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
- Solid fuels
- Liquid fuels
- Gaseous fuels
Solid fuels: Solid fuels left some ash or residue after combustion. The solid fuels and their calorific values are given below.
| Fuel | Calorific Value (Kcal/kg) |
| Wood | 2500 |
| Peat | 3500 |
| Lignite Coal | 3000 |
| Bituminous Coal | 7500 |
| Anthracite | 8500 |
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.
| Fuel | Calorific Value (Kcal/kg) |
| Gasoline | 11,200 |
| Paraffins | 11,100 |
| Diesel | 11,000 |
| Fuel oil | 10,500 |
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.
| Fuel | Calorific Value (Kcal/kg) |
| Coal gas | 7630 |
| Coke oven gas | 5100 |
| Producer gas | 1200 |
| Blast furnace gas | 970 |