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One way to cut greenhouse gas emissions

Find out the pros and cons of biofuels

One way of reducing greenhouse gas emissions associated with road transport is to use lower carbon fuels.

Sales of electric and hybrid vehicles are very small currently and the majority of cars and other vehicles in service will remain petrol- or diesel-powered for many years to come. This means that reducing the carbon intensity of regular petrol and diesel can deliver significant reductions in greenhouse gas emissions across the whole of the transport sector.

Biofuels absorb CO2 from the atmosphere as the fuel source grows and can be produced from waste such as used cooking oils. Blending biofuels into regular petrol or diesel can reduce their carbon intensity.

Blending biofuels also helps meet EU and national objectives for energy security and support for the agriculture industry, though the nature of the raw materials required for current 'first generation' biofuels means that increasing production will start to threaten food production.

Bioethanol is an alcohol which can be blended with petrol and is produced by the fermentation of sugars and starches from crops such as wheat, corn and sugar beets.

Biodiesel consists mainly of fatty acid methyl esters (FAMEs) and is manufactured from a range of feed stocks including oil seed rape, waste cooking oil, palm oil, vegetable oil and animal fats.


European legislation

The Renewable Energy Directive (RED) (2009) specifies legally binding targets for EU member states' use of renewable fuels and reduction of greenhouse gas emissions.

The Fuel Quality Directive (FQD) (2009/30/EC) defines the technical standards for transport fuels to be used across the EU and also requires that fuel suppliers must meet a 6% reduction in greenhouse gas emissions by 2020, relative to 2010 baseline levels, across all fuel categories.

The FQD also establishes that ethanol may be blended into petrol up to a limit of 10% by volume.

UK legislation

The Renewable Transport Fuel Obligation (RTFO) order is the main piece of legislation in the UK which regulates the use of biofuels in transport and applies to suppliers who supply at least 450,000 litres of fuel a year.

The amount of biofuel that must be supplied increased annually until April 2013 when it reached 4.75% of total road transport fuel supplied by volume.

The RTFO also incorporates sustainability criteria defined in the Renewable Energy Directive. These criteria include minimum greenhouse gas savings and the avoidance of damage to forested areas or areas of high biodiversity and biofuels that don't meet them are considered fossil fuels for the purposes of RTFO accounting.

With the EU Renewable Energy Directive (RED) mandating that 10% of the energy from transport fuels should come from renewable sources by 2020, the UK will need at least E10 – 10% Ethanol in petrol – in the fuels mix in the future.

Fuel standards

Road fuel specifications are defined in European standards developed jointly by governments, the oil industry and the car industry to make sure that petrol and diesel are suitable for use in the wide range of vehicle and engine technologies in use on our roads today and in the future.

The standard specifications of petrol and diesel in the UK are British Standard (BS) versions of European Standards (EN) – BS EN 228 for petrol and BS EN 590 for diesel.

Initially these specifications permitted blending of up to 5% Ethanol in petrol and 5% biodiesel in diesel so that fuel suppliers could meet their obligations under the RTFO. At this level there is no issue of compatibility with car fuel systems and no requirement to mark pumps to tell customers that the fuel may contain biofuel.

This doesn't mean that all fuel actually contains 5% biofuel, only that it may contain anywhere between none and 5%.


In March 2013, reflecting changes to the EN specification, the BS specification for petrol was changed to increase the maximum level of ethanol permitted in petrol from 5% to 10% by volume.

At these higher concentrations there are potential compatibility issues with some fuel system components so the standard additionally requires that any fuel sold to the new specification must be clearly labelled on the pump as 'unleaded petrol 95 E10'. Where E10 is sold, national legislation will ensure that filling stations continue to supply an E5 'protection grade' petrol for use by vehicles not compatible with E10.

90% or more of the petrol vehicles currently in service in the UK are compatible with E10 but this of course means that a significant number are not. The government is discouraging any early switch to E10 in the UK so that the number of incompatible vehicles can reduce further (through end-of-life), and fuel producers have agreed to give three months notice ahead of the eventual introduction of E10.

Ethanol blended petrol in France

SP95-E10 (Sans Plomb 95 Octane, Ethanol 10% = Lead Free 95 Octane containing 10% of Ethanol) is already being sold throughout France.

This fuel is not suitable for use in all cars and you should check compatibility with your vehicle manufacturer before using it. If in doubt use the standard SP95 or SP98 Octane unleaded fuel which continues to be available alongside the new fuel.



When E10 is sold in the UK vehicle manufacturers and fuel suppliers will have to provide their customers with information about vehicle make and model compatibility with E10. For newer models this will be included in the handbook but for older vehicles this is likely to be via online or telephone enquiry services.

You will only need to check once if your car is compatible and will then be able to ensure that you select the correct product at filling stations – any petrol pump if the car is compatible, and any pump not labelled E10 if it's not.

It's important to check compatibility on a model-by-model basis though in general, cars built since 2000 are more likely to be compatible with Ethanol and cars built before 2000 less likely to be compatible.

Taking into account scrappage rates of cars it is likely that, by the time E10 is introduced, the majority of incompatible vehicles in use will be classic/historic vehicles maintained by enthusiasts.

Issues of compatibility with Ethanol fall into three broad areas: corrosion, material compatibility and combustion affects.

  • Corrosion – in long term storage, fuel containing ethanol can become acidic and cause corrosion of aluminium, zinc and galvanised materials, brass, copper and lead/tin coated steels.
  • Material compatibility – Ethanol's high solvency can cause problems with many seal and gasket materials used in fuel systems as well as with fibre glass resins. Besides a risk of fuel leaks, rubber components and resins can become partially dissolved, producing deposits that could foul carburettor jets. Replacement components made with ethanol-compatible materials are available.
  • Combustion – Ethanol's higher volatility can contribute to 'vapour lock' issues in older vehicles when operating temperatures are higher. Ethanol can also affect cold start performance.

Continued use of E10 in a non-compatible vehicle is likely to result in problems but a single accidental fill is not a problem. If you do accidentally fuel a non-compatible vehicle with E10 the consensus is that this would not cause any issues as long as the car was subsequently refuelled with E5. Draining the tank would not be required.


Ethanol – pros and cons
  • Ethanol is compatible with modern exhaust emissions control technologies which require ultra-low sulphur fuels, and contains oxygen so enhances combustion and reduces CO (associated with respiratory problems) and HC (unburnt hydrocarbon) emissions. It has a high octane number so helps combustion.
  • But, Ethanol's energy density is about 2/3 of conventional petrol so fuel consumption will be a little higher and volatility is increased which can contribute to higher evaporative emissions.
  • Critically Ethanol has higher solvency causing compatibility problems with rubbers and can cause corrosion in aluminium, zinc and galvanised materials, brass, copper and lead/tin coated steels.
  • Ethanol picks up water and contributes to corrosion and phase separation where ethanol and any water held in solution can separate out into distinct layers under certain conditions. Ethanol can also cause starting problems at low temperatures.
FAME – pros and cons
  • FAME is compatible with modern emissions control technologies, and contains oxygen so enhances combustion and reduces emissions of CO, HC and particulate matter. It has a high Cetane number so has good combustion properties.
  • The energy density of FAME is about 90% that of standard diesel so fuel consumption will be a little higher.
  • However, FAME increases tailpipe emissions of NOx which contribute towards acid rain, and, like Ethanol, has higher solvency so will cause issues with fuel system rubbers at higher blending rates.
  • The physical state of FAME depends on its composition – rapeseed is liquid at 0C but palm oil is solid which can affect low temperature operation.
Distribution and blending

Best practice is to blend all fuels at the refinery as this gives better control of the finished blend but petrol containing Ethanol cannot be shipped through multi-product pipelines.

Blending at the terminal – where road tankers are loaded – is more difficult and more costly due to duplication and the need for small scale dedicated transport of biofuels to terminal sites.

On balance terminal blending adds cost but is the lowest risk option – it minimises water pick-up and exposure of the fuels distribution infrastructure to ethanol.

Diesel low temperature operation

As the temperature falls, paraffin waxes in diesel come out of solution and can rapidly block fuel system filters leading to fuel starvation and engine shut down. This is affected by fuel system design and the cold flow properties of the fuel i.e. some vehicles are more sensitive than others.

Solving the issue of low temperature operation is not as simple as removing the wax – paraffin waxes have very good ignition properties and are needed to meet the Cetane requirements – a measure of diesel's combustion quality.

  • Cloud point – the temperature at which wax first appears when cooled
  • Cold Filter Plugging Point (CFPP) – the temperature at which a laboratory test filter is blocked as the fuel is cooled
  • Pour point – the temperature at which the fuel becomes solid on cooling

Oil companies can blend additives to affect low temperature operation:

  • Middle Distillate Flow Improvers (MDFI) – change the shape and reduce adhesion of wax crystals so fuel continues to pass through the filter well below the cloud point
  • Wax anti-settling additives (WASA) – reduces the size of wax crystals so that wax is less likely to settle out in long term storage in cold weather

Vehicle use can also contribute to towards the problem. Regular short trips can be more of a problem if wax trapped in the filter never melts, while longer journeys allow warm fuel via the return system to melt any wax on the filter so the vehicle stays running.

Cold flow performance with Biodiesel

The composition of FAME can affect the low temperature characteristics of the diesel into which it is blended – the physical state of FAME depends on its composition – rapeseed is liquid at 0C but palm oil is solid. This can affect the performance of any additives too.

The Base fuel, FAME and Cold flow additives must all be carefully optimised.

Advanced biofuels

Current, 'first generation' biofuels are derived predominantly from plant matter and, compared with petrol and diesel, have properties so different that using them raises fuel quality related issues throughout the supply chain. There are also concerns that there's not enough agricultural land to produce enough food and enough biofuels to meet our needs.

Second generation or 'advanced' biofuels manufactured from non-edible sources like woody crops and wood chips as well as agricultural waste such as stems, leaves and husks, will have characteristics much more like conventional petrol and diesel.

Carbon dioxide emitted into the atmosphere when biofuels are burned is offset by the amount the crop absorbed as it grew. Importantly, the net benefit will also depend on how much energy is used in production – cultivation, use of fertilisers, harvesting, transport to the processing plant, and manufacturing.

Advanced biofuels will be more efficient in farming terms as the edible parts of the crop (grain or oil) can go to the food chain and the waste to the biofuel plant. Several demonstration factories have already been built but it will be some years before production is possible on an industrial scale.


(Page updated 6 May 2014)

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