Throughout the developed world, cars and commercial vehicles use a great deal of fossil fuel and release pollution into the atmosphere – notably CO2, thought to be causing climate change. The need to switch to other fuels is clear, and some alternatives are already available. Biofuels have been particularly well received by motorists because they bring significant environmental benefits and, importantly, can be used in existing vehicles with little or no modification.
The two types of biofuel supplied for use in motor vehicles are bioethanol, a denatured alcohol that can be blended with petrol, and biodiesel, which is oil-based and can be used as a replacement for normal diesel.
Bioethanol – How It’s Made
Bioethanol is derived from plant material containing sugars and starches. The source is normally agricultural crops grown specifically for conversion to biofuel, but it could also be waste matter – crop residues or organic household waste.
Like other alcohols, bioethanol can be made from grains or fruit, and also wood. Sugar beet and wheat are used in the UK, whilst around the world common alternatives include corn and potato. Sugar cane, used extensively in Brazil, has an extra advantage in that the fibrous waste, or bagasse, can be used to provide the thermal energy required to evaporate the cane juice. In the UK, manufacture of bioethanol from sugar beet began in 2007.
Bioethanol burns to produce very significantly low levels of CO2 than petrol.
Bioethanol – How It’s Used
For use in motor vehicles, bioethanol is always blended with petrol. Two different petrol/ethanol mixtures are available in the UK. One is a blend of 5 per cent; this is the maximum percentage of ethanol that petrol suppliers are allowed to include in their ordinary unleaded petrol under current regulations, although there is speculation that the limit may soon be increased to 10 per cent. A blend of 5 per cent has no noticeable effect on vehicle performance, and a large proportion of the petrol sold on UK forecourts contains 5 per cent bioethanol. The alternative is an 85 per cent blend, marketed as E85, and this is only suitable for flexfuel vehicles.
Ethanol is higher octane and more corrosive than petrol. In order to run on an 85 per cent mixture, cars must be adapted to prevent engine damage. Because E85 has limited availability, it would be impractical to make vehicles that use only E85; they need to be able to use petrol as well. A number of car manufacturers have designed flexible fuel cars, known as ‘flexfuel’, that run equally well on either fuel. Potentially, the higher octane rating of E85 could be maximised to achieve enhanced performance, but this entails making advanced modifications to the engine settings, and at the time of writing only one manufacturer markets a flexfuel car that actually performs better on E85 than on standard petrol.
Like bioethanol, biodiesel can be produced either from purpose-grown crops or from waste. In Europe, rapeseed oil is grown extensively as a biofuel crop. Vegetable oils and waste cooking oils and fats are also used, and kits are sold in the UK that enable individuals to convert waste oil into biodiesel.
Most older diesel engines can run on pure biodiesel, although if a vehicle is to be run for a long time on a 100 per cent blend some precautions might be necessary, such as replacing rubber hoses with corrosion-resistant plastic. For modern diesel vehicles, biodiesel is normally blended with normal diesel in varying proportions, according to manufacturer specifications.
Cars using crude-oil diesel produce less CO2 that petrol cars, but more particulate emissions. Using biodiesel, CO2 is cut down still further and particulates are also reduced; biodiesel contains more oxygen, so combustion is more complete. The higher the proportion of biodiesel in the fuel, the cleaner the emissions.
Advantages of Biofuels
Bioethanol and biodiesel produced from fuel crops can be classed as carbon-neutral because whilst the crops from which they are derived do emit CO2 as they burn, they absorbed an equivalent amount of CO2 as they grew. These fuels can also be classed as a renewable energy, as long as the cropping cycles are sustainable. Producing biofuels from organic waste can have the extra advantage of reducing the amount of material sent to landfill.
However, there are political, economic and conservationist issues around using agricultural land for biofuel crops, and waste material alone could never provide anywhere near enough biofuel to meet our needs. Certainly the implications for food production and biodiversity suggest that this is not, in fact, a permanently sustainable solution; but in the short term, if we are able to produce moderate quantities bioethanol and biodiesel without affecting the natural or economic balance, this offers an accessible means of achieving a reduction in carbon emissions.