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Biodiesel and Bioethanol

Helping cut carbon and reduce greenhouse gas emissions from transport

Find out the pros and cons of biofuels

Electric and hybrid vehicles are growing in popularity but petrol and diesel will fuel the majority of vehicles for many years to come.

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

Blending biofuels can help make us less dependent on imported oil/fuel and also supports the agricultural industry, though with current, ‘first generation’ biofuels, increasing production will start to threaten food production.

  • Bioethanol is an alcohol 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.

Eco driving tips

European legislation
  • The Renewable Energy Directive (RED) (2009) sets legally binding targets for use of renewable fuels and reduction of greenhouse gas emissions.
  • The Fuel Quality Directive (FQD) (2009/30/EC) defines standards for transport fuels and requires that fuel suppliers meet a 6% reduction in greenhouse gas emissions by 2020, relative to 2010 baseline levels, across all fuel categories.
  • According to the FQD, Ethanol may be blended into petrol up to a limit of 10% by volume.
UK legislation

The main piece of legislation in the UK is the Renewable Transport Fuel Obligation (RTFO) order which applies to suppliers of more than 450,000 litres of fuel a year and requires a percentage of the fuel supplied to come from renewable and sustainable sources.

Fuel standards

Fuel specs are defined in European standards developed by governments, the oil industry and the car industry working together to make sure that petrol and diesel are suitable for use in the range of different vehicle and engine technologies in use on our roads.

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.

These initially permitted blending of up to 5% Ethanol in petrol and 5% biodiesel in diesel so that fuel suppliers could meet the RTFO.

  • At this level there’s no issue of compatibility with car fuel systems and no need 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%.E10 – petrol with up to 10% Ethanol.
  • In March 2013 the maximum level of Ethanol allowed in petrol increased from 5% to 10% by volume.

At these higher concentrations there are potential compatibility issues with some fuel system components so the standard also says that any petrol containing more than 5% Ethanol must be clearly labelled on the pump as ‘unleaded petrol 95 E10’. 

Where E10 is sold, filling stations should continue to supply an E5 ‘protection grade’ petrol for use in vehicles that aren’t compatible with E10.

More than 90% of petrol vehicles on the road are compatible with E10 but this of course means that a significant number are not.  The government discouraged an early switch to E10 in the UK so that the number of incompatible vehicles can reduce further (through end-of-life).

E10 in France

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

  • SP95-E10 isn’t suitable for all petrol cars.
  • Check compatibility with your vehicle manufacturer before using it.
  • If you’re not sure, use the standard SP95 or SP98 Octane unleaded fuel.
Possible compatibility issues with Ethanol

Petrol cars made since 2000 are more likely to be compatible with Ethanol than cars made before but it’s important to check.

When E10 is introduced, vehicle manufacturers and fuel suppliers will have to provide information about vehicle compatibility:

  • For newer models this will be in your handbook
  • For older vehicles this is likely to be via online or telephone enquiry services.
  • You’ll only need to check once.

If your car’s not compatible but you run it on petrol with a higher concentration of Ethanol, possible Issues fall into three broad areas: 

  • 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.
Misfuelling with high Ethanol fuels

If you keep using E10 in a non-compatible vehicle it’s likely to result in problems but a single accidental fill isn’t a problem and there should be no need to drain the tank.

Pros and cons of Ethanol
  • Ethanol is compatible with modern exhaust emissions control systems and contains oxygen so enhances combustion and reduces CO and HC 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.  Ethanol can also cause starting problems at low temperatures.
Pros and cons of FAME (biodeisel)
  • FAME is compatible with modern emissions control systems, and contains oxygen so enhances combustion and reduces emissions of CO, HC and particulate matter. It has good combustion properties.

But

  • FAME has about 90% the energy density of standard diesel so fuel consumption will be a little higher.
  • 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.
Diesel low temperature operation

As it gets colder, paraffin waxes in diesel come out of solution and can quickly block your fuel filter leading to fuel starvation and engine shut down.  

The design of your fuel system, the cold flow properties of the fuel and how you use your car can all contribute to make some vehicles more sensitive than others:

  • Regular short trips can be more of a problem if wax trapped in the filter never melts
  • Longer journeys allow warm fuel via the return system to melt any wax on the filter so the vehicle stays running.

Solving the issue of low temperature operation isn’t 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. The Base fuel, FAME and Cold flow additives must all be carefully optimised.

Advanced biofuels

Current, 'first generation' biofuels are made mainly from plant matter:

  • Compared with petrol and diesel they 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 farm land to produce enough food and enough biofuel 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. Several demonstration factories have already been built but it will be some years before production is possible on an industrial scale.

  • Carbon dioxide emitted into the atmosphere when biofuels are burned is offset by the amount the crop absorbed as it grew.
  • The net benefit depends 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/oil) can go to the food chain and the waste to the biofuel plant. 

22 May 2017

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