Question

Define the characterstics of fuel

Answer 1

Fuels are any material that store potential energy in forms, which upon burning in oxygen liberates heat energy.
Calorific value of fuel is the total quantity of heat liberated when a unit mass or volume of fuel is completely burnt.
Higher or gross calorific value (HCV) in the total amount of heat produced when a unit mass/volume of fuel has been burnt completely and the products of combustion have been cooled to room temperature (15°C or 60°F).
Lower or net calorific value (LCV) is the heat produced when unit mass (volume) of the fuel is burnt completely and the products  are permitted to escape.

Answer 2

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Any substance which when undergo chemical or nuclear change to produce energy and which can be converted into useful work is known as fuel. Calorific value of a fuel is defined as the amount of energy released when unit mass of the substance(fuel) undergoes complete combustion.