# What are fossil fuels and how do they differ from other types of fuel? Which fossil fuels are used in diesel engines?

Fossil fuels are the remains of prehistoric animals and plants and are found below the surface of the earth; they may be solid, liquid or gaseous.
S Solid fuels. Coal is the most important solid fuel used commercially.
Liquid fuels of a wide variety are obtained from distillation and other processes carried out on crude oil. The products obtained are essentially engine fuels, j boiler burner fuels, and lubricants.
Note—The oiHndustry is also a large supplier of chemicals used in other industries such as plastics, paints and compositions, synthetic rubbers and the | like.
1 Gaseous fuels may exist naturally in the ground or be produced from coal or
crude oil. Liquefied petroleum gases (LPG) are increasingly used.
! The fossil fuels are essentially carbon-hydrogen compounds. The energy is
derived from them by the exothermic action of converting the carbon to carbon dioxide and the hydrogen to water, which will be in the form of steam at the end – of the combustion process.
! The other types of fuel used are nuclear, which are fissile materials used in a
| reactor. One of the isotopes of uranium is commonly used. „
The fuels used in diesel engines are the gas oils and diesel oils which boil off from crude at temperatures between approximately 200°C and 400°C, or blends of diesel oil and residual fuel which have higher boiling points.
Note Liquefied petroleum gases must be stored under pressure or in refrigerated conditions, since their boiling points are low.