Fuel Types

Types of Fuel

Various types of fuel are available dependent on a vehicles demands. However, with increasing fuel prices and the inevitable supply and demand issue regarding hydrocarbons, there is a greater interest in alternative fuel supplies which are renewable and becoming less expensive to manufacture.

Liquid Hydrocarbons

These come from fossil fuels which are non-renewable sources of energy. They are the petroleum fuels from which the different octanes of petrol are made and from which diesel is produced.

Petrol can be subdivided by octane ratings. These describe how resistant a fuel is to detonation – a form of combustion that is also known as pinging or knocking. The higher the anti-detonation value, the greater the octane rating of the fuel and in turn, the greater its ability to resist knocking. Higher performance engines have higher compression ratios which result in a higher risk of detonation. This indicates that they need to use a higher octane rating to avoid this. In contrast, a lower octane number implies easier autoignition, which is undesirable in spark-ignition engines (petrol engines), but preferred in diesel engines since these do not require a spark plug to ignite the fuel. Diesel fuel is measured by the cetane number CN and not the RON. The higher the cetane number, the higher the risk of detonation, which is desirable.

In the past, in order to increase the octane rating, fuels had lead added to them to further prevent detonation, especially when used in highly pressurised combustion engines. Since it was realised that leaded petrol caused environmental problems and could not be used with catalytic converters, alternatives were sought, such as the use of alcohol and aromatic hydrocarbons.

The octane number (the Road Octane Number, RON) is what is usually quoted at petrol stations. The RON is an average of the research octane number and the motor octane number (MON). Since the MON is tested under more strict conditions it is lower than the research octane number.

The most commonly available fuels on UK forecourts are:

  • Unleaded – 95 RON
  • Super unleaded – 98 RON
  • Leaded – 98RON
  • Diesel – minimum 51CN


Due to our awareness for the need to protect the environment and delay the rate at which current, non-renewable fossil fuels are being used, other sources of fuel which are both environmentally friendly and renewable are being researched and brought into use. With time, these are bound to become more economical and are planned to replace the standard forms of fuel on the forecourt.

Alternative Fuels

These are cleaner fuels that offer environmental benefits as well as help to reduce fuel costs.

Lower Sulphur Fuels

These are used for diesel engines to help give off lower sulphur emissions and hence, allow diesel vehicles to run on cleaner fuel. In the UK, lower sulphur diesel fuels contain only 10ppm (compared to the standard sulphur content of 50ppm). This lower sulphur form of diesel is now widely available in the UK.

Fuel Additives

Certain additives can help improve emissions by increasing the octane rating number, or by acting as lubricants or corrosion inhibitors. They help vehicles achieve better power and work in a more efficient manner. The typical types of fuel additives are corrosion inhibitors and antioxidants.

Liquid Petroleum Gas (LPG)

This is a blend of propane and butane made from methane gas or from the by-products of oil-refining. It is suitable for smaller vehicles such as cars and light vans that have higher mileage or are mainly used in city centres. The cost to run a LPG vehicle is about two-thirds that of petrol car and the equivalent to a diesel car. New LPG cars can be purchased, but it is possible to convert petrol vehicles to run on LPG at a cost of around £2000.


These are produced from the oil of crops such as oilseed rape, sunflower and soybeans. Can be used as a 5% fraction in existing diesel engines with no need for modification. Using bio-diesel will reduce the amount of CO2 your engine produces by up to 60%, resulting in lower pollutants entering the environment. However, bio-diesels do produce oxides of nitrogen which has a tendency to form a smog. Higher amounts than 5% additions can be used with the engine requiring limited modifications but this may affect vehicle warranty.

Pure Plant Oils (PPO)

Few petrol stations in the UK offer this form of fuel which is very similar to diesel. Vehicles are powered on fuel made from crushed and purified plant oils such as oilseed rape, palm and nut, but a heater must first be added to the fuel line to help the oils flow.

Biogas – Compressed Natural Gas

Produced by the breakdown of organic materials by anaerobic activity (no oxygen required) to produce methane. This can be produced by the rotting of food or municipal waste or sewage. On average, they can reduce CO2 emissions by 95% compared to diesel engines and cause nitrous oxide production to be reduced by 80%.


This is very much a fuel of the future which is currently only used in prototype vehicles. It is produced by the breakdown of hydrocarbons or the electrolysis of water. This form of fuel is almost pollution-free but only if renewable resources are used, such as wind and solar power. At the moment, these vehicles are much more expensive than petrol-run ones