Calorific value is one of the most important characteristics of a fuel. It judges the efficiency of fuel.

Calorific value is defined as "the total quantity of heat liberated, when a unit mass or volume of the fuel is burnt completely."

Units of heat

1.      Calories: amount of heat required to raise the temperature of 1 gm of water by 1⁰C is known as calorie.

2.      Kilo-calorie (kcal): amount of heat required to raise the temperature of 1 kg of water by 10C is known as kilo-calorie.

                                            1 kcal = 1000 cal.

3.      Centigrade heat unit (C.H.U): it is defined as the amount of heat required to raise the temperature of 1 pound (lb) of water by 1 ⁰C.

4.      British thermal unit (B.Th.U) : it is defined as the amount of heat required to raise the temperature of 1 pound (lb) of water by 1 ⁰F (degree Fahrenheit).

Calorific value can be expressed in two ways.

1.      Higher calorific value,

2.      Lower calorific value.