Energy saving and energy science

1. B.E. SEMESTER-I/II
ENGINEERING CHEMISTRY
ENERGY SCIENCE

2. CONTENTS OF ENERGY SCIENCE- FUEL
 Introduction of chemical fuel its classification,
 calorific value,Gross and Net calorific value and its relation,
 Analysis of coal : Proximate analysis,Ultimate Analysis and their
significance,
 Characteristic of good fuel,
 cracking of petroleum fractions,use of gasoline and diesel in IC
engine,
 Knocking
 octane number,
 cetane number,
 Numerical based on combustion.
 Mass to mass
 Volume to volume
 Less air supplied type

3. FUEL
 Definition of Fuel
 Types of fuel
 Units of heat energy
 Calorific value of fuel
Gross calorific value
 Net calorific value
 Characteristics of good fuel

4. FUEL
 DEFINATION:
 Fuel is a combustible substance which on
burning in presence of air(oxygen) gives
large amount of heat that can be use
economically for domestic and industrial
purposes.

5. CLASSIFICATION OR TYPES OF FUEL
Solid
Liquid
Gas
FUEL
Natural (Primary) Artificial (Secondary)
Wood , Peat , Coal Coke , Charcoal , briquette
Petroleum or crude oil Petrol , Kerosene , Diesel ,
Coal tar
Natural gas
Producer gas (CO+N2)
Water gas (CO+H2)
Biogas , oil gas

6. UNITS OF HEAT ENERGY
1. Calorie :- Amount of heat required to raise the
temperature of 1 gm of water by 1 degree Centigrade
(15-16 C)
1 cal = 4.185 J
2. British Thermal Unit :- Amount Of Heat Required to
raise the temperature of 1 pound of water by 1 degree
Fahrenheit.
1B.T.U = 252 cal. 1 Kcal = 3.968 B.T.U
3.Centigrade heat unit :- Amount Of Heat Required to
raise the temperature of 1 pound of water by 1 degree
Centigrade (15-16 C)
1 Kcal = 3.968 B.T.U = 2.2.C.H.U.

7. Calorific value of fuel
 “ The Total amount of heat liberated when unit mass or unit
volume of fuel burnt completely in excess of air ”
 C + O2  CO2 + 97644 cal.
 Fuel air
 12 gm carbon = 97644 cal , 1 gm carbon = 8137 cal
 H2 + ½ O2  H2O + 69000 cal.
 Fuel air
 2 gm Hydrogen = 69000 cal , 1 gm Hydrogen = 34500
cal.
 Mean Calorific Value = (% of carbon X 8137 ) + (% of
Hydrogen X 34500) / 100

8. Calorific Value
 It is the most important characteristic property of
any fuel. Calorific value may be defined as “the
amount of heat energy liberated when unit mass or
unit volume of a fuel is burnt completely in excess
of air ”.
There are two types of calorific value of fuel
 1.Gross or Higher Calorific Value (GCV)
 2.Net or Lower Calorific value (NCV)

9. Calorific Value
 Gross or Higher Calorific Value (GCV)
 The total heat generated when a unit mass/volume
of a fuel is completely burnt and the products of
combustion are cooled to room temperature.
 For example, when a fuel containing hydrogen is
burnt, it under goes combustion and will be
converted to steam. If the combustion product is
cooled to room temperature, the steam gets
condensed into water and the latent heat is evolved.
Therefore the latent heat of combustion of
condensation of ‘steam’ so liberated is included in
gross calorific value.

10. Calorific Value
 Net or Lower Calorific value (NCV)
The net heat produced when a unit mass or unit
volume of fuel is completely burnt and the products
of combustion are allowed to escape.
 NCV = GCV – Latent heat of condensation
of steam produced
 H2 + ½ O2 H2O
 2gms 16gms 18gm
 1 8 9
1 part by weight of H2 produces 9 parts by weight of H2O
 The latent heat of steam is 587 cal/gm.
 NCV = GCV – H/100 × 9 ×587 cal/g
 NCV = GCV – 0.09 H ×587 cal/g
 where , H = % of H2 in the fuel.

11. COAL-SOLID FUEL
 Analysis of Coal:-
 The analysis of coal is helpful in its ranking. The
assessment of the quality of coal is carried out
by these two types of analysis.
 A) Proximate analysis
 B) Ultimate analysis
 A. Proximate Analysis:
 In this analysis, the percentage of carbon is
indirectly determined. It is a quantitative
analysis of the following parameters.
1. Moisture content
2. Volatile matter
3. Ash
4. Fixed carbon

12. 1.Determination of moisture content in coal
Procedure : About 1 gm of powdered, air dried coal
sample is heated in silica crucible at 105 to 110 °C for
one hour. Percentage of moisture can be calculated
from the loss in weight of the coal sample as
Observations:
1. Weight of empty silica crucible= W1 gm
2. Weight of silica crucible plus coal sample= W2 gm
3. Weight of silica crucible plus coal sample
after heating at 105 to 110 °C for one hour= W3gm
Silica Crucible with Lid
Electric Oven
Glass Desiccator with Lid

13. 1.Determination of moisture content in coal
% of moisture in coal = W2 - W3 / W2 – W1 × 100
Significance of Moisture
Moisture content in coal is undesirable because it,
i) Reduces Calorific Value of coal.
ii)Increases the consumption of coal for heating
purpose.
iii) Lengthens the time of heating.
Hence, lesser the moisture content, better is the
quality of coal.

14. 2. Determination of Volatile Matter (V.M.) in coal
Procedure : After the analysis of moisture content the crucible
with residual coal sample is covered with a lid, and it is heated at 925
± 20 °C for 7.0 minutes in a muffle furnace. Percentage of volatile
matter can be calculated from the loss in weight of the coal sample as
Observations:
1. Weight of empty silica crucible= W1 gm
2. Weight of silica crucible plus moisture free coal sample= W3gm
3. Weight of silica crucible plus coal sample
after heating at 925 ± 20 °C for 7.0 minutes = W4 gm
Silica Crucible with Lid Glass Desiccator with Lid
Muffle Furnace

15. 2. Determination of Volatile Matter (V.M.) in coal
% of Volatile Matter (V.M.) in coal = W3 – W4 / W3 – W1 × 100
Significance of Volatile Matter:
During burning of coal, certain gases like CO, CO2, CH4, H2, N2, O2,
hydrocarbons etc. that come out are called volatile matter of the
coal.
The coal with higher volatile content,
 Ignites easily (i.e. : it has lower ignition temperature)
 Burns with long yellow smoky flame
 Has lower Calorific Value
 Will give more quantity of coal gas when it is heated in absence
of air.

16. 3.Determination of Ash content in coal
Procedure : After the analysis of volatile matter the
crucible with residual coal sample is heated without lid
at 700 ± 50 °C for 30 TO 40 minutes in a muffle
furnace OR till ash is formed in the crucible.
Observations:
1. Weight of empty silica crucible= W’1 gm
2. Weight of silica crucible plus coal sample= W’2 gm
3.Weight of silica crucible plus ash formed = W’3
Silica Crucible with Lid Glass Desiccator with Lid
Muffle Furnace

17. 3.Determination of Ash content in coal
Percentage of ash content can be calculated from the
weight of the ash formed in the crucible as
% of Ash in coal = W’3 – W’1 / W’2 – W’1 × 100
Significance of Ash:
High ash content in coal is undesirable because it
(a) increases transporting, handling, storage costs,
(b) is harder and stronger,
(c) has lower Calorific Value.

18. 4.Determination of fixed carbon content in
coal
It is determined by subtracting the sum of total
moisture, volatile matter and ash contents from 100.
Significance of Fixed Carbon :
It is the pure carbon present in coal. Higher the fixed
carbon content of the coal, higher will be its Calorific
Value.
% of fixed carbon = 100 - % of [moisture + V.M + ash]

19. ANALYSIS OF COAL
2. ULTIMATE ANALYSIS OF COAL
 It means finding out the weight
percentage of carbon, hydrogen,
nitrogen, sulphur, ash and oxygen from
the coal .
 This analysis gives the elementary
constituents of coal.
 It is useful to the designer of coal burning
equipments and auxiliaries.

20. Ultimate Analysis:
 1. Determination of Carbon and hydrogen in coal:
 A known amount of coal is burnt in presence of
oxygen there by converting carbon and hydrogen of
coal into
 CO2 (C + O2 → CO2) and
 H2O (H2 + ½ O2 → H2O) respectively.
 The products of combustion (CO2 and H2O) are made
to pass over weighed tubes of anhydrous CaCl2 and
KOH, which absorb H2O and CO2 respectively.
 The increase in the weight of CaCl2 tube represents
the weight of water formed while increase in the
weight of KOH tube represents the weight of CO2
formed. % of carbon and hydrogen in coal can be
calculated as follows.

21. ESTIMATION OF C AND H
C + O2 CO2
12gm(coal) 32 44 gm
2KOH + CO2 K2CO3 + H2O
TUBE
H2 + 1/2O2 H2O
2gm 16 18 gm
CaCl2 + 7H2O CaCl2.7H2O

22. Determination of Carbon and hydrogen in coal:
Let X - the weight of coal sample taken
Y - the increase in the weight of KOH tube
Z - the increase in the weight of CaCl2 tube
% of C in coal =
Increase in weight of KOH tube × 12 ×100
weight of coal X 44

23. Determination of Carbon and hydrogen in coal:
Let X - the weight of coal sample taken
Y - the increase in the weight of KOH tube
Z - the increase in the weight of CaCl2 tube
% of Hydrogen in coal =
Increase in weight of CaCl2 × 2 × 100
weight of coal X 18

24. ESTIMATION OF N BY KJELDAHL’S METHOD
 Determination of Nitrogen in coal:
 In Kjeldahl’s flask add accurately weighed powdered
coal and heated with concentrated H2SO4 and CuSO4
as a catalyst.
 The solution becomes clear when all the nitrogen is
converted into ammonium sulphate(NH4)2SO4. Then
it is treated with excess of NaOH which convert
ammonium sulphate into ammonia NH3. The
liberated ammonia is distilled over and absorbed in
a known volume of standard (N/10) H2SO4 solution.
 From the volume of H2SO4 neutralized by liberated
ammonia, the percentage of Nitrogen in coal,
calculated as follows:

25. (NH4)2SO4
(NH4)2 SO4 + 2NaOH Na2SO4 + 2NH3 + 2H2O
H2SO4
2NH3 + H2SO4 (NH4)2 SO4

26. ESTIMATION OF N2 BY KJELDAHL’S METHOD
 H2SO4 +2NH3 (NH4)2SO4
 1000ml,1N,H2SO4=17gmsof NH3=14 gms of Nitrogen
 1 ml,1N,H2S04 =14X10-3 gms of Nitrogen
 Let (V ml) X (x N H2SO4) = (V ml) X (x Normal)X
14X10-3 gms of Nitrogen
 (V ml) X (x Normal)X 14X10-3 gms of Nitrogen is
present in Y gm of coal
 Y gm coal= (V ml) X (x Normal)X 14X10-3 gms of
Nitrogen
 100 gm coal= (V ml) X (x Normal)X 14X10-3 gms of
NitrogenX100/ Y
% OF N2= Normality x consumed Acid of Volume x 1 .4
Weight of coal sample(Y)

27. ESTIMATION OF SULPHUR
S
O2
H2SO4
BaCl2
BaSO4 (Ba = 137 , S = 32 , O = 16)
32 233
H2SO4 + BaCl2 BaSO4 + 2HCl
Washing Precipitate
Sulphur is determined from the washings obtained
from the known mass of coal, used in bomb
calorimeter for determination of a calorific value.
 During this determination, S is converted in to
Sulphate.
The washings are treated with Barium chloride
solution, when Barium sulphate is precipitated.
 This precipitate is filtered, washed and heated to
constant weight.

28. ESTIMATION OF SULPHUR
X gm of coal contains 32/233 X M gms of sulphur
100 gms of coal contains 32/233 X M X 100/X
% OF S = Weight of BaSO4 Formed X32 X100
Weight of coal taken X 233

29. Ultimate analysis: determination of ash
 Ash: The residual coal taken in the crucible and then
heated without lid in a muffle furnace at 750±50 c for
½ hour. The crucible is then taken out, cooled first in
air, then in desiccators and weighed. Heating, cooling
and weighing are repeated, till a constant weight is
obtained. The residue is reported as ash on
percentage-basis. Thus,
 Weight of ash left
Percentage of ash = ------------------------ X 100
 Weight of coal take

30. Ultimate analysis: determination of oxygen
 Oxygen:
 It is determined indirectly by deducting the combined
percentage of carbon, hydrogen, nitrogen, sulphur and ash
from 100.
 Percentage of O2 = 100 – % (C + H + S + N + Ash)

31. Significance of Ultimate Analysis
 Carbon and Hydrogen: Greater the percentage of carbon and
hydrogen better is the coal in quality and calorific value.
However, hydrogen is mostly associated with the volatile mater
and hence, it affects the use to which the coal is put. Nitrogen:
Nitrogen has no calorific value and hence, its presence in coal is
undesirable. Thus, a good quality coal should have very little
Nitrogen content.
 Sulphur: Sulphur, although contributes to the heating value of
coal, yet on combustion produces acids like SO2, SO3, which
have harmful effects of corroding the equipments and also cause
atmospheric pollution. Sulphur is, usually, present to the extent
of 0.5 to 0.3% and derived from ores like iron, pyrites, gypsum,
etc., mines along with the coal. Presence of sulphur is highly
undesirable in coal to be used for making coke for iron industry.
Since it is transferred to the iron metal and badly affects the
quality and properties of steel. Moreover, oxides of sulphur
pollute the atmosphere and leads to corrosion

32. Significance of Ultimate Analysis
 Ash: Ash is a useless, non-combustible matter, which reduces the
calorific value of coal. Moreover, ash causes the hindrance to the
flow of air and heat, thereby lowering the temperature. Hence,
lower the ash content, better the quality of coal. The presence of
ash also increases transporting, handling and storage costs. It
also involves additional cost in ash disposal. The presence of ash
also causes early wear of furnace walls, burning of apparatus and
feeding mechanism.
 Oxygen: Oxygen content decreases the calorific value of coal.
High oxygen-content coals are characterized by high inherent
moisture, low calorific value, and low coking power. Moreover,
oxygen is a combined form with hydrogen in coal and thus,
hydrogen available for combustion is lesser than actual one. An
increase in 1% oxygen content decreases the calorific value by
about 1.7% and hence, oxygen is undesirable. Thus, a good
quality coal should have low percentage of oxygen.

33. CHARACTERISTICS OF GOOD FUEL
1.High calorific value :- amount of heat librated depends upon
calorific value.
2 Moderate ignition temperature:- ignition temperature is the
lowest temperature to which the fuel must be pre heated so that
it starts burning smoothly. low ignition temperature is dangerous
for storage and transport of fuel can causes fire hazards.
3.Low moisture content:- it reduces the heating value and
involves loss of money because it paid at a same rate as fuel.
4.low non combustible matter content:- non combustible matter
after burning of fuel remains are clinkers, ash, excess amount of
combustible matter reduces heating value
5.Moderate velocity of combustion:-
6.Products of combustion should not be harmful.(CO,SO2,H2S,)
7. low cost
8.Easy to Transport.
9.fuel should not under go spontaneous combustion.
10 fuel should burn in air with efficiency without much smoke.
11.Storage cost in bulk should be low

34. FUEL(PETROLEUM)
What is Petroleum?
What is Petroleum?
•
• Crude Oil
Crude Oil
•
• Natural Gas
Natural Gas

35. FUEL(PETROLEUM)
Oil and Gas Supply More Than 60%
Oil and Gas Supply More Than 60%
of World Energy Consumed
of World Energy Consumed
Oil (39%) Gas (23%)
Coal (24%) Nuclear (6%)
Hydroelectric (7%) Renewables (1%)
Source: EIA, Annual Energy Review, 2002

36. On average, crude oils are made of the following
elements or compounds:
 Carbon - 84%
 Hydrogen - 14%
 Sulfur - 1 to 3% (hydrogen sulfide, sulfides,
disulfides, elemental sulfur)
 Nitrogen - less than 1% (basic compounds with
amine groups)
 Oxygen - less than 1% (found in organic
compounds such as carbon dioxide, phenols,
ketones, carboxylic acids)
 Metals - less than 1% (nickel, iron, vanadium,
copper, arsenic)
 Salts - less than 1% (sodium chloride, magnesium
chloride, calcium chloride
COMPOSITION OF PETROLEUM

37. REFINING OF PETROLEUM
How do we refine it?
How do we refine it?
REFINERY
The process in which crude oil is separated in
to various useful fractions having different
boiling points by fractional distillation.

40. FRACTIONAL DISTILLATION
 Construction :- It is a specially designed tall fractionating tower. It consists
of a large number of horizontal stainless steel trays.
 Each tray having number of chimneys covered with loose caps.
 Each tray is connected to downward pipe which carries the liquid to the
next lower pipe.
 Working :- crude oil is heated to about 400 C in furnace and hot vapors are
passed near bottom of tower.
 The tower is hot at bottom and cooled at upper end as the vapors of the oil
rise up in the tower they are gradually cooled down and fractional
condensation takes place through chimneys in trays at different heights of
column.
 The highest boiling fraction condense first at the bottom and lowest boiling
fraction condense later at the top.
 The outlet are provided in the side of column at suitable heights to withdraw
a number of fractions.
 The uncondensed gases escape at the top of the fractionating tower these are
LPG ( Methane, Ethane ,Propane and Butane)

41. USEFUL FRACTIONS
Name
Number of
Carbon Atoms
Boiling Point
(°C)
Uses
Refinery Gas 3 or 4 below 30
Bottled Gas
(propane or butane).
Petrol 7 to 9 100 to 150
Fuel for car
engines.
Naphtha 6 to 11 70 to 200
Solvents
and used in petrol.
Kerosene 11 to 18 200 to 300
Fuel for aircraft
and stoves.
Diesel Oil 11 to 18 200 to 300
Fuel for road vehicles
and trains.
Lubricating Oil 18 to 25 300 to 400
Lubricant for engines
and machines.
Fuel Oil 20 to 27 350 to 450
Fuel for ships
and heating.
Greases and Wax 25 to 30 400 to 500
Lubricants
and candles.
Bitumen above 35 above 500
Road surface
and roofing.

42. Need Of Cracking Process
 Petroleum fossil fuels are burned in internal combustion
engines to provide power for ships, automobiles,
aircraft engines, lawn mowers, chainsaws, and other
machines.
 The different boiling points allow the hydrocarbons to
be separated by the process of distillation.
 .The Oil refinery provides the liquid fractions (hydro
carbon) with high molecular weight which do not burn
smoothly as a fuel in petrol engine
 The lighter liquid products are in great demand for use
in internal combustion engines, a modern refinery will
convert heavy hydrocarbons and lighter gaseous
elements into these higher value products.
 Lighter hydro carbon used as fuel burns smoothly in
Petrol Engine.

43. CRACKING OF PETROLEUM
Cracking is defined as the process of decomposition of
the higher molecular weight hydrocarbon having high
boiling point to the low molecular weight hydrocarbon
having low boiling point.
eg. C10H22
Cracking
C5H12 + C5H10
Decane
B.P.= 1740C
n-Pentane
B.P.=360C
n-Pentene
B.P.=360C
1. Higher hydrocarbons are converted to lower hydrocarbons.
2. Saturated hydrocarbons are converted to unsaturated
hydrocarbons.
3. Higher boiling point hydrocarbons are converted to lower
boiling point hydrocarbons

44. TYPES OF CRACKING
Liquid phase
thermal cracking
(500-600 0C,100Kg./cm2)
Thermal cracking Catalytic cracking
Vapour phase
thermal cracking
(600-700 0C,20Kg./cm2)
Vapour phase
catalytic cracking
Fixed bed
catalytic cracking
Moving bed (fluid)
catalytic cracking

45. Thermal cracking
 In this method heavy oil fractions are subjected to the action
of high pressure and temperature. Due to this bigger
molecule get broken in to smaller molecule This process is
carried out as follows.
 1.Liquid phase thermal cracking :- In this process heavy oil is
cracked or heated at a temperature of 475 to 530 c under
high pressure of 100 kg/cm2. to keep reaction products in
liquid state. The cracked products are separated in
fractionating column.
 2.Vapour phase thermal cracking :- In this process heavy oil
is first vaporized and then heated at a temperature of 600 c to
650 c under low pressure of 10 -20 kg/cm2. The cracked
products are separated in fractionating column this process
required less time and is suitable for liquid like kerosene
which readily get vaporized

46. Catalytic Cracking
 This process of cracking is carried out in presence of catalyst like Alumina
(Al2O3 ) or Aluminum Silicate ( Al2(SiO3)3) to improve quality and yield of
gasoline is called catalytic cracking.
 The catalytic cracking is carried out by two methods
 1.FIXED BED CATALYTIC CRACKING
 2. MOVING BED CATALYTIC CRACKING

47. FIXED BED CATALYTIC CRACKING

48. 1.FIXED BED CATALYTIC CRACKING
 1. The Oil vapors' are heated in preheated (400-500 C) , Pressure
1.5kg/cm2 and passed through a catalytic chamber ( artificial clay
mixed with bauxite ).
 2.The 30-40% heavy oil converted to gasoline with 4% carbon deposit
on catalyst bed
 3.Cracked vapors are then send to fractionating column for separation
 4.Gasoline vapors are condensed in cooler and passed through stabilizer
where dissolved gases from petrol get removed.
 5.When large carbon deposited on catalyst bed it stop functioning .Then
it is reactivated by burning off the carbon by steam of hot air

49. MOVING(FLUID) BED CATALYTIC CRACKING

50. 2. MOVING BED CATALYTIC CRACKING
 1.In this process use of fine powder of catalyst get circulated in gas
stream and behave like fluid therefore it is called MBCC
 2.Heavy oil mixed with fine powder and cracked inside reactor maintain
at 500 C.
 3.The process produces small hydrocarbon vapors and some carbon
which deposit on catalyst particles.
 4.These heavy particle sent to regeneration unit ( 600 C ) where
deposited carbon burn off to produce fresh catalyst particle.
 5.Cracked vapors are then passed through centrifugal separator called
cyclone which only allowed to pass cracked vapors and not the catayst.
 6.Cracked vapors are then send to fractionating column for separation
 7.Gasoline vapors are condensed in cooler and passed through stabilizer
where dissolved gases from petrol get removed.
 8.When large carbon deposited on catalyst particle it stop functioning
.Then it is reactivated in regenerator by burning off the carbon by
steam of hot air

51. ADVANTAGES OF CATALYTIC CRACKING
OVER THERMAL CRACKING
• lower temperature
• lower pressure
• more flexible
• High thermal efficiency
• Good integration of cracking and regeneration
• High yields of gasoline and other distillates
• Low gas yields
• High product selectivity
• Low n-alkane yields
• High octane number
• Chain-branching and high yield of C4 olefins
• High yields of aromatics

52. KNOCKING IN I.C. ENGINE
I.C. ENGINE
S.I. ENGINE
PETROL
C. I .ENGINE
DIESEL

53. KNOCKING
 In internal combustion engine a mixture of air
and petrol is compressed and ignited by electric
spark which causes oxidation of hydrocarbon
molecule.
 The flame should spread rapidly and smoothly
through the gases mixture and expanding gas
drives the piston down the cylinder
 But in certain cases the rate of oxidation is so
great that mixture detonates producing sound
called as engine knock
 The rate of oxidation depends upon number of
carbon atom in molecule, the structure of
molecule, and the temperature.
 The temperature depends upon compression ratio

54. KNOCKING IN I. C .ENGINE
Reasons for knocking
1.The rate of oxidation is so great that mixture
detonates producing sound called as engine
knock
2.Rate of oxidation of hydrocarbon molecules
depend upon the number of C-atoms in chain
and structure of molecule and temperature.
3.Temperature depends upon compression
ratio.
Compression ratio=v2 v1
v1 v2
Before ignition
After ignition

55. 
STROKE 1: (INTAKE)
The downward moving piston sucks a mixture of air
and petrol into the cylinder.
PETROL
ENGINE

56. STROKE 2: (COMPRESSION)
The piston moves up, compressing the gas mixture. This is
where a low octane fuel might ignite and cause knocking.
PETROL ENGINE

57. 
STROKE 3: (POWER)
Just before the piston reaches the top of the cylinder a
spark from the spark plug explodes the gas mixture.
This pushes the piston down and drives the crank shaft
round.
.
PETROL ENGINE

58. 
STROKE 4: (EXHAUST)
The piston moves up and pushes the gases out through
the exhaust valve. As the piston moves down, it pulls more
fuel/air mixture in to begin the cycle again
PETROL ENGINE

59.  The tendency of knocking depends upon the nature of fuel
and air-fuel ratio.
 Knocking tendency of different constituents of petrol are in
following order.
Straight chain alkanes > branched chain alkanes >
alkenes > naphthalenes > aromatic hydrocarbons
(Straight chain alkenes = poor antiknock property
Branched chain ,aromatic hydrocarbon = best antiknock property)
CHEMICAL STRUCTURE AND KNOCKING

60.  It is a measure of fuel tendency to knock, when burnt in spark ignition
engine.
 The straight chain hydrocarbon like n- heptane knock badly while iso-Octane
burns smoothly.Thus octane number scale is formed in which iso octane
rated as 100 (minimum knock) and heptane is 0 (bad knock).
The octane number can be increase by adding TEL,TML.The octane number
of fuel of Aroplanes 135
SCALE FOR KNOCKING IN PETROL ENGINE
(OCTANE NO.)
n – Heptane(C7H16)
OCTANE NO.= (0)
2,2,4-trimethylpentane(C8H18)
(Iso-octane)
OCTANE NO.= (100)

61. ANTIKNOCKING AGENTS
1.Tetraethyl lead(Pb(CH2CH3)4 ),TML-0.5 ml per litre
2.Methyl tertiary butyl ether(MTBE)CH3)3C-O-CH3
3.Methylcyclopentadienyl manganese tricarbonyl
C9H7MnO3
(CH3CH2)4Pb + 13 O2 → 8 CO2 + 10 H2O + Pb
Pb + CH2 Br PbBr2 + CH2
CH2 Br CH2
Ethylene bromide
Lead Bromide
Ethylene
Lead

62. WORKING OF DIESEL ENGINE
COMPRESSION IGNITION
P and T of air
P= 40 Kg/cm
2
T= 500-600 OC

70 Kg/cm
2

63. Working of diesel engine
 Diesel oil is used as fuel in diesel engine.
 In this process air is compressed to a pressure of 40-50 Kg/cm2 as
result of compression the air temperature raises to 500-600 C.
 At this stage oil is injected in the form of spray the oil droplets first get
vaporized and get heated and undergoes spontaneous ignition due to
which pressure rises to 70-100 Kg/cm2.
 If combustion of oil does not begin quickly then entire amount of oil get
injected before combustion then all of sudden entire oil burns to
produce sound called diesel knock.
 The knocking depends upon engine design and properties of diesel oil

64. SCALE FOR KNOCKING IN DIESEL ENGINE
(CETANE NO.)
Aromatic hydrocarbons> naphthalenes > alkenes
branched chain alkanes > Straight chain alkanes
CH3(CH2)14CH3
CH3
Cetane(C16H34)
CETANE NO.= (100)
-Methyl naphthalene(C11H10)
CETANE NO.= (0)

65. Cetane number test:
In this method a standard reference fuel is used
in a test cylinder. The most widely used reference
fuel is a mixture of cetane and alpha-methyl-
naphthalene. Cetane has an extremely high
ignition quality (ignites quickly) and is rated for
the test at 100. Alpha methyl-naphthalene has a
very low ignition quality (is difficult to ignite) and
is rated for the test at 0.
To increase the cetane number of diesel the
additives like acetylene ethyl nitrate acetone
diethylether are added in diesel as a preignition
fuel

66. Important hints for solving problems on combustion
 1.Always calculate weight or volume of air theoretically required
for combustion of 1 kg or 1 m3 of a fuel
 2.At S.T.P one gram mole of any gas occupies 22.4 lit.volume.
 eg. CO2=44, H2=2, CO=28, SO2=64
 3.Air contains 21%oxygen by volume and 23% by mass
 4.Air contains 79% Nitrogen by volume and 77% by mass
 5.Minimum O2 is calculated by adding O2 required for each
species.
 6.O2 present in the fuel is to be subtracted
 7.Always calculate N2 as dry product from total air supplied.
 N2 in product=N2 from fuel+N2 from air supplied
 8.Don’t consider H2O as a dry product
 9.O2 appears as a dry product only when excess air is supplied &
it is calculated from excess air only

67. Substances always combine in definite proportion. These proportions are
determined by molecular masses.
a)Weight Proportion
C(s) + O2(g) ----- CO2(g)
12 32 44
H2(g) + ½ O2(g)-----H2O(g)
02 16 18
S(s) +O2-------SO2(g)
32 32 64
b) Volume Proportion
H2(g) + ½ O2(g)-----H2O(g)
1 vol. 0.5 vol. 1 vol.
CH4 + 2O2 -----CO2+2H2O
1 vol. 2 vol. 1 vol. 2 vol.