Engineering Chemistry S Datta

18
Fuels and Combustion
INTRODUCTION
Fuel is a combustible substance, which on combustion produces a large amount of heat, which
can be used for various domestic and industrial purposes. The fuels commonly used contain
carbon as the main constituent and some common fuels are wood, charcoal, kerosene, diesel,
producer gas etc. Fossil fuels are non-renewable energy resources which were stored up millions
of years ago by photosynthesis. The fossil fuels are coal, crude oil and natural gas.
The process of combustion involves oxidation of carbon, hydrogen etc. of the fuels to
CO 2
, H 2
O, and the difference in the energy of reactants and the products are liberated as large
amount of heat energy which is utilized.
Classification of fuels
Fuels
Natural
Derived
Solid Liquid Gaseous
Wood
Coal
Dung
Crude
oil
(Petroleum)
Natural
gas
Solid Liquid Gaseous
Coke
Charcoal
Petroleum coke
Coalbriquette
Tar
Kerosene
Diesel
Petrol
Fuel oil
LPG
Synthetic
gasoline
Coal gas
Water gas
Oil gas
Biogas
Coke oven
gas
Blast
furnace
gas
CALORIFIC VALUE
There are different expressions for calorific values:
(i) The quantity of heat evolved by the combustion of unit quantity of fuel is its gross
calorific value (GCV). Gross or higher calorific value is the quantity of heat liberated by
combusting unit mass of fuel in oxygen, the original material and the final product of combustion
being at a reference temperature of 25°C and the water obtained in the liquid state, represented
by GCV or HCV.
(ii) Net calorific value (NCV) is the quantity of heat evolved when a unit quantity of fuel
is burnt in oxygen, the original material and the final products of combustion being at a reference
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