INTRODUCTION

A fuel can be defined as a combustible substance,
containing carbon as a main constituent, which on
proper burning gives large amount of heat, which can be
used economically for domestic & industrial purposes.

E.g.: wood, charcoal, coal, kerosene, petrol, diesel etc.

Fuel + O2 → Products + Heat
CLASSIFICATION OF FUEL
Fuels are classified as
 Primary fuels – Fuels which occur naturally
such as coal, crude petroleum and natural
gas. Coal and crude petroleum, formed from
organic matter many millions of years ago,
are referred to as fossil fuels.
 Secondary fuels – Fuels which are derived
from naturally occurring ones by a treatment
process such as coke, gasoline, coal gas etc.
CLASSIFICATION OF FUELS
FUEL
Primary Fuels
Solid
Eg. Wood,peat
Gas
Eg.Natural gas
Secondary fuels
Liquid
Eg.crude oil
Solid
EgCoke,charcoal
Gas
Eg.coal gas ,water gas
Liquid
Eg. Petrol ,LPG
CHARACTRISTICS OF A GOOD FUEL
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
High calorific value.
Moderate ignition temperature.
Low moisture content.
Low non-combustible matter content.
Moderate velocity of combustion.
Products of combustion.
Low cost.
Transportation.
Combustion should be easily controllable.
Efficiency.
CALORIFIC VALUE

The calorific value of a fuel is defined as the
quantity of heat (expressed in calories or kilo
calories) liberated by the complete combustion
of unit weight (1gm or 1kg) of the fuel in air or
oxygen, with subsequent cooling of the products
of combustion to the initial temperature of the
fuel.
Calorific value can be considered in a two ways:
1. Higher calorific value or Gross calorific value.
2. Lower calorific value or Net calorific value.

Higher calorific value or Gross calorific value.
The gross calorific value refers to the
heat evolved when the water produced
by combustion is condensed as a liquid.
 Thus the gross calorific value is the
quantity of heat liberated by the
complete combustion of unit weight of
the fuel with subsequent cooling of the
products of combustion to the initial
temperature of the fuel.

Lower calorific value or Net calorific value

The net calorific value gives the heat
liberated when water is in the form of
steam or water vapour
Under normal working conditions, water
vapours produced during combustion are
not condensed and escape as such along
with the hot gases
 Hence lesser amount of heat is available,
which is called Lower or net calorific value

Theoretical calculation of calorific
value of fuel
HCV = 1/100[8080 C + 34500 {H − O/8 }+2240
S]kcal/kg
LCV= [GCV-9H/100 x 587]
=[GCV-0.09 x 587] kcal/kg
where C, H, O, S refer to % of carbon,
hydrogen, oxygen and sulphur respectively.
Latent heat of steam=587kcal/kg
Analysis Of Coal And Its Significance
The composition of coal varies widely according to
source & age. hence its analysis is necessary to
interpret the results from the point of view of
classification, price fixation and industrial
utilization of coal.
In order to determine the quality of coal, it is
subjected to the following two types of analysis:
1. Proximate analysis,
2. Ultimate analysis
Proximate analysis of coal
• Determines only fixed carbon, volatile matter,
moisture and ash
• Useful to find out heating value (GCV)
• Simple analysis equipment
Ultimate analysis of coal
• Determines all coal component elements: carbon,
hydrogen, oxygen, sulphur, other
• Useful for furnace design
• Laboratory analysis
Proximate analysis
Moisture content
• % of moisture in fuel (0.5 – 10%)
• Reduces heating value of fuel
• Weight loss from heated and then cooled powdered
raw coal
Volatile matter
• Methane, hydrocarbons, hydrogen, CO, other
• Typically 25-35%
• Easy ignition with high volatile matter
• Weight loss from heated then cooled crushed coal
Ash
• Impurity that will not burn (5-40%)
• Important for design of furnace
• Ash = residue after combustion
Fixed carbon
• Fixed carbon = 100 – (moisture + volatile matter +
ash)
• Carbon + hydrogen, oxygen, sulphur, nitrogen
residues
• Heat generator during combustion
Ultimate Analysis

Determination of carbon &hydrogen
Significance:
Higher the %of carbon , greater is the calorific
value & better is the quality of coal.
Lesser the % of hydrogen better is the quality of
coal.
% of C = increase in weight of KOH tube x 12 x
100
weight of coal taken x 44
% of H = increase in weight of CaCl2 tube x 2 x
100
weight of coal taken x 18
Determination of Nitrogen
Significance:
Nitrogen is inert and incombustible gas &does
not contribute any useful property.
% of N = volume of acid used x Normality x
1.4
Weight of coal taken
Determination of Sulphur
Coal is burnt in a bomb calorimeter in a current of
oxygen. During burning sulphur present in coal
is oxidized & converted in to sulphate. The ash
formed is now extracted with dilute hydrochloric
acid and the acid extract is heated with barium
chloride solution to give a white precipitate of
barium sulphate which is filtered , washed, dried
and weighed.
S→ SO2 →BaSO4
Significance:
Sulphur present in coal is harmful for use.
oxidation products of sulphur have corrosive
effect. hence the presence of sulphur in coal is
undesirable.
% of S = 32 x weight of BaSO4 x 100
233 x weight of coal
Liquid Fuels
Petroleum (mineral oil)
Petroleum is a natural product generated
from organic material by physical &
chemical process inside the earth.
Carbon
:79.5 to 87.1%
Hydrogen
: 11.5 to 14.8%
Nitrogen + Oxygen : 0.1 to 0.5%
Sulphur
: 0.1 to 3.5%
Mining of Petroleum
Refining of Petroleum
Separation of water: The process of
removing oil from water consists in
allowing the crude to flow between two
highly charged electrodes. The colloidal
water droplets aggregates to form large
drops, which separate out from oil.
2) Removal of harmful impurities: Electrical
desalting and dehydration can be used.
3) Fractional distillation: It is a combination of
distillation and rectification.
1)
Cracking

The process of composition of less volatile higher
hydrocarbon molecules into more volatile simple
hydrocarbon of lower molecular weight by the application
of heat and catalyst is known as cracking.
During the cracking process changes occurs as follows:
1. Size of molecules decreases & volatility increases.
2. A mixture of lower molecular weight hydrocarbon having
lower boiling point will be formed.
3. Cyclisation may occur.
4. Straight chain hydrocarbon converted into branched
chain hydrocarbon.
 Types
of cracking :
Thermal
cracking
Catalytic
cracking
Liquid phase
thermal cracking
Fixed bed
catalytic cracking
Vapour phase
thermal
cracking
Moving bed
catalytic cracking
Thermal Cracking
Liquid phase thermal cracking: heavy oil is
cracked at 475 -530˚C and pressure of
100Kg/cm2 . The yield is 50-60% & octane
rating of the petrol is 65-70 .
b) vapour phase thermal cracking: oil is first
vaporized & then cracked at about 600650˚C &under a low pressure of 1020Kg/cm2 . This process is suitable for
those oils which may be readily vaporized.
It has poor stability than petrol.
a)
Catalytic cracking
Moving bed catalytic cracking
Gasoline or petrol
Gasoline is the most important liquid fuel
derived from petroleum and is obtained
between 40-120ºC.
 It is a mixture of hydrocarbon such as C5
H12 to C8H18.
 Its approximate composition is C = 84%
H = 15%
N+S+O = 1%
 Its calorific value is 11250 kcal/kg.

Refining of gasoline
Gasoline contains some undesirable
straight chain hydrocarbons & sulphur
compounds. And it has to be refined by
chemical treatment.
Treatment with sulphuric acid:
2. Removal of sulphur compounds:
3. Stabilization of gasoline:
4. Addition of inhibitors
1.
Characteristics of an ideal gasoline :
It must be a cheap and readily available.
2) It must burn clean &produce no
corrosion.
3) It must have high calorific value.
4) It must be knock resistant.
5) It should mix readily with air.
1)
Knocking

Knocking is a term related to the internal
combustion engine working on petrol.
Tendency to knock depend on:
fuel air ratio,
Design of engine,
Speed of engine
Shape of piston,
location of spark plug & also upon running
conditions.
o Knocking results in the loss of efficiency of
engine, causing fuel wastage and
increased wear & tear of engine.
o Straight chain>branched chain>olefins
paraffins > cyclo paraffins >aromatic
sparaffins






Octane value


It expresses the knocking characteristics of a petrol.
It is defined as the percentage by volume of isooctane in a mixture of iso-octane and n-heptane
which matches the knocking characteristics of fuel.
n-heptane
iso-octane
(C7H16)
(C8H18)
knocks the most
knocks the least
poor anti-knock property good anti-knock property
Octane no= 0
Octane no = 100
The octane number can be increased by
addition of tetramethyl lead or diethyl
ether.
 Oils having high octane number has a
low cetane number.

Hydrocarbon
Octane Number
Benzene
110
Toluene
104
Cyclopentane
82
Cyclohexane
77
butene
80
Cetane number


In a diesel engine , the fuel is exploded not by a
spark, but by the application of heat & pressure.
The knocking characteristics of a diesel is expressed
in terms of a cetane number.
n- hexadecane
C16H34
knocks the least
(least ignition delay)
Cetane no = 100
2- methyl naphthalene
C11H10
knocks the most
(higher ignition delay)
Cetane no = 0
The cetane number can be increased by
addition of ethyl nitrite, ethyl nitrate.
 Oils having high cetane number has a
low octane number.

Compounds
cetane Number
Heptane
56
Octane
64
Decane
77
Dodecane
88
tetradecane
96
Types of deisel
engine
Speed in r.p.m
Diesel oil used
having cetane
number
Uses
Low speed
100-150
Heavy oil having
cetane no.25
Ships
Medium speed
500-1500
Medium oils having
cetane no. 25-30
Tractors
High speed
1500-2000
Light oils having
cetane no. 45-50
Buses, trucks
Power alcohol
It is used in internal combustion engine.
It is not used as a prime fuel but only as an
additive to motor fuels.
 Calorific value of 7000kcal/kg.
 Octane number is 90.
Advantages
i. On adding it increses the octane no of
petrol.
ii. Have lesser starting difficulties.
iii. Absorbs traces of moisture.


Bio-diesel
Chemically biodiesel is the methyl esters
of long chain carboxylic acids.
 It is obtained from vegetable oil by the
process transesterification.
 A molecule of oil is the triester of
glycerol and three molecules of long
chain carboxylic acids.this triester is
converted into methyl esters of the fatty
acids

Advantages of bio-diesel
i. It is cheaper
ii. Has high cetane number& high calorific
value.
iii. Regenerative & environment friendly.
iv. Has lubricity.
v. It does not give particulate and CO
pollutants.
vi. It is clen to use in diesel engine
vii. Provides good market to vegetable oils
& reduces our dependence for diesel on
foreign countries.
Propellants
An oxygen rich substance undergoes
combustion in a definite & controlled
manner, evolving a huge volume of gases
 It used in rockets, hence called as “ Rocket
Propellants”.

Two types of propellants
1. Solid propellants.
2. Liquid propellants.


1.
2.
3.
4.
5.
6.
Characteristics of a good propellant
Should undergo combustion to produce
low molecular weight products.
Should undergo combust steadily.
Should have low ignition delay.
Should have high density.
Should be stable at variable
temperature.
Should be safe to transport.
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