10th Class Science Sources of Energy Fuel

       Fuel

Fuel are those materials which produce heat energy on burning. For example, the fuel like wood, LPG, coal, petrol, diesel, etc produces heat energy while they burn. All fuels produce heat energy, on burning, in different amounts. It depends on the calorific value of the fuel. The calorific value of the fuel is defined as the amount of heat produced by burning of a unit mass of fuel. For example the calorific value of the fuel is 33000 j/g. Hydrogen has highest calorific value of 150 kj/g and hence it can be the best sources of the fuel. H

Most of the fuel which contains hydrogen and carbon has high calorific value than others. Before a fuel catch fire and starts burning it must be heated to a certain minimum temperature. The minimum temperature to which a fuel must be heated before it catches fire and starts burning is called ignition temperature.                                                      

The good fuel has certain characteristics which are as follows:             

• It should have high calorific values, so that, heat produced per unit volume of burning of fuel is maximum.
• It should be cheap and easily available in the place.
• It should have low ignition temperature.
• It should be easy to transport and easy to store,
• It should not leave any residue after burning.
• It should not cause environmental pollution and release smoke.
• It should be safe to handle.

           Fossil Fuel

The fuel, which is obtained by decomposition of remains of the dead plants and animals buried deep inside the earth crust, is called fossil fuel. Coal, petroleum and natural gas are all fossil fuels. The fossil fuels are also the major sources of energy for generating electricity in power plants. The natural gas consists of mainly methane with small quantities of ethane and propane. In fact it contains methane up to 95%. It is found deep under the earth crust, either along with oil or alone. It is formed under the earth by the decomposition of vegetable matter lying under water by anaerobic bacteria in absence of oxygen. The other important fossil fuel is petroleum which is dark colored viscous and foul smelling crude oil. It is found under the earth crust trapped in rocks. The crude oil petroleum is a complex mixture of several solid, liquid and gaseous hydrocarbons mixed with water, salt and earth particles. It also     contains small amount of other carbon compounds containing oxygen, nitrogen and sulphur. Since it contains mixture of alkane hydrocarbon with water, salt and earth particles, it cannot be used as a fuel in the same form. Hence it needs to be purified before being used. The process by which the different fractions of petroleum can be separated is known as fractional distillation.