Question

Name the unit in which calorific value of a fuel is expressed?

Answer 1

Hint: Calorific value may refer to the amount of heat generated after the complete combustion of a unit volume of a substance. Suppose that you were asked to boil a certain amount of water utilizing cow dung, LPG and coal as fuel. The amount of heat energy generated on complete combustion of 1 kg of a fuel is known as its calorific value.

Complete answer:
> Actually, the calorific value is considered to be the necessary parameter for representing the energy content of substances. The calorific value of a fuel is expressed in a unit called kilojoule per kg (kJ/kg). After understanding the concept of calorific value, let us write the chemical formula for calorific value as stated below:
Gross calorific value = Net calorific value + Latent heat of water vapours
> The efficiency or efficacy of fuel or food depends upon the calorific value. We can say that the efficiency is directly proportional to the calorific value. More the calorific value, more is the efficiency, and vice versa.
> It should also be noted that the water vapour produced in the combustion process also comprises heat. If this heat is recovered via distinct techniques, the material will possess higher gross calorific value. When any material in liquid form is given an energy, its phase changes from liquid to vapour. The absorbed energy in this process is known as heat of vaporization.
Calorific values of some fuels are depicted in Table below:

Fuel	Calorific value (kJ/kg)
Cow dung cake	6000-8000
Wood	17000-22000
Coal	25000-33000
Biogas	35000-40000
Kerosene	45000
Diesel	45000
Petrol	45000
CNG	50000
Methane	50000
LPG	55000
Hydrogen	150000

Note: Fuels having higher calorific value are considered to be good. If you look at the table, the suitability of fuels would be in the order like LPG, CNG, Petrol, Biogas, having lower to higher calorific value in the increasing order. Calorific value is an important parameter to define the commercial value of any material.