Fuels – A Glossary
Petrol is a fossil fuel refined from crude oil. It evaporates easily and is mixed with air before it enters the engine to burn more cleanly.
Diesel is also a fossil fuel that is refined from crude oil. It does not evaporate easily and is ideally suited for burning in diesel engines.
Biofuels are produced from biological, renewable sources such as crops. They don’t necessarily produce less CO2 emissions when they burn, but their ‘lifecycle’ is usually greener as the crops themselves remove CO2 from the atmosphere when they’re growing. Currently there are three types of bio-fuel: biodiesel, bioethanol and biogas.
Biodiesel is the biofuel equivalent of diesel and is generally produced from ‘oily’ crops like rapeseed, sunflower or palm, or from recovered cooking oil. These oils are thicker than fossil diesel and need processing (called esterification) in order to make them less viscous and more able to mix with air and burn cleanly. A biodiesel blend (with 95% fossil diesel) is currently available from around 100 filling stations in the UK and can be used by any vehicle without adaptation.
Bioethanol is the biofuel equivalent of petrol and is generally produced from starchy crops like wheat, sugarbeet or sugar cane. It has the potential to be made from virtually any organic substance, for example drinking alcohol, grass, wood and green bits of municipal solid waste, but this technology is not yet proven on a commercial scale. At the moment, the fuel available is a fossil petrol mix with up to 5% bioethanol (which can be used by any vehicle without adaptation), and a higher blend called E85.
E85 is a blend of 85% bioethanol with 15% fossil petrol and is used to fuel specially designed vehicles called ‘flex fuel’ vehicles. These vehicles can run on petrol containing anything from 0% to 85% ethanol.
Biomethane is the biofuel equivalent of Compressed Natural Gas. It is generally produced by collecting methane naturally emitted from landfill sites or other forms of rotting vegetation. Biomethane is only suitable for use in CNG-powered vehicles.
Petroleum Gas is a fossil fuel that is refined from crude oil. It is used in specially designed or modified ‘bi-fuel’ vehicles capable of running on either petrol or LPG. LPG produces more CO2 than diesel, but less than petrol. When it comes to air quality pollutant emissions it produces more than petrol, but less than diesel.
Compressed Natural Gas is methane from fossil sources and is stored in special fuel tanks under pressure. This ensures enough fuel for an acceptable driving range in specially designed or modified vehicles. These CNG cars are usually ‘bi-fuel’ vehicles capable of running on either petrol or CNG. CNG produces less CO2 than petrol, is similar to or slightly less than diesel, and generally produces fewer air quality emissions than diesel, but only slightly less than petrol.
Liquified Natural Gas is methane from fossil fuel sources. It is stored at extremely low temperatures on the vehicle in sufficient quantities to ensure an acceptable driving range when it liquefies.
Electricity to power vehicles is generally taken from the national grid and stored in batteries on the car. Electric vehicles have no tailpipe emissions but electricity generation by power stations does produce CO2.
Hydrogen can be used as a vehicle fuel either in an internal combustion engine or in a fuel cell. In a fuel cell the only emissions would be water, with only a small amount of air quality emissions from a normal engine. However, hydrogen production (either from oil refineries or from electrolysis of water) is an energy intensive process and as a result there is not necessarily any ‘lifecycle’ CO2 emission saving by using hydrogen as a road fuel. To achieve lifecycle greenhouse gas emissions savings, hydrogen needs to be produced from renewable energy sources.