FUEL

1. Fuels
Fuel is any material that stores Energy that
can later be extracted to perform mechanical
work in a controlled manner.
Most Fuels produce Energy by various other
exothermic chemical reactions and nuclear
reactions.
Most common household fuels contain the
element Carbon.
Fuels that contain carbon and hydrogen only are
called Hydrocarbons. Few traces of sulphur are
also present in it.

2. Types of Fuel
There are mainly two types of fuel,
1.Chemical Fuel.
2.Nuclear Fuel.
Chemical Fuel: Chemical fuels are substances that
release energy by reacting with substances
around them, most notably by the process of
oxidation or burning.
A good fuel releases it’s energy over a longer period
of time.
Another word for burning is Combustion ie. we
combine the element with Oxygen gas.

3. Chemical Fuel
Chemical Fuels can be of two types,
1.Biofuels: Biofuel can be broadly defined as
solid, liquid, or gas fuel consisting of, or
derived from biomass. Biomass can also be
used directly for heating or power—known as
biomass fuel. Biofuel can be produced from
any carbon source that can be replenished
rapidly e.g. plants. Many different plants and
plant-derived materials are used for biofuel
manufacture.
Example: Bio alcohol, biodiesel, wood etc.

4. Chemical fuel
2.Fossil Fuels: Fossil Fuels are formed from Living
things millions of years ago. They are Hydrocarbons
and are Finite Fuels ie. They will run out in the future
and cannot be regenerated. There are three main
Fossil Fuels:
Coal, Oil and GasCoal, Oil and Gas
Oil: This was
formed by dead
sea creatures
falling to the sea-
bed where they
were subjected to
chemical change
by Bacteria.
Coal: This was
formed by the
decay of Vegetation
which was
subjected to heat
and pressure over
a very long period
of time.
Gas was formed
in much the
same way as Oil.
It is often
collected when
drilling for Oil.

5. Classification of Fuel
Fuels may be classified into the following
general terms:
1.Solid Fuel
2.Liquid Fuels
3.Gaseous Fuel
Each of these fuels may be subdivided into the
following categories-
1.Natural Fuels
2.Prepared Fuels

6. Solid Fuel
Wood: At one time it was an extensively used
fuel. It consists of mainly carbon and
hydrogen.
Peat: It is a spongy humid substance and
contains about 30% water. It has to be dried
before use. It is the first stage in the formation
of coal.
Lignite or brown coal: It is the next stage of
peat in the coal formation and an intermediate
variety between bituminous coal and peat. It
contains nearly 40% moisture and 60% of
carbon.

7. Solid Fuel
Bituminous Coal: It represents the next stage
of lignite in the coal formation and contains
very little moisture(4-6%) and 75 to 90% of
carbon.
Anthracite Coal: It represents the final stage
of coal formation and contains 90% or more
carbon.

8. Solid Fuel

9. Solid Fuel
Wood Charcoal: It is made by heating wood
with a limited supply of air to a temperature
not less than 280˚C.
Briquetted Coal: It is produced from finely ground
coal by moulding under pressure with or without a
binding material.
Pulverised Coal: The low grade coal with high ash
content is powdered to produce pulverised coal.

10. Liquid Fuels
Almost all the commercial liquid fuels are derived
from natural petroleum. The liquid fuels consist of
hydrocarbons.
The natural petroleum may be separated into
petrol or gasoline, paraffin oil or kerosene, fuel
oils and lubricating oil by boiling the crude oil at
different temperature and subsequent fractional
distillation.
The following liquid fuels are important from the
subjects point of view.
1.Petrol or gasoline: It is the lightest and most
volatile liquid fuel, mainly used for light petrol
engines. It is distilled at a temperature from 65˚-
220˚C.

11. Liquid Fuels
2.Kerosene or Paraffin oil: It is the heavier and
less volatile fuel than the petrol, and is used
as heating and lighting fuel. It is distilled from
220˚-345˚C.
3.Heavy Fuel oil: The liquid fuels distilled after
petrol and kerosene are known as heavy fuel
oil. These oils are used in diesel engines and
oil fired boilers. They are distilled at a
temperature from 345˚-470˚C.

12. Merits and Demerits of Liquid Fuel
over Solid Fuel
Following are the merits and demerits of liquid fuels
over Solid Fuel:
Merits:
1.Higher Calorific value.
2.Lower storage capacity required.
3.Better economy in handling.
4.Better control of consumption by using valves.
5.Practically no ashes.
6.Non-deterioration in storage.
7.Non-corrosion of boiler plants.
8.Higher efficiency.

13. Merits and Demerits of Liquid Fuel
over Solid Fuel
Demerits:
1.Higher cost
2.Greater risk of fire.
3.Costly containers are required for storage and
transport.

14. Gaseous Fuel
The natural gas is, usually found in or near the
petroleum fields, under the earth’s surface. It
essentially consists of marsh gas or methane(CH4)
together with small amounts of other gases such
as ethane(C2H6), carbon dioxide(CO2).
The following gaseous fuels are important from
subject point of view.
1.Coal gas: It is obtained by carbonization of coal
and consists mainly of H
2,CO and various
hydrocarbons.
2.Producer Gas: It is obtained by the partial
combustion of coal, coke, anthracite coal or
charcoal in a mixed air-steam blast.

15. Gaseous Fuel
Water gas: It is a mixture of H2 and CO and is
made by passing steam over incandescent
coke.
Mond Gas: It is produced by passing air and a
large amount of steam over waste coal at
about 650C.
Blast Furnace Gas: It is a by-product in the
production of pig iron in the blast furnace.
Coke oven gas: It is by-product from coke
oven and is obtained by the carbonization of
bituminous coal.

16. Merits and Demerits of Gaseous
Fuel:
Merits:
1.The supply of fuel gas and hence the temperature
of furnace is easily and accurately controlled.
2.The high temperature is obtained at a moderate
cost by pre-heating gas and air with heat of waste
gases of combustion.
3.They are directly used in internal combustion
engine.
4.They do not produce ash or smoke.
5.They undergo complete combustion with minimum
air supply.

17. Merits and Demerits of Gaseous
Fuel
Demerits:
1.They are readily inflammable.
2.They require large storage capacity.

18. Requirements of Good Fuel
1.A good fuel should have low ignition point.
2.It should have a high calorific value.
3.It should freely burn with a high efficiency,
one it is ignited.
4.It should not produce harmful gases.
5.It should produce least quality of smoke and
gases.
6.It should be economical, easy to store and
convenient for transportation.

19. Calorific value of Fuels
The calorific value of fuel or heat value of a
solid or liquid fuel may be defined as the
amount of heat given by the complete
combustion of 1 kg of fuel. It is expressed in
terms of kJ/kg of fuel. The calorific value of
gaseous fuel is expressed in terms of kJ/m³.
Fuel+O2=CO2+H2O+heat
Following are the two types of calorific values:
1.Gross or higher Calorific Value.
2.Net or Lower Calorific Value.

20. Gross or Higher Calorific Value
The amount of heat obtained by the complete
combustion of 1kg of a fuel, when the products
of its combustion are cooled down to the
temperature of the supplied air, is called gross
or higher calorific value of fuel.
Fuel+O
2
=CO
2
+H
2
O+SO
2
+heat+flue gas
H
2
O+heat= Steam
If heat taken away from the steam and hot flue
gas is recovered then the amount of heat
produced per kg is known as gross or higher
calorific value.

21. Net or Lower Calorific Value
When the heat absorbed or carried away by
the product of combustion is not recovered,
and the steam formed during combustion is
not condensed, then the amount of heat
obtained per kg of fuel is known as net or
Lower Calorific Value.
If the HCV is known then the LCV may be
obtained by subtracting the amount of heat
carried away by the products of
combustion(especially steam).
LCV=HCV-heat of steam formed during
combustion.

22. Dulong’s Formula
If the chemical analysis of a fuel is available
,then the higher calorific value of fuel is
determined by the following formula called
Dulong’s formula:
HCV=33800C+144000H
2+9270S kJ/kg
Where C, H
2
and

S represent the mass of
Carbon, Hydrogen and Sulphur in 1 kg of fuel,
and the numerical values indicate their
respective calorific values.