NEDC test have been found to emit over 40% more emissions in real life.
A final issue is ‘international carbon flows’. This basically means that when cars are manufactured in, for instance, the Far East, and transported to Western Europe and North America, the carbon flows from East to West also. This is another potentially complex factor that would need to be taken into account with any life cycle carbon emissions calculation.
The overall conclusion of the conference was that although it is generally acknowledged that we need to move to a life cycle assessment of vehicle emissions, due to the many input variables currently having no standardised data, a life cycle system is just too complex and won’t happen in the near future. So as a baseline measure to compare cars, for the time being it looks like we’re stuck with the NEDC test and its seemingly increasing gap from real life economy and emissions figures.
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