Bioethanol made from sugar or starch can replace petrol, but only a mix of about 5% bioethanol with petrol can be used in an existing car without any problems. Most petrol sold in the UK already contains 5% ethanol, to meet the Government’s Renewable Transport Fuels Obligation (RTFO).
Going beyond this is difficult for both technical and environmental reasons.
A high proportion of bioethanol in petrol may damage rubber seals and aluminium parts in the engine. Some 'flex-fuel' vehicles were designed with hardened components, non-rubber seals and larger fuel lines to cope with the abrasiveness of the fuel. Wider use of bioethanol would also require modification of the fuel supply infrastructure: pumps, tankers and storage facilities.
However, the main problem is that carbon emissions from biofuels can be very high, due to land use changes such as deforestation and from the fuel and fertiliser needed to grow and process the crops. When all factors are included, it is unlikely that biofuels have lower greenhouse gas emissions than the fuels they replace. There are also concerns about impacts on biodiversity and water availability, and competition for land needed to grow food.
In our Zero Carbon Britain project, we advocate the use of electric vehicles along with a reduction in private car use as the best way to reduce carbon emissions from road transport. See the report for much more about the reasons for this.
Making ‘second generation’ biofuels from wood or grasses causes fewer problems, but there will still be limits on the land available. If some biofuel can be produced sustainably, it’s best used where electricity cannot be – such as shipping, some heavy goods vehicles and farm machinery, and aviation.