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Fuel Systems

Fuel Types

Internal combustion engines can run on a variety of fuels including:
Compression Ignition:
Diesel (fossil fuel kerosene)
Spark Ignition:
Petrol (gasoline)
CNG (Compressed Natural Gas)
Ethanol & methanol (ethyl & methyl alcohol)
Butanol & propanol mixed as LPG / Autogas
(Butane & Propane, Liquified Petroleum Gas)


Pan of frying oil It seems that well soon all make our own diesel at home from the waste fat from the local chippie! There is tax on biodiesel but at a lower level than diesel from fossil fuel sources. Thus it is cheaper and has environmental benefits. Vehicles may have problems with rubber components in the fuel system. The main problem, with current sources, is that the car smells like a chip shop!

Compressed Natural Gas (CNG)

Gas burner There are vehicles which run on the same gas that you have in your house. The disadvantage (compared with LPG) is that a very high pressure is needed to liquify the gas at normal temperatures. This means that filling stations have to install very expensive compressing equipment, and that the vehicle tank is heavier because it has to withstand the very high pressure.


Glasses of alcohol Although fossil fuels have become the dominant energy source for the modern world, alcohols have been used as a fuel throughout history. The first four aliphatic alcohols (methanol, ethanol, propanol, butanol) can be synthesized and have characteristics which allow them to be used in current engines. (Generally speaking, the chemical formula for alcohol fuel is CnH2n+1OH. The larger n is, the higher the energy density.) Dont drink this stuff, though, its full of other nasty additives!
Alcohols burn more completely than petrol because their molecules contain oxygen, so the only products of alcohol combustion are water, carbon dioxide, and heat. Alcohols can be made from organic materials such as grains, fruit or wood, or derived from fossil fuels. Brazil is well known for using alcohol fuels made from sugar cane.

Biological v Fossil

Sugar cane Alcohol fuels can be produced from either biological or fossil fuel sources. When obtained from biological sources, they are known as bioalcohols (e.g. bioethanol). There is no chemical difference between biologically produced alcohols and those obtained from other sources. Bioalcohols are still undergoing development - use of optimised crops with higher yields of energy will help improve their usefulness as fuel, although there are environmental concerns over the risk of deforestation to make way for biofuel crops.

Ethanol and Methanol

Alcohol filler pump The energy densities of Ethanol and Methanol are about 64% and 53% of petrol and 56% and 46% of diesel. They can be used either as sole fuels or mixed with petrol. Most contemporary petrol cars will run on E10, a 10% mixture of ethanol to petrol (Gasohol in the USA!). Cars have been developed which run on higher proportions of alcohol, typically E85. The 5% mix can be used in most petrol vehicles but the 85% mix is limited to a small number of current vehicles. Ethanol differs from petrol in car engines: it has a higher octane rating, is more corrosive, cleans old deposits away (filters may need changing), may create flow problems and can make starting more difficult. Older vehicles are likely to have problems with rubber components in the fuel system.

Availability of Alcohol Fuels

In the UK tax concessions in 2005 caused a 5% ethanol mixture to enter the retail market. A firm called Greenenergy pioneered this and Tesco are retailing the fuel (SE England). In 2006 Morrisons, started selling E85 bio-ethanol in East Anglia. The trend should continue prompted by government action.

Dual Fuel (Ethanol) Engines

"Flex" engines work with petrol, alcohol or any mixture of both fuels. In Europe, Ford has a Flex-Fuel Vehicle (FFV), in its Focus range. In Sweden tax concessions mean that Saab and Volvo are using the relevant technology.

LPG (Butanol and Propanol)

LPG filler pump LPG (Liquified Petroleum Gas, also known as Autogas) is a mixture of Butane & Propane, and is readily available from some 1500 outlets around the UK. The number of outlets is increasing, but you can even have your own tank installed (just like your oil tank) and fill up at really low cost at home! A vehicle LPG system consists of a tank, a vapouriser to turn the liquid into gas (like a carburettor does for petrol), injectors to get it into the engine and some valves and filters. More than 20,000 vehicles use LPG in the UK because it has a number of advantages:

1It is easy to liquify at normal temperatures.
2It is around half the price of petrol or diesel.
3It has a number of environmental benefits.

Environmental Considerations

Most people fit LPG to save money. However, among the environmental benefits are lower pollution, and lower cost to provide the fuel. LPG produces significantly less carbon monoxide, hydrocarbons and oxides of nitrogen than petrol and emits 90% less particulates than diesel engines. LPG is at present a waste product of the oil industry, so the "Well to Wheel" environmental cost is lower than petrol or diesel.
Key to graph of pollutants Graph of pollutants Harmful road fuel pollutants expressed as percentages.
[Acknowledgement: CLS Dual Fuel Ltd]

Important note:

The information above is derived from several public sources.It should not be construed as definitive and is presented for background knowledge only.Specific and qualified expert advice must be obtained before reliance is made on the facts presented.


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