The document discusses various types of fuels including their definition, classification, properties, and uses. It describes solid fuels like wood, coal, and charcoal as well as liquid fuels derived from petroleum. The key solid fuel discussed is coal, which varies in composition and energy content depending on its rank as peat, lignite, bituminous coal, or anthracite. Liquid fuels mainly come from refining crude petroleum into products like gasoline, diesel, and jet fuel that are widely used for transportation and energy needs due to their high energy density.

2.  Indroduction
 Defination
 Classification Of chemical Fuels
 Characteristic of Fuels(Physical
properties).
 Various Uses of Fuels.

3.  Fuels are all Those substance Which on
combustion give large Amount of heat.
 IT contain carbon in main product.
 Combution Reaction =

4.  The First fuels
used By human is
WOOD

5.  Fuels are Define as “Substance which
Undergoes Combustion in the
presence of air to produce a large
amount of heat that can Be used
Economically For industrial and
Domestic PurPose”.
For E.g
 Wood,Coal,
 Kerosene,petrol,Diesel,Natural
gas(LPG)etc.

6. FUELS
Primary/Natural Secondary/Derived
Solid Gaseous Solid Gaseous
e.g wood,caol e.g Natural gas e.g Charcoal e.g Coal gas
Liquid
Liquid
Eg Alcohols
Eg Petroleum

7.  High Calorific value.
 ModerateIgnition
Temperature.
 Low Moisture Content.
 Low Non-Combustible Matter
Content.

8.  Moderate velocity of
combustion.
 Product should not be Harmful.
 Low cost.
 Easy of Tranport.
 Combustion Should be Easily
Controllable.

9.  Fuels play an important role in our
everyday life because they are used in
homes, transport and industry for
providing energy.
 Domestic Usage:
Fuels like wood, coal, kerosene, cow
dung etc are used.

10.  For Transport
Coal, diesel and petrol are used as fuel for
road, sea and air transport in automobiles
and locomotives.
 For industry:
Fuels like coal and natural gas are used.
 For Air Space Centre:
Specially prepared fuels like hydrazine
(Rocket fuels) [NH2-NH2] are used.

12. Definition:
“The number of units of heat evolved during complete
combustion of unit weight of the fuel” is called as calorific
value.
Calorific value can also defined as, “the number of
parts of water which gets heated through 1°C by the heat
evolved by the complete combustion of one unit weight fuel
under the conditions such as:
• Whole of heat evolved is absorbed by water
• The product formed leave the system at atmospheric
temperature & pressure.”
From both the above definitions, it is clear that a fuel, to be
most useful, must possess high calorific value because the heat
evolved by combustion of definite weight of fuel is directly
related/proportional to the calorific value of the fuel.

13. Definition:
Ignition temperature is defined as “minimum temperature to which a
substance must be heated before its burns spontaneously independent of the
source of heat.”
E.g.: Ethanol has an ignition temperature of 425 C/798 F and flash point of
12 C/54 F.
Each fuel should be brought above its Ignition Temperature for starting the
combustion process. The minimum ignition temperature at atmospheric pressure for
some substances are:
o Carbon: 400°C
o Gasoline: 260°C
o Hydrogen: 580°C
o Carbon monoxide: 610°C
o Methane: 630°C

14. • The calorific value of solid fuels is expressed as British Thermal Units per Pound (B.T.U. per
1b) or Kilogram Centigram Unit per Kilogram (K.C.U. per kg.).
• A British Thermal Unit may defined as, the heat required to raise the temperature of one
pound of water from 60 F to 61 F.
• Calorie, a unit of heat, may be defined as, the heat required to raise the temperature of one
kilogram of water from 15 C to 16 C.
Taking both above definitions of these units, a correlation between them can be written as;
1 B.T.U = 2.252 k.cals = 252 cals
1 k.cal = 1000 cals
1 k.cal = 3.968 B.T.U.
The calorific value can be also expressed as Centigrade Heat Unit (C.H.U.) which is the amount
of heat required to raise temperature of 1 pound water through one degree centigrade. Thus,
1 k.cal = 2.2 C.H.U = 3.968 B.T.U.
Also 1 k.cal/kg = 1.8 BTU/1b
1 k.cal/m3 = 0.1077 BTU/ft3
1 BTU/ft3 = 9.3 k.cals/m3

15. Calorific values are of two types :
1. High or Gross Calorific Value.
2. Low or Net Calorific Value.
• High Calorific Value is defined as “the total amount of heat
produced when one unit of the fuel has been burnt completely
and the products of combustion have been cooled to 16 C or
60 F.”
• Low Calorific Value is defined as “the net heat produced when
unit mass or volume of fuel is completely burnt and products
of combustion are allowed to escape into the atmosphere.”
The calorific value of fuels is determined theoretically by Dulong
formula or I.A. Davies formula.

16. According to Dulong, the calorific value of a fuel is the sum of the calorific
values of all the elements present . The calorific values of different elements
are given as under:
 Calorific Value of C = 8080 cal/g
 Calorific Value of H = 34500 cal/g
 Calorific Value of S = 2240 cal/g
Thus, Dulong’s Formula is given as:
H.C.V. (G.C.V.) = 1/100 [8080C + 34500 (H – O/8) + 2240S]
where C, H, O & S are the % of C, H, O & S respectively. In this formula,
oxygen is assumed to be present in combination with hydrogen as water;
and:
L.C.V. (N.C.V.) = H.C.V. – 0.09H X 587

18. • The solid fuels are available in nature (primary fuels) and also
prepared artificially know as (secondary fuels).
• The common natural solid fuels are wood, peat, lignite and
coal.
• The artificial solid fuels are charcoal, coal, briquettes.
• The other industrial fuels are fossil coals, oil shales, furnace slags,
peat, boiler slags, anthracite etc.
• Coal is a combustible solid fuel. By and large, all the solid fuels are
formed in nature from cellulose, lignin, proteins, resins, fats and
waxes.
• All these raw materials, which are formed under the earth y the
burials of partially decomposed vegetation, undergo
fermentation liberating CH4, CO2 and H2 gas and form peat,
which is slowly converted into lignite and then by further pressure
and heat, anthracite is formed.

20. A) Banded Coals
 This type of coal is a variety of bituminous or sub-bituminous coal.
 These are generally formed from peat.
 The structure of this type contains layers or bands of coal forming
materials.
B) Splint Coals
 This is also variety of bituminous of sub-bituminous coal, with dull
lustre and greyish-black colour.
 The bands of different coal forming materials are more irregular in
this variety, as a result it breaks with irregular rough fracture.
 There is no swelling on burning, but burns freely.
C) Cannal coals
 A variety of bituminous or sub-bituminous coal with compact fine
grained texture instead of bands.
 The colour varies from dark grey to black; possesses high volatile
matter, non-coking type, ignites easily and burns with luminous
smoky flame.

21. D) Bog-head coals
 A variety of bituminous or sub-bituminous coal similar to Cannel coal
in appearance as well as combustibility, but posses high content of
volatile matter and algal remains.
 When subjected to distillation it gives high yield of tar and oil.
E) High and Low rank coals
 High rank coals are further classified on basis of their percentage of
dry fixed carbon and volatile matter.
Example : Anthracite – There are three types of Anthracite:
With minimum 92-98% fixed carbon
Meta-anthracite
and maximum 2-8% volatile matter.
87-91% fixed carbon, 9-13% volatile
Anthracite
matter.
Semi-anthracite 86% fixed carbon, 14% volatile matter.
 Low rack coals are graded further on the basis of their moist B.T.U.,
indicating natural moisture

22. Coal :
 A mined sample of coal contains the coal substance, intermixed with
mineral constituents such as kaolin, shale, chloride, sulphides, etc.
The major constituents of coal are carbon, hydrogen and oxygen. The
properties of coal depend upon these constituents.
 There are hundreds of varieties of coal, depending upon its origin and
chemical constituents of coal. The important types of coal are peat,
lignite, bituminous and anthracite.
 The conversion of wood into coal takes place progressively.
Depending upon extent of transformation, coals are divided into 4
types (or grades or ranks):
During the progressive conversion from peat to anthracite, there is:
 Increase in - Carbon percentage, calorific value, density, lustre,
hardness, black colour intensity.
 Decrease in - Moisture, volatile matter, % of N, H, O, S & Ash.

23.  Peat is brown and fibrous in texture.
 Freshly mined out peat contains large quantity of water as it is found in water logged
areas.
 Air dried peat contains 15-25% moisture and it crumbles into powder during air
drying.
 Calorific value of peat is about 5400 cal/gm.
 It has low density.
 It contains 57% C, 6% H, 35% O & 3-6% ash.
Uses
 Peat type of coal gets powdered during combustion, therefore it is used after
briquetting, as domestic and industrial fuel.
 It is used for soil conditioning.
 It can be used for steam raising, thermal insulation, packing, gas purification and
some times for power generation.

24.  It is intermediate stage between peat and black coal.
 It is brownish black and more compact than peat.
 It contains 45-50% volatile matter and burns with long flame.
 It has Calorific value of 6000-6700 cal/gm.
 It cantains 65-70% C, 5% H, 20% O & 10-15% ash.
Uses
 After briquetting it is used as domestic and industrial fuel.
 Lignite is used for making ' producer gas ‘
 It can be used for power generation.

25. These coal burns with smoky yellow flame and are dark grey to black. They contains 70-
90% C and therefore they are classified as:
A) Sub-bituminous coal:
 This coal has characters between lignite and bituminous coal.
 It is harder and denser than lignite.
 It is grey black and has dull waxy lustre.
 It contains 70-75% C and large volatile matter upto 35-40%.
 It has Calorific value of 7000 cal/gm.
 It is non-caking coal.
Uses
 This coal is used for domestic and industrial purposes.

26. B)Bituminous coal:
 This coal has banded or laminated structure with alternate bright and dull layers.
 It has cubical fracture.
 It is black, dense and hard.
 It contains 75-80% carbon.
 It has Calorific value of 8000-8500 cal/gm.
Uses
 It is used most widely for domestic and industrial purposes.
 It is used for steam generation and power generation.

27. C) Semi-bituminous coal:
 It has characteristics between bituminous and anthracite.
 It has low volatile matter and 75-85% C.
 It has low caking property.
 It has Calorific value of 8400 cal/gm.
Uses
 Making of coke, high temperature heatings, coal gas for tar and chemicals.

28. This is highest rank or grade of coal.
 It has calorific value about 8700 cal/gm.
 It has 92-98% C.
 It contains very low volatile matter, ash and moisture.
 It is highly lustrous, black and hard coal.
Uses
 Being costly coal, it is used for specific industrial purposes.
 It is used as metallurgical fuel.
 It is used for making electrodes.
 It is used for high temperature heating.

30. • The liquid fuels are generally the products obtained from
petroleum refining.
• The main constituents of crude or raw petroleum are paraffin,
naphthalene and aromatic hydrocarbons. The concentration of
all there vary.
• The characteristic features of the liquid fuels are,
a) Liquid fuels possess low flash and fire point.
b) The calorific value of liquid fuels is generally very high.
c) The viscosity of liquid fuel is very low at ordinary
temperature.
d) The moisture and sulphur content of liquid fuels is low.

31. Crude Petroleum Oils
 Petroleum or crude oil is the main source of almost all liquid fuels used
now and a large number of petrochemicals such as plastics, rubbers, fibres,
organic chemicals, hydrogen etc. can be manufactured from crude oil
fraction.
 It has negligible percentage of ash and moisture and has minute quality of
Sulphur. It has very high calorific value such as 40,000 kJ/kg.
Origin of petroleum
 As per modern theory, petroleum is formed from buried debris of plants and
animals (organic matter), under favorable condition.
 The burial of the organic matter during volcano, upheavals in earth surface
should take place along with large quantity of water and under a dome of
hard, impervious rock.
 The anaerobic bacteria, higher temperature and radioactive substances
enables degradation of organic matter, in the presence of water, under the
dome, to form highly alkane rich matter as crude oil.
 The anaerobic bacteria take out oxygen atoms from cellulose, protein, oil
molecules and forms alkane rich crude oil.
For example:

32.  Petroleum, commonly known as rock oil or mineral
oil, is obtained from nature, under the earth, in the
form of deeply coloured highly viscous liquid.
 It contains a large number of different individual
chemicals ranging from methane to asphalt.
 Average elemental composition of crude petroleum is:
C = 80 to 87% H = 11 to 15%
S = 0.1 to 3% O = 0.1 to 0.9%
N = 0.4 to 0.9%

33. Petroleum contains following types of compounds:
 Open chain alkanes: Both straight chain and branched chain
alkanes are present in crude oil.
 Cycloalkanes: Crude oil contains cycloalkanes like cyclopentane,
cyclohexane and their alkyl substituted products.
 Aromatics: In all the crude oil benzene and alkyl substituted
benzenes are upto 2%.
 Asphaltenes: All the crude oils contain the small amount of
polycondensed aromatic solids as colloidal dispersion in crude oil.
 Resins: These are the polymeric substances. They are gummy and
are lower molecular weight polymers.

34. Petroleum gets formed collected under the earth. The depth of
such a storage of petroleum varies from few hundreds to few
thousands of feet below the surface of the earth.
It is surrounded by layers of natural gas, under the earth. In
short, the crude petroleum thus formed floats upon a layer of salt
water and is surrounded by layer of natural gas, deep below the
impervious rock. Mining of oil is done by drilling holes in
earth’s crust and sinking pipe up to the oil bearing rocks.
Due to the hydrostatic pressure exerted by natural gas,
surrounding to the stock of petroleum helps to get petroleum
piped out with pressure.

37.  Crude oil coming from the petroleum wells
consists of a viscous, dark coloured frothing
mixture of solid, liquid and gaseous
hydrocarbons containing sand and water in
suspension. In order to make it into a marketable
product, the oil is made free from impurities like
water, dissolved salts, sulphur etc.
 The process by which petroleum is made free
from impurities and separated into various useful
fraction having different boiling points and
further treated to remove undesirable
tendencies and to impart specific properties to
them is broadly called „REFINING OF PETROLIUM.‟

38. The Refining of Petroleum is done in the following stages:
(1) SEPARATION OF WATER (COTTRELL’S PROCESS)
The crude oil from the oil well is an extremely stable emulsion
of oil and salt 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 drop, which
separate out from the oil. To remove the persistent impurities, colour
etc., various fractions are passed over adsorbents like Kieselgure clay
etc. and the resultant oils are generally pure.
(2) REMOVAL OF HARMFUL IMPURITIES
NaCl and MgCl2 can corrode the refining equipment and can cause
scale formation in the heating pips. Hence special care should be
taken to remove them. Modern techniques of electrical desalting
and dehydration are developed for this purpose. Then oil is treated
with copper-oxide. The reaction occurs with sulphur compound,
which result in the formation of copper sulphide (a solid), which is
then removed by filtration.

39. (3) FRACTIONAL DISTILLATION
Fractional distillation is a combination of distillation
and rectification. Rectification process consists of counter
flow contacting of the vapour formed in distillation with the
liquid obtained by condensation of vapuor. For effective
rectification in distillation column, it is essential to see that
an ascending flow of vapour (formed due to the heat
supplied at the bottom section) meets the descending flow
of liquid (formed due to cold spraying in the top section).
These principles are used in the “FRACTIONTING TOWER”
widely used in petroleum refining.
Fractionating Tower (in figure) consists of a pipe still and
bubble tower. In pipe still the crude petroleum is heated
and is fractionated in bubble tower.

40. Bubble tower consists of horizontal stainless steel trays or plates at
short distances. Each tray is provided with a small chimney covered with
loose cap though which vapour rises up. These small chimneys are covered
with loose bubble caps.
Crude oil is piped through a pipe still where it is heated to about 400*C and
the vapours are the introduced near the bottom of the bubble tower. As the
vapour move upwards, the 3 higher boiling fractions condense at lower
plats and only the lower boiling fractions move to higher plates. The vapour
are allowed to pass up through higher plates via bubble caps. The heavier
component having high boiling fraction condense and the condensate
flows down to the next lower tray through the down comers. The vapour
which condenses give out the latent heat of condensation to the liquid in
the tray, from which more volatile components moves up the column.
This process of condensation and vapourization takes place many time
causing separation of the fractions according to their boiling points. Thus
higher boiling fractions condense at the lower parts of the column and lower
boiling fractions condense at the higher parts of the column. Thus the crude
oil is fractionated into different fractions depending on their boiling ranges
and are collected at different heights in the column. In this way mixture of
vapours and liquids of different boiling points are separated. This
fractionation gives uncondensed gases, gasoline, kerosene and gas oil
fraction.

41. Fractionating tower

42. Portion of fractionating
tower

44. Cracking is a process of converting heavy oil with
higher molecular weight hydrocarbons to the oil with lower
molecular weight hydrocarbon which is known as gasoline.
Thus, heavy oil is heated at a high temperature
under pressure or in the presence of catalyst to obtain
gasoline.
For example:
C10H22 C5H12 + C5H10
(Decane) n-Pentane Pentene

45. There are two methods of
cracking
Thermal cracking Catalytic cracking
liquid phase vapour
Fixed bed Moving bed
or phase

46.  Liquid phase thermal cracking:
By this method, any type of oil can be cracked. In this method, the
oil is pumped into the coil kept at 420°C-550°C under a pressure of
15-100 kg/cm2. As the temperature increases, a better quality of
gasoline is produced. The octane value of this gasoline is low, i.e. 65-
70. Therefore, it is mixed with higher octane value gasoline and then
used I engine.
 Vapour phase thermal cracking:
In this method, the heavy oil is heated in the heater at 400°C to
convert it into the vapours and then these vapous are passed to the
reaction chamber which is maintained at 600°C-650°C and under a
pressure of 10-20 kg/cm2. At this stage, the higher hydrocarbons are
converted into lower hydrocarbons easily and the octane value to
petrol is usually 75-80.

47. Comparison of liquid phase and vapour phase thermal cracking
Sr. Liquid Phase Thermal Vapour Phase
Characteristics
No. Cracking Thermal Cracking
Cracking Moderate (420-
1 600-650°C
temperature 550°C)
2 Pressure High (15-100 kg/cm2) Low (15-20 kg/cm2)
3 Yield percentages 50-60% -
4 Octane rating 65-70 >70 (75-80)
Pre-requirement for Any type of heavy oil Oil has to be
5
process can be used vaporised readily
6 Time required Comparatively more Comparatively less

48. Catalytic Cracking
Fixed bed catalytic cracking:
In this method, vapours of the heavy oil are heated in the presence of
catalyst due to which a better yield of petrol is obtained.
In this method, heavy oil is vaporised by heating in an electrical heater.
Then the vapours are passed over a series of trays containing catalyst. Generally, the
catalyst used are crystalline alumina-silicate, bentonite, bauxite and zeolites. The
reaction chamber is maintained at 425°C-540°C and under a pressure of 1.5 kg/cm2.
The cracked gases are taken out from the top of the reaction chamber (cracker) and
allowed to pass into fractionating tower, where gasoline fraction is collected. The
octane value of this gasoline is about 80-85. During the cracking, free carbon is also
formed which deposits on catalyst, then the flow of vapours of heavy oil is passed
over the second set of reaction chamber and the catalyst is earlier chamber is
regenerated by burning the carbon deposits with the help of air and reused.

49. Fixed bed catalytic cracking

50. Moving bed catalytic cracking:
It is also called fluidised bed catalytic cracking principle.
In this method, a fine powder of catalyst is circulated through
the cracker along with the vapours of heavy oil (higher hydrocarbon).
The catalyst accelerates and directs the cracking efficiently to form
gasoline and other lower hydrocarbons. For example:
C18H38 C10H22 + C8H16
n-octadecane n-decane Octene

51. Process:
In this method, a mixture of heavy oil and catalyst is heated
in the still to convert the heavy oil into vapours. There vapours
along with hot catalyst are brought to the cracker. The cracker is
maintained at a temperature of 550-570°C and atmospheric
pressure. In the cracker, the vapours of the heavy oil and hot
catalyst come in intimate contact with each other and the
breaking of higher molecular weight hydrocarbons into lower
hydrocarbon (Gasoline) takes place. The low boiling hydrocarbons
move up to the top of the cracker are passed through the cyclone
separator while the catalyst remains in the cracker.
These cracked gases are further passed through the
fractionating column to have three major fractions: Gasoline,
middle oil & heavy oil. The gasoline is further cooled and purified to
remove the impurities of sulphur, unsaturated hydrocarbons and
colouring matter, if present. The catalyst performs two functions: (1)
To get a better quality gasoline during cracking process & (2) to
carry heat during process.

52. Regeneration of exhausted catalyst:
Catalyst gets deactivated due to the
deposition of free carbon on catalyst. The
deactivated catalyst is taken from the bottom
of the cracker and brought into regenerator
where it is heated to about 500°C in the
presence of hot air to burn carbon dioxide
which is taken out from the top of the
generator. The regenerated catalyst in hot
condition is taken down to the vapours of heavy
oil and re-circulated in the cracker.

54. Comparison of fixed bed and moving bed catalytic cracking
Sr. Fixed bed catalytic Moving bed catalytic
Characteristic
No. cracking cracking
Chamber reaction
1 425°C-540°C 550°C-570°C
temperature
2 Pressure 1.5 kg/cm2 Around 1 kg/cm2
3 Octane value 80-85 85-90

55.  The cracking reaction can be carried out at lower temperature
and pressure.
 The cracking is specific in nature and can give proper quality
of gasoline.
 The octane value of gasoline is higher by catalytic process,
hence better for petrol engine.
 The process can be better controlled than the thermal process.
 The product contains less sulphur compounds.
 The percentage of gum or gum forming compounds is very
low.

56. Comparison between thermal cracking and catalytic cracking
Sr.
Thermal Cracking Catalytic Cracking
No.
Heavy oils are cracked by simply
Heavy oils are cracked using small quantity of
1 heating them under high
catalyst.
temperature and pressure.
It is of two types: Liquid and vapour
2 It is of two types: Fixed bed and moving bed.
phase.
Temperature and Pressure is of high Temperature and pressure is of low range due
range as: to catalyst:
(a) Liquid Phase: (a) Fixed bed:
3
T: 420-450°C, P: 15-100 kg/cm2 T: 425-540°C, P: 1.5 kg/cm2
(b) Vapour Phase: (b) Moving bed:
T: 600-650°C, P: 15-20 kg/cm2 T: 550-570°C, P: very low
Octane value of product ranges from
4 Octane value of product ranges from 80-90.
60-80.
Yield % of gasoline is low (app. 50-
5 Yield % of gasoline is low (app. > 75%).
60%).
Efficiency is low and not commonly
6 Efficiency is high and used in modern refineries.
used in refineries.
7 Initial and operating cost is high. Initial cost is high but operating cost is low.

58. Chemical nature:
 Chemically biodiesel is the methyl esters of
long chain carboxylic acids.
 Biodiesel is obtained by transesterification of
vegetable oil or animal fat with methyl
alcohol using sodium metal or sodium
methoxide, as catalyst .

59. Transesterificaion
Transesterificaion is the process of converting one ester to another
ester.
A molecule of oil or fat is the trimester of glycerol and three
molecules of long chain carboxylic acids. This triester is converted
into methyl ester of the fatty acids by the following reaction:
Vegetable oil/Animal fat

60. 1. Filter the cheap or waste vegetable oil/fat.
2. Heat it at 110ᵒC with stirring to remove any water from it.
3. Prepare sodium methoxide from sodium metal and methanol. Add the sodium
methoxide about 2% by weight to the vegetable oil or fat.
4. Add methanol about 20% stirring for 30 minutes.
5. Cool and mix sufficient water, stir well. The glycerol and soap dissolve in water
phase.
6. Separate the water insoluble phase (biodiesel) from water phase.
7. Add antioxidant to the biodiesel to avoid it to become gummy due to oxidation
and polymerization.
8. Biodiesel can be obtained from various vegetable oils like soyabeen oil, palm
oil, groundnut oil , cottonseed oil, mustard oil, sunflower oil etc.

61.  Biodiesel can be used as good fuel for diesel engines
but generally it is used as its 20% mixture with
diesel.
 Biodiesel is cheaper.
 It has high cetane numbers 46 to 54 and high C.V. of
about 40kJ/gm.
 It is regenerative and environment friendly.
 It does not give out particulate and CO pollutants.
 It has certain extent of lubricity.
 It is clean to use biodiesel in diesel engines.

63.  A propellant is a chemical which is used in the production of
energy and pressurized gas that is used to create movement
of a fluid or to generate propulsion of a vehicle or projectile
or other object.
 In rockets and aircraft, propellants are used to produce a gas
that can be directed through a nozzle, thereby producing
thrust. In rockets, rocket propellant produces an exhaust and
the exhausted material is usually expelled under pressure
through a nozzle. The pressure may be from a compressed
gas, or a gas produced by a chemical reaction. The exhaust
material may be a gas, liquid, plasma, or, before the
chemical reaction, a solid or liquid.

64.  In this method of propulsion techniques, propellants used are
basically chemicals, which produces high amount of energy
on burning. Depending upon the physical state of the
propellant used, they can be classified as:
 Propulsion using solid propellants: - Here solid propellants are
used to propel the rocket When the solid fuel is ignited, it
burns along the walls of the combustion chamber. As
discussed earlier, solid fuels have perforation. This is to
increase the surface area and eventually to increase the
thrust produced by the rocket. As the combustion proceeds,
the perforation shape changes into a circle. This provides
high thrust initially and thrust lowers during the middle of the
flight.

65. Types of Propellant
Solid Liquid Hybrid
Propellants Propellants Propellants

66. Any solid propellant consists of two parts:
• An oxidizer
• A fuel or a reducer.
In solid propellants, the fuel and oxidizer components are
prepared separately and are then mixed together. This is
because the oxidizer is in powder form and the fuel is a fluid of
varying consistency. They are then blended together and poured
into the rocket case under carefully controlled conditions. In
addition to fuel and oxidizer, some other compounds are added
to increase the efficiency of the propellants.

67.  The oxidizer is ammonium per chlorate
(NH4ClO4) (69.93 %).
 The fuel is a form of powdered aluminum
(16 %).

68. SOLID
PROPELLANTS
Homogeneous Composite Solid
Solid Propellants Propellants
Simple Base Double Base
Homogeneous Homogeneous
Solid Solid
Propellants Propellants

69. Liquid propellants are nothing but rocket propulsion fuels in liquid state.
They are made up of 2 parts:
• An oxidizer &
• A fuel.
Both the oxidizer and fuel are in liquid form. Liquid propellants are more
difficult to handle than solid propellants they require separate oxidizer
and fuel tanks. Lightweight pumps and injectors are used to spray the
propellants into the combustion chamber. The combustion of liquid
propellants can be controlled easily by controlling the rate at which the
pumps spray the liquid into the combustion chamber. Shutting off the
pumps completely can easily stop combustion. Thus controlling,
stopping and starting the combustion is very easy when liquid
propellants are used. In order to start the combustion process, spark
plugs, igniters, explosives are used.

70.  Liquid propellants used in launch vehicles
can be classified into:
• Petroleum
• Cryogenic propellants
• Hypergolic propellants

71.  Liquid oxygen and
 Liquid hydrogen

72. In a cryogenic propellant the fuel and the oxidizer are in the
form of very cold, liquefied gases. These liquefied gases are
referred to as super cooled as they stay in liquid form even
though they are at a temperature lower than the freezing
point. Thus we can say that super cooled gases used as liquid
fuels are called cryogenic fuels. These propellants are gases
at normal atmospheric conditions. But to store these
propellants aboard a rocket is a very difficult task as they
have very low densities. Hence extremely huge tanks will be
required to store the propellants. Thus by cooling and
compressing them into liquids, we can vastly increase their
density and make it possible to store them in large quantities
in smaller tanks. Normally the propellant combination used is
that of liquid oxygen and liquid hydrogen, Liquid oxygen
being the oxidizer and liquid hydrogen being the fuel. Liquid
oxygen boils at 297oF and liquid hydrogen boils at 423oF.

73.  Hybrid propellants are those propellants, which are a
mixture of solid and liquid propellants. In these propellants,
one of the two components (oxidizer and fuel) is solid
(usually fuel) whereas the other is liquid (usually oxidizer).
In a hybrid propellant rocket engine, the liquid part is
injected into the solid part. Thus the storage chamber of
the solid part acts as the combustion chamber. In a hybrid
rocket the oxidizer flows down the perforation (see solid
propellants) (This is not a part of the site tour) in the solid
fuel grain and reacts with the solid fuel. This produces the
hot exhaust gases required to produce thrust. This process
can be seen in the following image: In many hybrid motor
designs, the oxidizer is pressurized liquefied nitrous oxide
(N2O) while the fuel is cellulose (C6H10O5 ).