What is Calorific value of fuel?

After a fuel is completely burned and the combustion products are cooled back to the initial temperature of the combustible mixture, the thermal energy released per unit volume of the fuel is known as the calorific value of fuel.The phrases calorific value and heat of combustion are both used to describe calorific value.

Almost all of he water vapour produced by the combustion process condenses when the combustion products are cooled to 25 °C. The high calorific value or gross calorific value of the fuel is the term used to describe the calorific value obtained in this way.

The heat that is released when the water vapour in the combustion products does not condense and remains as vapour is known as the reduced or net calorific value.