FuelsA Presentation on:

By Aashiq, Wasim, Uzair, Salahuddin, Bilal, Allauddin, Satish & Shravan.

FUELS Indroduction

Defination

Classification Of chemical Fuels

Characteristic of Fuels(Physical properties).

Various Uses of Fuels.

Introduction Fuels are all Those substance

Which on combustion give large Amount of heat.

IT contain carbon in main product. Combution Reaction =

The First fuels used By human is

WOOD

DEFINATION 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.

Classification Of Chemical Fuels

FUELS

Primary/Natural Secondary/Derived

LiquidEg Petroleum

Solide.g wood,caol

Gaseouse.g Natural gas

Gaseous e.g Coal gas

LiquidEg Alcohols

Solide.g Charcoal

Characteristic Of Chemical Fues

High Calorific value. Moderate Ignition

Temperature. Low Moisture Content. Low Non-Combustible Matter

Content.

Moderate velocity of combustion.

Product should not be Harmful.

Low cost.

Easy of Tranport.

Combustion Should be Easily Controllable.

USES 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.

USES 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.

Calorific value(GCV & NCV)

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.

Ignition TemperatureDefinition:

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:

oCarbon: 400°C

oGasoline: 260°C

oHydrogen: 580°C

oCarbon monoxide: 610°C

oMethane: 630°C

Unit Of Calorific Value• 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

High And Low Calorific Values

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.

Dulong FormulaAccording 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/gCalorific Value of H = 34500 cal/gCalorific 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

Solid Fuels

Introduction• 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.

• Transformation of coal in lignite to anthracite is known as metamorphism or progressive alteration in natural series.

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.

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:

Low rack coals are graded further on the basis of their moist B.T.U., indicating natural moisture

Meta-anthracite With minimum 92-98% fixed carbon and maximum 2-8% volatile matter.

Anthracite 87-91% fixed carbon, 9-13% volatile matter.

Semi-anthracite 86% fixed carbon, 14% volatile matter.

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.

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.

(I) Peat

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.

(II) Lignite

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.

(III) Bituminous Coals

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.

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. 

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.

Anthracite Coal

Liquid Fuels

• 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.

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:

Composition Of Petroleum

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%

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.

Mining of Petroleum

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.

REFINING OF

PETROLEUM

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.’

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.

(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.

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.

Fractionating tower

Portion of fractionating tower

Cracking of Heavy oils 

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

Definition

Types of Cracking

There are two methods of cracking

Thermal cracking

liquid phase or

vapour phase

Catalytic cracking

Fixed bed Moving bed

Thermal Cracking 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.

Sr. No. Characteristics Liquid Phase

Thermal CrackingVapour Phase

Thermal Cracking

1 Cracking temperature

Moderate (420-550°C) 600-650°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)

5 Pre-requirement for process

Any type of heavy oil can be used

Oil has to be vaporised readily

6 Time required Comparatively more Comparatively less

Comparison of liquid phase and vapour phase thermal cracking

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.

Fixed bed catalytic cracking

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

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.

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.

Moving/Fluidized Bed Catalytic Cracking

Sr. No. Characteristic Fixed bed catalytic

crackingMoving bed catalytic

cracking

1 Chamber reaction temperature 425°C-540°C 550°C-570°C

2 Pressure 1.5 kg/cm2 Around 1 kg/cm2

3 Octane value 80-85 85-90

Comparison of fixed bed and moving bed catalytic cracking

Advantages of Catalytic Process

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.

Sr. No.

Thermal Cracking Catalytic Cracking

1Heavy oils are cracked by simply

heating them under high temperature and pressure.

Heavy oils are cracked using small quantity of catalyst.

2It is of two types: Liquid and vapour

phase.It is of two types: Fixed bed and moving bed.

3

Temperature and Pressure is of high range as:

(a) Liquid Phase:T: 420-450°C, P: 15-100 kg/cm2

(b) Vapour Phase:T: 600-650°C, P: 15-20 kg/cm2

Temperature and pressure is of low range due to catalyst:(a) Fixed bed:

T: 425-540°C, P: 1.5 kg/cm2

(b) Moving bed:T: 550-570°C, P: very low

4Octane value of product ranges

from 60-80.Octane value of product ranges from 80-90.

5Yield % of gasoline is low (app. 50-

60%).Yield % of gasoline is low (app. > 75%).

6Efficiency is low and not commonly

used in refineries.Efficiency is high and used in modern

refineries.

7 Initial and operating cost is high. Initial cost is high but operating cost is low.

Comparison between thermal cracking and catalytic cracking

BIODIESEL

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 .

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

Method / Steps to obtain Biodiesel – A Green fuel

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.

Advantages of biodiesel

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.

CHEMICAL PROPELLANTS.

What is a Propellant?

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.

Chemical Propulsion

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.

Types of Propellant

Solid Propellant

s

Liquid Propellants

Hybrid Propellants

SOLID PROPELLANTS

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.

EXAMPLE OF SOLID PROPELLANT

The oxidizer is ammonium per chlorate (NH4ClO4) (69.93 %).

The fuel is a form of powdered aluminum (16 %).

CLASSIFICATION OF SOLID PROPELLANT

SOLID PROPELLANT

S

Homogeneous Solid Propellants

Simple Base Homogeneou

s Solid Propellants

Double Base Homogeneou

s Solid Propellants

Composite Solid

Propellants

Liquid PropellantsLiquid 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.

CLASSIFICATION OF LIQUID PROPELLANT

Liquid propellants used in launch vehicles can be classified into:

• Petroleum• Cryogenic propellants• Hypergolic propellants

Example of Liquid Propellant

Liquid oxygen and Liquid hydrogen

Cryogenic Propellants

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.

Hybrid Propellants

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 ).

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