A fuel is a substance which gives heat energy on combustion. A fuel contains carbon and hydrogen as main combustible elements.

Calorific value of fuel: The amount of heat liberated in Kilocalorie or Kilojoules by the complete combustion of 1 Kg of fuel.

Fuels can be divided into three main categories

1.      Solid fuels

2.      Liquid fuels

3.      Gaseous fuels

Solid fuels: Solid fuels left some ash or residue after combustion. The solid fuels and their calorific values are given below.

Liquid fuels: Most of the liquid fuels in use are the hydrocarbons which exist in the liquid phase at room temperature. The liquid fuels and their calorific values are given below.

Gaseous fuels: Some of the gaseous fuels exist naturally at room temperature and some are made by the treatment of coal. The gaseous fuels and their calorific values are given below.