There are many diffirent types of fuels. Anything that burns can be called a fuel, although "fuel" usually means materials that are commonly used as fuels. Wood, coal, natural gas, and gasoline are all examples of common fuels. Fuels are usually classified as solid,liquid, or gaseous. Solid fuels, such as coal can be stored in big piles and moved in tank cars, or pipelines. Gas fuels may be kept under pressure in extra-strong containers. They may be changed to a liquid for transporting in tanks, or they may be sent thousands of miles through pipelines as a gas. Today, burning fuels-mainly coal, oil, and gas are still used for heating and cooking. They are also used in enormous amounts in powerhouses and to drive automobiles, ships and airplanes. The burning of so much fuel has resulted in air pollution in many places, and in the threat of a worldwide fuel shortage. As fuels are used up at ever-growing rates, scientists and engineers are working to develop other possible sources of heat to meet the worlds needs.
Scientists believe that coal, oil, and natural gas were formed from plants that lived in swamps millions of years ago, and from small animals that fed on these plants. Firewood and charcoal may come from trees growing now.The energy in these fuels came originally from the sun.Plants trap energy from the sun's rays and use it to build their tissues.Burning wood and charcoal releases energy that has been stored up by plants in this way.When we burn coal or oil, we use energy stored up by plants that lived millions of years ago.
Fuels may be used in various ways to produce power.One way is to use the heat from burning fuel to turn water into steam.The steam is then used to run steam engines or turbines.Sometimes the steam engine or turbine is used by itself, as in a steam locomotive or a turbine-driven ship.Usually, the steam engine or turbine is used to drive an electric generator that supplies power for electric motors and other electric equipment.
