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One of the biggest
impacts of vehicle use is tailpipe emissions. Most attention is focused on
Carbon Dioxide (CO2) emissions as these are a major contributor to
global warming. CO2 emissions are generally related to fuel type
and engine size. More stringent European emission standards are driving down
the level of CO2 emissions. Driving behaviour (see
page on responsible driving techniques) also has impacts on CO2 emission with increased emissions coming at higher
speed.
Certain fuel types give less CO2 emissions than others.
Diesel engines often
have lower CO2 emissions and better fuel economy than petrol engines, but emit
other pollutants such as Nitrogen Oxides (NOx) and particulates which effect
air quality. When and where you use a diesel engine is important in tackling
air quality issues. For example, when driving at speeds on a motorway or major
road a diesel engine is likely to have less of a negative impact due to lower
CO2 emissions. However,
when driving in a congested, urban area, a diesel engine is likely to have
more of a negative impact due to emissions particulates.
Liquid Propane Gas (LPG) gives good fuel economy but the advantage it had of lower CO2 emissions has been eroded in recent years by the increased efficiency of petrol and diesel engines due to the requirement to meet Euro IV emission standards by 2007. LPG is however much cleaner than diesel when it comes to Nitric Oxides and fine particulates, the average diesel emitting around 120 times as many as an LPG powered vehicle.
See www.lpg-vehicles.co.uk for more information.
Electric
cars
are powered by batteries, recharged from an electric output. As a result of
this electric cars have no tailpipe emissions, they are free from local
pollution and CO2 emissions, but they aren't entirely pollution-free,
especially if they are recharged from an electric power grid that burns
significant quantities of fossil fuels like coal.
Despite being touted as a possible solution to vehicle emissions issues, electric cars have not taken off, due to a number of reasons such as cost, limited range and availability of charging stations. Some examples of electric cars are the Lexus 2045, Nissan Altra, and the G-Wiz.
Fuel
hybrid vehicles employ a parallel hybrid system in which a petrol engine provides
the main power to the vehicle with an electric motor assisting when needed.
The efficiency of the technology leads to lower CO2 emissions than from
ordinary petrol or diesel vehicles. Examples of such hybrid vehicles are the
Toyota Prius, Honda Insight or Lexus
GS 450h
Such vehicles are currently considerably more expensive than conventionally powered cars. It is expected that prices will fall as the technology becomes more commonplace. Much work is being done to encourage the development of low or zero carbon vehicles and fuels through the LowCVP group.
Biofuels The “Renewable Transport Fuel Obligation” (RTFO) places an obligation on fuel suppliers to ensure that a
certain percentage of their aggregate sales are made up of biofuels from April
2008. The effect of this is to require 5% of all UK fuel sold on
Biodiesel uses vegetable oil as a substitute for conventional diesel and can reduce CO2 emissions by around 50%, although it can increase NOx. Most diesel engine cars will operate well on a 5% mix (B5) but manufacturers warranties may be invalidated by 100% biodiesel (B100) due to possible damage to certain materials. Having a secure and sustainable local supply may also be an issue, although it is possible to make it yourself at home (see www.journeytoforever.org/biodiesel_make.html#3choices). Large scale production of biodiesel, whether from new vegetable oil or from recycled oil, is subject to regulation, while production of less than 2,500 litres per year is currently duty-free - the Environment Agency details the legal situation.
Biogas is a renewable alternative fuel, which is produced by breaking down organic matter by a process of microbiological activity. Basically this means that rotting municipal waste, food waste or sewage (both human and animal) is turned into gas by means of "anaerobic conversion" in a digester.
It's generally accepted that biogas gives an average 95% carbon dioxide reduction (well to wheel) in comparison to diesel whilst also delivering 80% lower NOx emissions and zero particulate emissions. It can also be argued that the use of biogas creates a carbon reduction of greater than 100% as the organic matter would have naturally put methane, a greenhouse gas 21 times more potent than carbon dioxide, into the atmosphere. Instead the methane is converted into carbon dioxide when burnt in the engine. Thus, developing this fuel would also provide environmental benefits by lowering the need for landfill and allowing gas capture at sewage works.
Although availability is currently limited several refuelling stations linked to the HGV industry are planned for the next 5 years. see www.energysavingtrust.org.uk/fleet/technology/alternativefuels/biogas
Bioethanol is a liquid biofuel made from fermented, distilled starch plants, such as corn or sugar, and is widely used in Brazil. It can be used on it's own or blended with petrol, although higher E85 blends require modification of the vehicle. It is generally accepted that on a well to wheel basis, bioethanol gives a 70% carbon dioxide reduction versus petrol. This means that a 5% blend produces 3.5% less carbon emissions, whilst an 85% blend (like E85) would achieve a 50% reduction. Bioethanol is not widely available in the UK at this time but looks set to increase as car manufacturers begin to produce vehicles that can run on all blends up to 85%.
The Future? - There is much interest in developing alternative fuels and technologies, and a great deal of investment in these areas at the moment. Hydrogen and electric technologies are likely to move forward, as well as the development of hybrid vehicles running on combinations of any or all of the above.
Biofuels
are generating a lot of controversy, as crop production threatens to compete
with food production. There is also debate within the scientific community as
to whether the CO2
produced in cultivation
negates any benefit from lower tailpipe emissions.
Biogas offers the least environmentally damaging prospect as it is created from waste material that would otherwise have a negative impact on the land and the atmosphere.
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