fuels and lubricants.pdf

Unit II Fuels and Lubricants
1
diesel coal
LPG
plastic Waste of plastic

Fuels
Fuel is a combustible substance which on proper burning gives large
amount of heat, which can be used economically for domestic and
Industrial purposes. Examples are wood, coal, petrol
Fuel + O2 Products + heat
Reference Jain and Jain, 16th edition Page 55 2

Classification of fuels

Peat (decomposed vegetable matter ) Lignite (brown coal)
Natural gas Coke
4

Characteristics of Good Fuel
 Suitability: The fuel selected should be most suitable for the process. E.g.,
coke made out of bituminous coal is most suitable for blast furnace.
 High Calorific value
 Ignition Temperature: A good fuel should have moderate ignition
temperature.
 Moisture content: Should be low
 Non combustible matter content
 Velocity of combustion: It should be moderate
 Nature of the products
 Cost of fuel, Smoke, Control of the process

the amount of energy required to warm one gram of
air-free water from 15 to 16 °C at standard atmospheric
pressure. Experimental values of this calorie ranged from
4.1852 J to 4.1858 J.
Fuels and Combustion
Calorie:
Kilocalorie: is equal to 1000 calories. This is the amount of
energy required to warm one kilogram of air-free water from 15
to 16 °C at standard atmospheric pressure..
Units of heat
6

British Thermal Unit: the amount of heat required to raise the
temperature of one pound (0.45359237 kilograms) of water
through one degree Fahrenheit (60-61 °F). Experimental values of
1 B.Th.U.=252cal
Centigrade heat unit (C.H.U.) the amount of heat required to
raise the temperature of one pound of water through one
degree centigrade. 1Kcal=3.968B.Th.U=2.2C.H.U.
Units of heat
7

CH4 + 2O2 CO2 + 2H2O
steam
is the total amount of energy produced,
when unit mass/volume of the fuel has been burnt completely, and
the products of combustion have been cooled to room
temperature (15 ⁰C)
Higher or gross calorific value:
Reference Jain and Jain, 16th edition Page 56
Cooled to 15 ⁰C and more energy
is released in the process
8

is the net heat produced, when
unit mass/volume of the fuel has been burnt completely and the
products of combustion are permitted to escape.
LCV=HCV – Latent heat of water formed
=HCV – mass of hydrogen x 9 x Latent heat of steam
Latent heat of steam at room temperature is 587kcal/Kg
Lower or net calorific value (LCV):
CH4 + 2O2 CO2 + 2H2O
steam
9

Bomb Calorimeter
10
O2 pressure is 25atm

11
• Flame temperatures of magnesium and magnesium alloys can
reach 3,100 °C (5,610 °F)
• Beckmann thermometer can estimate temperature changes to
0.01 °C

Mass of fuel = x gm
HCV of the fuel = L cal/gm
Heat liberated by burning of x gm of fuel = xL cal (1)
Mass of water in calorimeter = W gm
Water equivalent of the calorimeter in gram = w
Initial temperature of water in calorimeter = t1
Final temperature of water in calorimeter = t2
Heat absorbed by water and apparatus = (W+w)(t2-t1) (2)
xL = (W+w)(t2-t1) from (1) and (2)
Bomb Calorimeter
L= (W+w)(t2-t1)/x cal/gm
12

LCV = L – 0.09H*587 cal/gm
Corrections
a) Fuse wire correction
b) Acid correction, tA
c) Cooling Correction, tC
d) Cotton thread correction, tT
(W+w)(t2-t1)
x
HCV or L= cal/g
(W+w)(t2-t1+tC)-[tA+tF+tT]
x
L= cal/g
Bomb Calorimeter
13

In a reaction the quantity of heat
that raises the temperature of some substance/body by some amount,
the same quantity of heat can simultaneously raise the same
temperature of a certain mass of water. The mass of water is then
termed as water equivalent.
The amount of water which has the same heat capacity as that of the
body/substance.
body
q
t
t
Water Equivalent of Calorimeter:
Bomb Calorimeter
14

Dulong’s formula
Theoretical calculations of calorific value
where C, H, O, S refer to % of carbon, hydrogen, oxygen and
sulphur respectively.
1
100
8080*C + 34500(H- ) + 2240*S
O
8
HCV = Kcal/kg
LCV= HCV – 0.09*H*587 , kcal/kg
15

Numerical 1
Calculate the gross and net calorific values of coal having the following
Compositions Carbon=85%, Hydrogen=8%, Nitrogen=2%, ash=4%,
Sulphur= 1%, Latent heat of steam=587cal/g
1
100
8080*C + 34500(H - ) + 2240*S
O
8
GCV or HCV = Kcal/kg
1
100
8080*85 + 34500(8 - ) + 2240*1
0
8
HCV = Kcal/kg
HCV = 9650.4 kcal/kg
NCV = HCV- 0.09*H*587 kcal/kg
= 9650.4 - 0.09*8*587
= 9227.8 kcal/kg

Numerical 2
0.72g of a fuel containing 80% carbon, when burnt in bomb calorimeter,
increased the temperature of water from 27.3 to 29.1 ⁰C. if the calorimeter
Contains 250g of water and its water equivalent is 150g, calculate the HCV
of the fuel. Give your answer in kJ/Kg.
X=0.72g, W=250g, w=150g, t2=29.1 ⁰ C, t1=27.3 ⁰C
(W+w)(t2-t1)
x
L= cal/g
(250+150)(29.1-27.3)
0.72
HCV= cal/g
HCV= 1000*4.2 J/g or kJ/kg
=4200 kJ/kg

Coal
Coal is a highly carbonaceous matter that has been formed as a
result of alteration of vegetable matter (e.g. plants) under certain
favorable conditions. It is chiefly composed of C, H, N and O,
besides non-combustible inorganic matter

Cellulose
lignin
Constituents of wood
19

Classification of Coal
Various types of coal commonly recognized on the basis of rank
Or degree of alteration or coalification from the parent material,
wood are:
Wood Peat Lignite Bituminous coal Anthracite
This progressive transformation of wood to anthracite results in
1. Decrease in moisture content
2. Decrease in H, N, O, and S content with a corresponding increase in C content
3. Decrease in volatile content
4. Increase in calorific value
5. Increase in hardness 20

1. Peat: is a fibrous jelly like mass. It is regarded as the first stage in the
coalification of wood. It is uneconomical fuel, It may contain as much
as 80-90% of water but on air-drying , it burns freely. Its calorific value
is about 5400kcal/kg (on air-dry basis).
2. Lignite (brown coal): are soft brown colored variety of lowest rank coal
which consists of vegetable matter decomposed more that in peat
Lignite is compact in texture, containing 20-60% moisture and on
air-drying, it breaks up into small pieces. The calorific value is about
6500-7100 kcal/kg
21

3. Bituminous coal: are pitch-black to dark-grey coals, which usually
soil hands. They show a laminated structure of alternate very bright
and dull layers. Its calorific value on ash-free basis is about
8000-8500Kcal/kg.
4. Anthracite: is the highest rank coal, containing highest percentage of
carbon (92-98%) and has the lowest volatile matter and moisture
contents. They are hardest of all kinds of coals, quite dense and
lustrous in appearance. The calorific value is about is about
8600-8700 Kcal/kg 22

1. Proximate analysis parameters include moisture, volatile matter,
ash, and fixed carbon. It provides valuable information in assessing
the quality of coal.
Coal analysis
2. Ultimate analysis which is more comprehensive, is dependent on
quantitative analysis of various elements present in the coal sample,
such as carbon, hydrogen, sulfur, oxygen, and nitrogen

1.1 Moisture is an important property of coal, as all coals are
mined wet. Groundwater and other extraneous moisture is
known as adventitious moisture and is readily evaporated.
Moisture held within the coal itself is known as inherent
moisture and is analyzed quantitatively.
Percentage of moisture =
Loss in weight
Weight of coal taken
* 100 (1)
1. Proximate analysis
1g of finely powdered air-dried coal sample is taken in a crucible
and heated for 1hour inside a hot air oven maintained at 105- 110⁰C.
The sample is then cooled in a desiccator and weighed. Loss in weight
is reported as moisture

1.2 Volatile matter in coal refers to the components of coal,
except for moisture, which are liberated at high temperature in
the absence of air. This is usually a mixture of short and long
chain hydrocarbons, aromatic hydrocarbons and some sulfur
The dried sample of coal in (1) is then covered with a lid and placed
in an electric furnace (muffle furnace) , maintained at 925 ± 20 ⁰C. the
crucible is then taken out of the oven after 7 minutes of heating. The
crucible is first cooled in air then in desiccator and loss of weight is
measured
% of volatile matter =
Loss in weight due to removal of volatile matter *100
(2)
25

1.3 Ash content of coal is the non-combustible residue left
after coal is burnt. It represents the bulk mineral matter after
carbon, oxygen, sulfur and water (including from clays) has
been driven off during combustion.
The residual coal in the crucible (2) is then heated without a lid in a
muffle furnace at 700±50 ⁰C for 30 minutes. The crucible is taken
out cooled in air first, then in desiccator and weighed. Heating,
cooling and weighing is repeated till a constant weight is obtained.
Percentage of ash =
weight of ash left
* 100

1.4 Fixed carbon: The fixed carbon content of the coal is the
carbon found in the material which is left after volatile
materials are driven off. This differs from the ultimate carbon
content of the coal because some carbon is lost in
hydrocarbons with the volatiles. Fixed carbon is used as an
estimate of the amount of coke that will be yielded from a
sample of coal. Fixed carbon is determined by removing the
mass of volatiles determined by the volatility test, above, from
the original mass of the coal sample.
Fixed carbon = 100 – % of (moisture + volatile matter + ash)

Importance of proximate analysis
1.1 Moisture:
lowers the effective calorific value of the coal
Quenches the fire in furnace
Increase the transportation charges
1.2 Volatile matter:
Large proportion of volatile matter escapes without burning
Decreases the calorific value
Increases the flame size
1.3 Ash:
Useless, non combustible matter which reduces the calorific value of coal
Causes hindrance to flow of air and heat, therby lowering the temperature
It forms clinker, which block the interspaces of the grate.
Increases the transportation charges
Wear of furnace walls and burning apparatus
1.4 Fixed carbon: Higher the percentage of fixed carbon, greater is its calorific
value and better the quality of coal.

2. Ultimate analysis
It involves the analysis of C, H, N, S, O and ash
2.1 Carbon and Hydrogen:.
Fig. Estimation of carbon and hydrogen

It involves the analysis of C, H, N, S, O and ash
2.1 Carbon and Hydrogen: about 1-2g of accurately weighed coal sample
is burnt in a current of oxygen in a combustion apparatus. C and H of
the coal are converted CO2 and H2O respectively. The gaseous
products of combustion are absorbed respectively in KOH and CaCl2
tubes of known weights. The increase in weights is measured and
percentage of C and H is determined.
Percentage of C =
increase in weight of KOH tube * 12 * 100
Weight of coal sample taken * 44
C + O2 CO2
12 44
2KOH + CO2 K2CO3 + H2O
30

Percentage of H =
increase in weight of CaCl2 tube * 2 * 100
weight of coal sample taken * 18
2.1 Hydrogen
H2 + ½ O2 H2O
CaCl2 + 7H2O CaCl2.7H2O
31

2.2 Nitrogen:
Fig. Estimation of nitrogen by Kjeldahl’s method

2.2 Nitrogen: About 1g of accurately weighed powdered coal is heated
with concentrated H2SO4 along with K2SO4 (catalyst)in a long necked
flask (called Kjeldahl’s flask). After the solution becomes clear, it is
treated with excess KOH and the liberated ammonia is distilled over
and absorbed in a known volume of standard acid solution. The
unused acid is then determined by back titration with standard acid
solution. The consumed acid is related to N in coal as follows
Percentage of N =
Volume of the acid used(ml) * Normality * 1.4
weight of coal sample taken

34
Step1.
The sample is first digested in strong sulphuric acid in the presence
of catalyst
1. Nitrogenous organic compound + concH2SO4 (NH4)2SO4
2. (NH4)2SO4 + 2NaOH 2NH3 + Na2SO4 + 2H2O
3. NH3 + HCl NH4Cl + HCl (left back)

Ultimate analysis
2.3 Sulphur: is determined from the washings obtained from a known
mass of coal, used in a bomb calorimeter for determination of a
calorific value. During this determination, S is converted into
sulphate. The washings are treated with barium chloride solution
and barium sulphate is precipitated. This precipitate is filtered,
washed and heated to a constant weight.
Percentage of S =
weight of BaSO4 obtained * 32 * 100
weight of coal sample taken * 233
2.4 Oxygen: it is obtained by difference
Percentage of O = 100 - % of ( C + H + S + N + ash)

Importance of ultimate analysis
1. Carbon and Hydrogen: greater is the percentage of of C and H, better is the
coal in quality and calorific value. Higher % of C reduces the size of the
combustion chamber required.
2. Nitrogen: has no calorific value and hence its presence is undesirable.
3. Sulphur: contributes to calorific value nevertheless it is undesirable as its
combustion products (acids from SO2 and SO3) have harmful effects of
corroding the equipment's and also cause atmospheric pollution.
4. Oxygen: it decreases the calorific value and also results in low coking power.
36

Numerical 1
Calculate the weight and volume of air required for the combustion
Of 3kg of Carbon.
Weight of C= 3kg, or 3000g
Moles of C = 3000/12 = 250
Moles of O2 required = 250
1 mole of gas at NTP = 22.4 litre
Therefore 250 mole of gas = 250*22.4 litre of O2
Since O2 is only 21% by volume, so volume of air = 250*22.4*100/21
= 2.67E4 litre
Weight of air required = 3*32/12*100/23 = 34.783kg
C + O2 CO2
37

Numerical2 Calculate the mass of the air needed for the complete combustion
of 5kg of coal in which C=80%, H=15% and O=5%
C=4kg, H=0.75kg, O=0.25kg
H2 + 1/2O2 H2O
Weight of oxygen required = [4*32/12] + [0.75*16/2] - 0.25
= 16.42kg
mass of air required = 16.416*100/23
= 71.37kg
C + O2 CO2
12 32
2 16
Mass percentage of oxygen in air is 23

Numerical 3: A coal sample was found to contain: C=66.2%, H=4.2%, O=6.1%,
N= 1.4%, S=2.9%, moisture=9.7% and ash =9.5% by weight. Calculate the
quantity of dry products of combustion, if 1kg of coal coal is burnt with 25%
excess air.
1kg of coal contains: C=662g, H=42g, O=61g, N=14g, S=29g, moisture=97g and ash=95g
Minimum wt of O required for complete combustion of 1Kg coal
= 662g X 32/12 + 42 X 16/2 + 29 X 32/32 - 61= 2069.3g
Minimum weight of air required=2069.3 X 100/23
= 8997g
Wt of CO2=662g X 44/12 = 2427.3g
Wt of SO2=29g X 64/32 = 58.0g
Wt of N2= Minimum amount of airX(125/100)X(77/100) + in coal
=8997g X 125/100X77/100 + 14 = 8763.6g
Weight of excess O=minimum wt of O2 X (25/100)
=2069.3 X 25/100 =517.3g
Total wt of dry products=2427.3+58.0+8763+517.3 = 11765.9g

Note: Do practice of numerical from the
reference books given in your syllabus
40

Petroleum
Petroleum or crude oil is a dark greenish-brown, viscous oil found in deep
earth’s crust. It is mainly composed of various hydrocarbons (like paraffin,
cycloparaffins, naphthalenes, olefins and aromatics), together with small
amount of organic compounds containing oxygen, nitrogen and sulphur.
The oil is usually found floating upon a layer of brine and has layer of gas
on top of it. The average composition of crude oil is C=79.5 – 87.1%,
H=11.5 - 14.8%, S=0.1-3.5%, N and O= 0.1 – 0.5%.

Petroleum
Crude oil
42

Crude oil: A mixture of hydrocarbons
43

Separation of crude oil into useful fractions
C1-C4
C5-C9
C10-C16
C10-C18
C17-C30
44
C5-C7

Fractional distillation of crude oil
45

Abundance of different fractions in crude oil
46

Classification of petroleum
1. Paraffin-base type crude is mainly composed of saturated hydrocarbons
from CH4 to C35H72 and a little of the naphthalenes and aromatics The
hydrocarbons from C18H38 to C35H72 are semi-solids, called waxes.
2. Asphaltic-base type crude contains mainly cycloparaffins or naphthalenes
with smaller amount of paraffin and aromatic hydrocarbons
octane
naphthalene
47

Classification of petroleum
3. Mixed-base type crude contains both paraffinic and asphaltic hydrocarbons
and are generally rich in waxes

1. Gasoline or petrol is obtained between 40-120 ⁰C and is mixture
of hydrocarbons such as C5H12 (pentane) to C8H18 (octane). Its
approximate composition is: C=84%, H=15%, N+S+O=1%. Its
calorific value is about 11,250kcal/kg. It is volatile, inflammable
and used as a fuel for internal combustion engines.
Important fractions of petroleum

2. Diesel oil is fraction obtained between 250-320 ⁰C and is a mixture of
C15H32 to C18H38 hydrocarbons. Its density is 0.86 to 0.95. Its calorific
value is about 11,000kcal/kg and is used as diesel engine fuel.

3. Lubrication oil: the length of the hydrocarbon chain varies between
12 to 50 carbon atoms. The shorter chain oil have lower viscosity
than the longer chain hydrocarbons. These are most widely used as
lubricants because they are cheap and quite stable under service
condition . However they possess poor oiliness as compared to
that of animal and vegetable oils. The oiliness of petroleum oils can
be increased by the addition of high molecular weights compounds
like oleic acid, stearic acid etc.
51

Abundance of different fractions in crude oil
Less in demand
More in demand
Conversion by cracking
52

Cracking:
Synthetic petrol
The decomposition of bigger hydrocarbons molecules into simpler, low
boiling hydrocarbons of lower molecular weight.
C10H22 C5H12 + C5H10
cracking
pentane pentene
B.p=174 ⁰C
B.p=36 ⁰C
53

Cracking:
1. Thermal cracking: the heavy oil are subjected to high temperature
(~500 ⁰C) and pressure (~100kg/cm2), when the bigger hydrocarbons
molecules break down to give smaller molecules of the paraffin, olefins
plus some hydrogen.
Synthetic petrol
54
Thermal Cracking Catalytic Cracking

Cracking:
1. Thermal cracking may be carried either in liquid-phase or vapor-phase
1.a) Liquid phase thermal cracking: the heavy oil is cracked at a suitable
temperature of 475-530 ⁰C and under a pressure of 100 kg/cm2. The
cracked products are then separated in a fractionating column. The
yield is 50-60 %.
1.b) Vapor-phase thermal cracking: the cracking oil is first vaporized and
then cracked at about 600-650 ⁰C and under a low pressure of
10-20kg/cm2. this process is suitable for those oils which may be
readily vaporized. It requires less time than liquid-phase method.
Synthetic petrol
55

Cracking:
2. Catalytic cracking: A suitable catalyst like aluminum silicate, Al2(SiO3)2
or alumina (Al2O3) is used to break the high molecular weight hydrocarbons.
The use of catalyst reduces the required temperature (420-450 ⁰C) and
pressure (1-5kg/cm2) of the cracking. The yield of the petrol is higher and
quality of the petrol produced is better.
Synthetic petrol
56
Advantages of Catalytic cracking:
• The yield of petrol is higher
• Quality of petrol is better
• A much lower pressure is needed
• The product contains less amount of sulphur
• The product contains higher fraction of aromatic thus
better antiknock characteristics

Synthetic petrol
2.a) Fixed bed catalytic cracking
Cracking:
Zircomium oxide catalyst

Synthetic petrol
Fixed bed catalytic cracking: the oil vapors are heated to cracking
temperatures (420-450 ⁰C) and then forced through a catalytic
chamber (containing artificial clay mixed with Zirconium oxide)
maintained at (425-450 ⁰C)and 1.5Kg/cm2 pressure. During their
passage through the tower, about 40%of the charge is converted
to gasoline and about 2-4% carbon is formed. The later gets
adsorbed on the catalyst bed. The vapors produced are then passed
through a fractionating column, where heavy oil fractions condense.
The vapors are then led a cooler, where some of the gases are
Condensed along-with gasoline and uncondensed gases move on.
The gasoline containing some dissolved gases is then sent to a
stabilized where the dissolved gases are removed and pure gasoline
is obtained.
58

1. Polymerization: the gases obtained as a by-product from cracking of heavy
oils, etc., contains olefins (like ethylene, propene and butenes) and alkanes
(such as methane, ethane, propane and butane). When this gaseous mixture
is subjected to high pressure and high temperature, with or without the
presence of catalyst, it polymerises to form higher hydrocarbons, resembling
gasoline, called polymer gasoline
CH3CH=CH2 + CH3CH2CH=CH2 CH2=CHCH2CH2CH(CH3)2
Pressure, heat
And/or catalyst
(propene) (butane-1) 5-methyl hexane-1
Synthetic petrol
59

1. Thermal polymerization in which polymerization of cracked gases is carried
out at 500-600 ⁰C and 70-350 kg/cm2 pressure. The product is gasoline and
gas oil mixture, which are separated by fractionation.
2. Catalytic polymerization is carried out in presence of catalyst like phosphoric acid.
In this case lower temperature of 150-200 ⁰C is employed. Products are gasoline
and unpolymerized gas. The later is separated and recycled for polymerization.
The polymerization is of two types:
Synthetic petrol
60

2. Fischer-Tropsh method:
The Fischer–Tropsch process involves a series of chemical reactions that produce
a variety of hydrocarbons, ideally having the formula (CnH(2n+2)). The more useful
reactions produce alkanes as follows:
(2n + 1) H2 + n CO → CnH(2n+2) + n H2O
where n is typically 10-20. The formation of methane (n = 1) is unwanted. Most of
the alkanes produced tend to be straight-chain, suitable as diesel fuel. In addition
to alkane formation, competing reactions give small amounts of alkenes, as well as
alcohols and other oxygenated hydrocarbons.
2n H2 + n CO → CnH2n + n H2O
Synthetic petrol
61

Synthetic petrol
Fe2O3 + H2S → Fe2S3 + 3H2O removal of H2S
Fe2S3 + 4O2 → 2FeO + 3SO2↑
4FeO + O2 → 2Fe2O3 regeneration of catalyst
Fe2O3 Na2CO3 removes organic sulphur compounds
62
Pressure 5-25atm
Temperature 200-300 ⁰C

Working: water gas (CO+H2) is mixed with H2 and purified by passing through
Fe2O3 (to remove H2S) and then into mixture of Fe2O3.Na2CO3 (to remove organo
sulphur compounds). The purified gas is then compressed (~5-25 atm) and then
led through a convertor ( containing catalyst) maintained at about 200-300 ⁰C. A
mixture of saturated and unsaturated hydrocarbons are formed.
(2n + 1) H2 + n CO → CnH(2n+2) + n H2O
2n H2 + n CO → CnH2n + n H2O
The reaction is exothermic, so out coming gaseous mixture is led to a cooler,
where the liquid resembling to crude oil is obtained which is then fractionated
to give gasoline and high boiling heavy oil
Synthetic petrol
63

3. Bergius process
Synthetic petrol
64
Pressure 200-250 atm
Temperature 450 ⁰C
Yield of gasoline is ~60% of the coal dust used

3. Bergius process
The low ash coal is finely powdered and made into a paste with heavy oil and then
a catalyst (composed of tin or nickel oleate) is incorporated. The whole is heated
with H2 at 450 ⁰C and under a pressure of 200-250atm for about 1.5 hours, during
which H2 combines with coal to form saturated hydrocarbons, which decompose at
prevailing temperature and pressure to yield low boiling liquid hydrocarbons. The
issuing gases are led to condenser , where a liquid resembling crude is obtained,
which is then fractionated to give (1) gasoline, (2) middle oil, (3) heavy oil.
The heavy oil is again used for making paste with fresh coal dust. The middle oil is
hydrogenated in vapor phase in the presence of catalyst to yield more gasoline.
The yield of gasoline is about 60% of the coal dust used.
Synthetic petrol

Numerical: A petrol sample contains 84% Carbon and 16% hydrogen by weight. Its
flue gas compositional data by volume is as under:
CO2=12.1%, CO=1.1%, Oxygen=1.3%, Nitrogen=85.5%.
Calculate weight of minimum air needed for complete combustion of 1Kg of petrol.
1kg of petrol; C=840g, H=160g
C + O2 CO2
12 32
H2 + 1/2O2 H2O
2 16
Wt of oxygen needed=160*16/2=1280g
Total=3520g
weight of minimum air needed for complete combustion of 1Kg of petrol=3520*100/23
=15304g
Wt of oxygen needed= 840*32/12=2240g
66

67
A car without lubricant will explode in less than 15 minutes
Lubricants and lubrication

Lubricants and lubrication
Lubricants: Any substance introduced between two moving/sliding surfaces
with a view to reduce the frictional resistance between them, is known as
lubricant. The main purpose of lubricant is to keep the sliding/moving
surfaces apart.
Lubrication: the process of reducing frictional resistance between moving
/sliding surfaces by the introduction of lubricants in-between them.
68

Function of lubricants:
1. It reduces surface deformation, wear and tear, because the
direct contact between the rubbing surfaces is avoided
2. It reduces the loss of energy in the form of heat
3. It reduces expansion of metal by local frictional heat.
4. It avoids seizure of moving surfaces
5. It reduces running and maintenance cost of the machine
6. It also sometimes acts as a seal
7. It avoids unsmooth relative motion
69

70
Mechanism of lubrication
1. Fluid-film or thick-film or hydrodynamic lubrication:

1. Fluid-film or thick-film or hydrodynamic lubrication:
The lubricant Film covers/fills the irregularities of the
sliding/moving surfaces and Forms a thick layer (~1000Å) in-between them,
so that there no direct contact between the material surfaces. This consequently
reduces the wear. The resistance to movement is only due the internal resistance
between the particles of the lubricant moving over each other. The lubricant
chosen should have the minimum viscosity under working conditions and at
the same time it should remain in place and separate the surfaces.
Hydrocarbon oils (12-50 carbon atoms) are considered to be satisfactory
lubricants for thick-film lubrication. In order to maintain the viscosity of the oil in all
seasons of year, ordinary hydrocarbon lubricants are blended with selected long
chain polymers
72

73
2. Boundary or thin-film lubrication:

2. Thin film lubrication: this type of lubrication is preferred where a continuous
film of lubricant can not persist . In such cases, the clearance space between the
moving/sliding surfaces is lubricated by such a material which can get
adsorbed on both the metallic surfaces by either physical or chemical forces.
This adsorbed film helps to keep the metal surfaces away from each other at
least up to a height of the peaks present on the surface.
Vegetable and animal oils and their soaps can be used in this type of lubrication.
Although these oils have good oiliness, they suffer from the disadvantage that
they will break down at high temperatures. On the other hand, mineral oils are
thermally stable and the addition of vegetable/animal oils to mineral oils, their
oiliness can also be brought up. Graphite and molybdenum disulphide are also
suitable for thin film lubrication
74

3. Extreme pressure lubrication: when the moving/sliding surfaces are under
very high pressure and speed, a high local temperature is attained under such
conditions, liquid lubricants fails to stick and may decompose and even vaporize.
To meet these extreme conditions, special additives are added to mineral oils.
These are called extreme pressure additives. These additives form more durable
films on metal surfaces.
Important additives are organic compounds having active radicals or groups
such as chlorine (as in chlorinated esters), sulphur (as in sulphurized oils) or
phosphorous (as in tricrecylphosphate). These compounds reacts with metallic
surfaces, at existing high temperatures, to form metallic chlorides, sulphides and
phosphides.
75

Classification of lubricants
Lubricants can be broadly classified, on the basis of their physical
state as follows:
1. Liquid lubricants and lubricating oils
2. Semi-solid lubricants or greases,
3. Solid lubricants
76

1. Liquid lubricants and lubricating oils: liquid lubricants are further classified
into three categories;
a) animal and vegetable oils,
b) Mineral or petroleum oils
c) Blended oils
77

1.a) animal and vegetable oils: animal oils are extracted from the crude fat and
vegetable oils such as cotton seed oil and caster oils. These oils possess good
oiliness and hence they can stick on metal surfaces effectively even under
elevated temperatures and heavy loads. But they suffer from the
disadvantages that they are costly, undergo easy oxidation to give gummy
products and hydrolyze easily on contact with moist air or water. Hence they
are only rarely used these days for lubrication. But they are still used as
blending agents in petroleum based lubricants to get improved oiliness.
78

1.b) Mineral or petroleum oils: these are basically lower molecular weight
hydrocarbons with about 12 to 50 carbon atoms. As they are cheap,
available in abundance and stable under service conditions, hence they
are widely used. But the oiliness of mineral oils is less, so the addition
of higher molecular weight compounds like oleic acid and stearic acid
increases the oiliness of mineral oil.
79

1.c) Blended oils: no single oil possesses all the properties required for a good
lubricant and hence the addition of proper additives is essential to make
perform well. Such additives added lubricating oils are called blended oils.
Example: the addition of higher molecular weight compounds like oleic acid,
stearic acid, palmitic acid, etc. or vegetables oil like coconut oil, castor oil, etc
increases the oiliness of mineral oil.
80

Formulation of lubricants
• Typically lubricants contain 90% base oil and less than 10%
additives
• Base :
– most often petroleum fractions (called mineral oils)
– vegetable oils or synthetic liquids such as hydrogenated
polyolefins, esters, silicones, fluorocarbons are sometimes
used as base oils
81

Formulation of lubricants
• The primary function of the base fluid:
– to lubricate and act as a carrier of additives
• The function of additives:
– to enhance an already existing property of the base fluid
viscosity, viscosity index, pour point, oxidation resistance
– to add a new property
• cleaning/suspending ability, antiwear performance,
corrosion control
82

Types of additives
• Some additives impart new and useful properties to the
lubricant
• Some enhance properties already present
• Some act to reduce the rate at which undesirable changes
take place in the product during its service life
83

Typical additives
• Friction modifiers
• Anti-wear agents
• Extreme-pressure additives
• Anti-oxidation additives
• Rust and corrosion inhibitors
• Foam inhibitors
• Oiliness agents
• Detergents and dispersants
• Alkaline agents
• Pour point depressants (PPD)
• Viscosity index improvers
84

1) Oiliness carriers: the addition of higher molecular weight compounds like
oleic acid, stearic acid, palmitic acid, etc. or vegetables oil like coconut oil,
castor oil, etc increases the oiliness of mineral oil.
2) Extreme Pressure Additives: Under extreme pressure, a thick film of oil is
difficult to maintain. High pressure additives contain materials which are
either adsorbed on the metal surface or react chemically with the metal,
producing a surface layer of low shear strength on the metal surface.
Examples: fatty ester, acids, organic materials which contain sulphur,, organic
chlorine compounds, organic phosophorous compounds etc.
Additives in Blended oils
85

3) Thickeners: such as polystyrene, polyesters etc., are materials of high molecular
weight between 300 to 3000. They are added in lubricating oil to increase the
viscosity
86
polystyrene

4) Antioxidants or inhibitors: when added to the oil retard oxidation of the oil
by getting themselves preferentially oxidized. They are particularly added
added in lubricants used for internal combustion engines. The antioxidants are
aromatic phenols, or amino compounds.
87

5) Foam Inhibitors: Foaming of lubricants is a very undesirable effect
- can cause enhanced oxidation by the intensive mixture with air
88
Dimethylsilicones (dimethylsiloxanes)

2.) semi-solid lubricants or grease: a semi-solid lubricant obtained by combining
oil with thickening agents. Lubricating oil is the principal component and it
can be either petroleum oil or a synthetic hydrocarbon of low to high viscosity.
The thickeners consists primarily of special soaps of Li, Na, Ca, Ba, Al, etc.
Non-soap thickeners include carbon black, silica gel, polyureas and other
syntheic polymers, clays etc. Grease can support much heavier load at lower
speed. Internal resistance of grease is much higher than that of lubricating oil;
therefore it is better to use oil instead of grease. Compared to lubricating oils
grease can not effectively dissipate heat from the bearings, so work at
relatively lower temperature.
2. semi-solid lubricants or grease
89

2.) Classification of grease:
Greases are classified after the soap used in their manufacture. Important
greases are
2.1 Calcium based greases or cup greases: are emulsions of petroleum oils with
calcium soaps. They are prepared by adding calcium hydroxide to a hot oil.
They are insoluble in water and are the cheapest
2.2 Soda base grease: are petroleum oils, thickened by mixing sodium soaps.
They are not water resistant, because the sodium soap content is water soluble.
However they can be used upto 175⁰C. They are suitable in ball bearings.
90

2.) Classification of grease:
2.3 Lithium based greases : are petroleum oils thickened by mixing lithium soaps.
They are water resistant and suitable for use at low temperatures (<15⁰C).
2.4 Axle grease: are very cheap resin greases, prepared by adding lime to resin and
fatty oils. The mixture is thoroughly mixed and allowed to stand, when grease
floats as stiff mass. Fillers like talc and mica also added to them. They are water
resistant.
91

3.) solid lubricants :they are preferred where (1) the operating conditions are
such that a lubricating film cannot be secured by the use of lubricating oils
or grease, (2) contamination of lubricating oil or grease is unacceptable, (3) the
operating temperature or load is too high, even for grease to remain in position,
(4) combustible lubricants must be avoided, they are used either in the dry
powder from or with binders to make them stick firmly to the metal surface
while in use. They are available as dispersions in non-volatile carriers like soaps,
fats, waxes, etc and as soft metal films.
The most common solid lubricants are graphite, molybdenum disulphide, tungten
disulphide and zinc oxide. They can withstand temperatures up to 650 ⁰C and can
be applied in continuously operating situations. They are also used as additives to
mineral oils and greases in order to increase the load carrying capacity of the
lubricant. Other solid lubricants in use are soapstone and mica.
92

3.1 Graphite: It is the most widely used of all the solid lubricants and can be used
either in the powdered form or in suspension. It is soapy to touch; non-flammable
and stable upto a temperature of 375 ⁰C. Graphite has a plate like structure and the
layers of graphite sheets are arranged one above the other and held together by
van der Waal’s forces. These parallel layers which can easily slide one over other
make graphite an effective lubricant. Also the layer of graphite has a tendency to
absorb oil and to be wetted of it.
Solid lubricants: examples
93

3.2 Molybdenum disulphite: It has a sandwich like structure with a layer of
molybdenum atoms in between two layers of sulphur atoms. Poor interlaminar
attraction helps these layers to slide over one another easily. It is stable up to a
temperature of 400 ⁰C.
Solid lubricants: examples
94

Selection of lubricants: In selecting a lubricant for a particular job, the service
condition requirements are to be related to the properties of the lubricant.
The properties of a properly selected lubricant should not change under
service conditions. The properties of a properly selected lubricant should
not change under service conditions. Selection of a lubricant for a few typical
jobs are illustrated as follows:
1. Lubricants for cutting tools: Cutting fluids are lubricants used in cutting, turning,
and grinding of metals. The main functions of cutting fluids are: a) to cool the tool
b) to cool the metal work-piece so as to prevent dimensional inaccuracies, c) to
reduce power consumption by lubrication action, d) to improve surface finish
Two situations can be there in cutting tool:
Selection of lubricants
95

(1.a) For heavy cutting: the most effective lubricants are cutting oils. The
cutting oils are essentially mineral oils of low viscosities containing
additives like fatty oils, sulphurized fatty oils which by virtue of their
polar groups attach themselves to the surface of continuously
exposed fresh metals.
(1.b) In light cutting: the most effective lubricants are oil-emulsions. Oil-
emulsions have somewhat smaller lubricating effect than cutting
oils, but they are more efficient as cooling media, due to high heat
capacity of water, which is present in them as an external phase.
96

2. Lubricants for internal combustion engines:
In internal combustion engines, the lubricant is to be exposed to
high temperatures. Therefore the lubricant should possess high viscosity
index (i.e. low variation of viscosity with temperature) and high thermal
stability. Petroleum oils containing additives, which impart high viscosity
index and oxidation stability to them, are used as lubricants for internal
combustion engines.
97

3. Lubricants for gears:
are subjected to extreme pressures. So they should possess good
oiliness, ii) not to be removed by centrifugal force, iii) possess high resistance
to oxidation, iv) have high load carrying capacity. Thick mineral oils
containing extreme pressure additives are employed.
98

4. Lubricants for transformers:
The functions of the lubricating oil in the transformer are to
insulate the windings and to carry away the heat generated. The oil must
possess good dielectric properties, chemically inert and low viscosity. Highly
refined mineral oils of high insulating quality, optimum oxidation resistance
and chemical stability are employed.
99

fuels and lubricants.pdf

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to fuels and lubricants.pdf

Similar to fuels and lubricants.pdf (20)

Recently uploaded

Recently uploaded (20)

fuels and lubricants.pdf