Combustion is a complex series of chemical reactions, but from a physical standpoint may be described as the rapid combination of oxygen with a fuel, such as natural gas or wood, resulting in the release of heat. Most fuels contain carbon and hydrogen, and the oxygen usually comes from air.

1. FUELS AND
COMBUSTION
BY
DR. S. PUGALENDHI, EMERITUS PROFESSOR
DR. J. GITANJALI, TEACHING ASSISTANT
ER. T. AYISHA NAZIBA, I- M.TECH. (REE)

2. TYPES OF FUELS
FUELS
SOLID
AGRICULTURAL WASTE
WOOD, PEAT,
LIGNITE or BROWN COAL
BITUMINOUS COAL
ANTHRACITE, ANIMAL WASTES
LIQUID
PETROLEUM FUELS-
GASOLENE, DIESEL, FURNACE
OIL
ALCOHOL FUELS- HEAVY FUEL
OIL, METHYL ALCOHOL, ETHYL
ALCOHOL
GAS
COAL GAS, COKE OVEN GAS,
BLAST FURNACE GAS, BIOGAS,
SYN GAS, LPG, PRODUCER
GAS, NATURAL GAS

3. SOLID FUELS

4. SOLID FUELS
• Wood
• Wood charcoal
• Peat

5. WOOD
• Wood is a domestic fuel used in tropical countries
- where forests are abundant and
- other fuels are not easily and cheaply available
• Main Combustible components of wood are
Cellulose
Lignin
• Minor combustibles
Resin
Waxes
• Major inflammable component of wood
water – present up to 25-50% in freshly cut wood

7. CALORIFIC VALUE
• Ash content of wood is very low (<1%)
• Oxygen content is high (up to 45%), because of its high oxygen
content the calorific value is very low
• Calorific value of wood: 4000- 5000kcal/kg

8. CALORIFIC VALUE
• “number of heat units released when one unit of weight burnt
completely.”
• Instrument used BOMB CALORIMETER
• Formula : CV = [water equivalent × (t2-t1)] / (wt of sample)
Bomb calorimeter Weighing balance

9. COMPOSITION AND PROPERTIES OF A
TYPICAL AIR DRIED HARDWOOD
Proximate Analysis
Cellulose = 50 %
Lignin = 30 %
Resin + wax = 2%
Moisture = 15 %
Ash = 0.5 %
Water solubles = 2.5 %
Density = 650 kg/m3
Calorific value = 4,500 kcal/kg
Ultimate analysis
Carbon = 50 %
Hydrogen = 6 %
Oxygen = 44 %

10. BURNING CHARACTERISTICS OF WOOD
• Smaller pieces of wood burn more readily compared to larger
pieces
• It burns with a long non-smoky flame when burned in excess
air
• Wood fines – saw dust burns quite easily and readily
• Saw dust can be made into binderless briquettes at high
pressure
• It can be ignited easily

11. USES OF WOOD
It is used
• As domestic fuel on large scale in India and for furniture
making
• To produce wood charcoal by carbonization or destructive
distillation
• To produce producer gas by gasification

12. WOOD CHARCOAL
• Wood charcoal simply called Charcoal
• Charcoal is made by carbonization (destructive distillation) of
wood i.e. heating of wood in the absence of air at 600 oC

13. PHYSICO-CHEMICAL CHANGES DURING
WOOD CARBONIZATION
Four stages involved in the wood carbonization are
• When the temperature reaches 100-120oC, the moisture of the
wood is expelled
• At 275oC, initial decomposition of wood takes place resulting
in the formation of little distillate gas containing acetic acid and
water
• Active distillation of wood takes place up to 350oC till the
process is exothermic producing liquid products (acetic acid,
methyl alcohol, pyroligneous acid, tar etc) and gaseous
products containing carbon monoxide, carbon dioxide,
nitrogen, hydrogen, hydrocarbon etc
• From 350 to 600oC, slow evolution of residual volatile matters

14. TYPICAL PRODUCT YIELD IN WOOD
CARBONIZATION
Product Yield, % (air dried)
Charcoal 30
Pyroligneous acid
Acetic acid
Wood spirit
Water
38
8
15
15
Wood tar 10
Wood gas 22

15. USES OF CHARCOAL
• Because of its large specific surface area (150-450 m2/g) and light
and porous nature, it is used for removal of obnoxious and coloring
materials from solutions, gases, vapours, petroleum products etc by
adsorption on its surface
• It can be used as a feedstock for gasification to make producer gas
which is used for domestic and industrial heating
• It is used as a clean and smooth burning fuel in domestic heating
ovens but it is a costly fuel
• It is used very widely as a fuel for blacksmith’s and metal worker
forge furnaces /ovens
• It is a raw material for the manufacture of carbon disulphide

16. COMPOSITION OF CHARCOAL
• Carbon = 80 %
• Hydrogen = 2 %
• Oxygen and Nitrogen = 15 %
• Ash = 3 %

17. MERITS AND DEMERITS OF CHARCOAL AS
FUEL
MERITS DEMERITS
It has a very high specific surface area
compared to coal (20 – 200 m2/gm)
Its ash content is very low (<3 %)
Its calorific value is high (7500 – 8000
kcal/kg)
Its mechanical strength is poor, hence it
gets crushed to powder in operation which
is easily swept away in a current of gases
and also it may prevent the proper flow of
gases in the furnace

18. PEAT
• Peat is the first stage in the formation of coal from wood
(cellulose)
• It can be termed as the most immature coal
• It has been formed by gradual decaying of vegetable matter in
moist places
• It appears light brown and fibrous at the surface but with
increase in depth of color becomes darker and the vegetable
structure disappears

19. COMPOSITION OF PEAT
• It varies from place to place depending upon the nature of
original vegetable matter, depth of deposit and age
• Peat contains
Moisture = 90 %
Solids = 10 %
• It can be used as fuel after reducing the moisture content to 30
%

20. TYPICAL COMPOSITION OF FRESHLY MINED
PEAT
• Moisture = 85 %
• Volatile matter = 8 %
• Fixed carbon = 4 %
• Ash = 3 %
• Calorific value = 650 kcal/kg

21. TYPICAL COMPOSITION OF SUN DRIED PEAT
(ON AIR DRIED BASIS)
Proximate analysis
• Moisture = 20 %
• Volatile matter = 50 %
• Fixed carbon = 25 %
• Ash = 5 %
• Calorific value = 5000 kcal/kg
Ultimate analysis
• Carbon = 55 %
• Hydrogen = 6 %
• Oxygen = 35 %
• Nitrogen = 3 %
• Sulphur = 1 %

22. OCCURRENCE OF PEAT
• Russia has the largest deposit of peat (60 % of the world
reserve) in the world
• Other countries – Germany, Finland, Poland, America, Sweden,
Norway, Ireland, etc
• India has a very small deposit of peat in Nilgiri hills and two
sides of Hooghly river in and around Calcutta

23. BURNING CHARACTERISTICS OF PEAT
• Its bulk density is very low (ie. 300 kg/m3). Hence its
transportation cost is high
• Its friable nature causes appreciable losses on handling prior to
its burning
• It offers low furnace temperature and efficiency due to its low
calorific value

24. COMPARATIVE ANALYSIS OF PEAT
CHARCOAL AND WOOD CHARCOAL
Wood charcoal Peat charcoal
Carbon, % 85 84
Hydrogen, % 3 2
Oxygen and
Nitrogen, %
3.5 8
Ash , % 2.5 3
Moisture, % 6 3
Heating value,
kcal/kg
7500 7000

25. PULVERIZED COAL
• Pulverizing means powdering
• The rate of combustion of solid fuels is slow because of the
difficulty of contact between the fuel and the oxygen
• The combustion rate can be increased by Pulverizing the fuel so
that air and fuel come in close contact easily

26. ADVANTAGES OF PULVERIZED COAL
• It can be intimately and uniformly mixed with air necessary for
combustion and hence it can be burnt completely
• It can be handled with ease like liquid fuel and transported
through pipes
• Furnace temperature can be easily controlled by increasing or
decreasing the rate of burning through a valve just like
liquid/gaseous fuel
• The atmosphere inside the furnace can be easily maintained as
oxidizing or reducing which is of great advantage in
metallurgical furnaces
• Wide varieties of coals can be used

27. • Low grade coals can be used with precaution because high ash
content carrying dust and grit into atmosphere
• Combustion is completed with low percentage of excess air,
hence high flame temperature and high efficiency can be
achieved
• Maximum efficiency is possible because of close regulation of
rate of fuel and supply of air by automatic control
• Labour charges are low and maintenance is largely exterior to
the furnace
• It imparts greater flexibility of control. Besides banking and
stand-by losses are minimum

28. DISADVANTAGES OF PULVERIZED COAL
• Cost of drying and grinding to fine size is relatively higher
• Fine dust is discharged into atmosphere along with the chimney gas
• There is a tendency for slagging on refractory walls and furnace
linings
• It requires larger combustion space to complete the combustion
• Furnace stock/work can be contaminated by ash from coal
• Its use results in erosion of pressure in boiler parts by fly ash
entrained in flue gases resulting in reduced availability and high
maintenance cost of boiler
• Heavy erosion damage of induced draft fan blades by entrained ash
in the flue gas occurs
• Operation and maintenance cost of pulveriser is high

29. PULVERIZED COAL COMBUSTION
MECHANISM
Pulverized coal undergoes complete combustion in three stages
• As the volatile matter is evolved some change in shape and size
of particles occurs in the pre-ignition stage
• Thereafter the ignition and combustion of volatile matter
occurs
• Finally the combustion of carbonaceous residue occurs

30. ULTIMATE ANALYSIS AND CV OF SOLID
FUELS
FUEL ULTIMATE ANALYSIS, % by mass GROSS
CV
(kcal/kg
)
C H2 O2 N2 S Ash/inc
ombusti
bles
Wood
(dry)
48.5 6.0 43.5 0.5 -- 1.5 2500
Lignite 66.0 5.0 20.0 1.0 1.0 3.5 5000
Bitumin
ous coal
81.0 5.0 8.0 1.5 1.5 3.5 7500

31. LIQUID FUELS

32. KEROSENE
• Heavier than gasoline
• Used in lamps, heaters and stoves
• Fuel for CI engine and for aircraft gas turbines
• Same as to Jet fuels- used in aircraft turbines and jet engines
• Specific gravity : 0.78 – 0.85
• Distillation range : 300-500°F

33. DISTILLATE
• Slightly heavier than kerosene
• Found in some western US
• Obtained from distillation at atmospheric pressure
• Used in lamps, heaters and stoves

34. DIESEL OIL
• Petroleum fractions lie between kerosene and the lubricating oil
• Wide range of specific gravity and distillation range
• Composition can controlled to make them suitable for use in
various types of CI engines

35. FUEL OIL
• Wide range of specific gravity and distillation range
• Composition does not require accurate control because they
are used in continuous burners
•

36. LUBRICATING OILS
• Partly obtained from heavy distillates of petroleum
• Partly from residual oil
• Residual oil-oils remaining after distillation
• Tars, asphalt-solid or semisolid which remain un-distilled

37. PETROLEUM
• Petroleum is a naturally occurring brown to black oil
comprising mainly of hydrocarbons found under the crust of
the earth on-shore or off-shore
• It obtained from the ground either by natural seepage or by
drilling wells to various depths
• Liquid petroleum fuels use in SI Engine
• Specific gravity range between 0.7 –0.78
• Chemical composition varies widely based on the crude
methods used in refining

38. COMPOSITION OF PETROLEUM
• Carbon = 84 – 87%
• Hydrogen = 11 – 15 %
• Sulphur = 0.1 – 3%
• Nitrogen = 0.1 -1.5%
• Oxygen = 0.3 – 1.8 %

39. PRINCIPAL COMPONENTS OF PETROLEUM
• Hydrocarbons (paraffins, napthenes, aromatics, olefins, etc)
• Small amounts of sulphur, nitrogen and oxygen compounds as
impurities
• Some inorganic compounds and metals (vanadium and
platinum in traces)

40. DETECTION OF PETROLEUM DEPOSITS
Petroleum deposits are detected by following methods
• Visual
• Geophysical
• Geological
• Drilling

41. CONTAMINANTS OF CRUDE OIL
• Crude oil as it comes out of well may contain up to
• 25 % water
• Salts (Mg Cl2, CaCl2, NaCl etc) up to 2000-5000 mg/l
• Sediments up to 1-1.5 %

42. CRUDE OIL REFINING
• For refining crude oil
• The salt content should be < 50mg/l and
• Water < 0.3 %
• Extra water in crude requires extra heat for its distillation,
increase its cost of transportation, forms emulsion which
absorb materials like resin
• Salt in crude oil causes scaling, corrosion and reduces heat
transfer coefficient during its processing
• Sediments present in crude causes erosion and scaling

43. METHODS OF SEPARATION OF IMPURITIES
FROM CRUDE OIL
• Three methods
• Mechanical method
In Mechanical method of separation of impurities from crude oil, it is
subjected to centrifuging, filtration and settling after heating it to 120 -
160oC at 6-8 atmospheric pressure
• Physico-chemical method
In Physico-chemical method, emulsion breakers are added. They are costly and
cause corrosion and sludge formation
• Electrical dehydration method
In electrical dehydration method of crude oil, 10 % water is added to
crude and it is heated before passing it through an electrical dehydrator which
has two concentric metal plates as electrodes in which 30000 volts is supplied
thereby separating water from crude
First dehydrator →T= 90-95oC, P= 6.8 atm

44. STABILIZATION OF CRUDE OIL
• It is the process of removal of dissolved gases from crude oil by
heating
• The purpose of the process is to avoid breathing loss
• Breathing loss- loss of gasoline
• Breathing loss is about 0.4 – 0.75 kg/m3 of tank per month

45. TRANSPORTATION OF CRUDE OIL
• Pipe lines
• Rail road (tank cars)
• Tankers
• Tank truck
• Barges (small tankers)
• Underwater super tankers (in marine ships-used for inter-
continental transport)

46. PETROLEUM AND ITS PRODUCTS
TRANSPORTATION PIPELINES EXISTINGIN
INDIA
Crude oil pipelines Petroleum Product Pipelines
(a)Bombay high to Bombay
(b)Salaya (Gujarat) to Mathura
(U.P.)
(c)Guwahati to Baruni (Bihar)
(a)Haldia to Baruni to Kanpur
(b)Haldia to Rajbandh near
Durgapur)
(c)Mathura to Jalandhar
(d)Viramgam to Ahmedabad
(e)Bombay to Pune
(f)Guwahati to Silliguri (W.B)

47. CLASSIFICATION OF PETROLEUM
Depending on the nature of hydrocarbons present, petroleum is
classified as
• Paraffinic crude petroleum oil
• Naphthenic crude petroleum oil
• Asphaltic (aromatic) crude oil
• Mixed crude oil containing all paraffinic, napthenic and
aromatic constituents.

48. REFINING OF PETROLEUM
• Pre-treated crude oil is heated in pipes in a furnace and its vapours
are passed through a tall cylindrical fractioning column which has a
number of plates inside it
• As the petroleum vapor moves upward , the higher boiling point
fractions condense and fall back and only lower boiling point vapors
move to higher plates where further condensation takes place and
some more liquid falls back
• As the freshly condensed liquid comes to the lower plates it gets
heated and vaporized and again condenses on higher plates
• This process of condensation and vaporization takes place many
times causing separation of the constituents of petroleum according
to their boiling points

49. DISTILLATION
• → Refinery gas (LPG) mainly propane and butane (-160 to -40 oC)
• → Gasoline or petrol (30 -200 oC)
• → Naptha (120-200 oC)
• → Solvent Spirit (125-250 oC ) or, Jet fuel (130-260 oC)
• → Kerosene (140-300 oC)
• → Gas oil (180-350 oC)
• → Lubricating oil (200-350 oC)
• → Petrolatum (220-350 oC)
• → Light fuel oil (> 200 oC)
• → Heavy fuel oil (> 250 oC)
• → Road making bitumen or tar
• → Wax
• → Residue pitch/coke

50. ULTIMATE ANALYSIS AND CV OF LIQUID
FUELS
FUEL ULTIMATE ANALYSIS, % by mass Specific
gravity
at 15.6
0C
Stoichio
metric
Fuel-air
ratio
GROSS
CV,
kJ/kg
C H2 O2 N2 S Ash
Gasolene
C8 H18
84.7 15.3 -- -- -- -- 0.707 0.0665 44241
Diesel 86.1 12.0 -- -- 0.9 -- 0.876 0.0666 42450
Ethyl
alcoh ol
C2 H5OH
52.1 13.1 34.8 -- -- -- 0794 0.111 26865
Methyl
alcohol
CH3 OH
37.5 12.5 50.0 -- -- -- 0.796 0.155 19957
Heavy
fuel oil
86.1 11.8 -- -- 2.1 -- 0.95 -- 43953

51. VOLUMETRIC COMPOSITION AND CV OF
GASEOUS FUELS
FUEL PERCENT COMPOSITION BY VOLUME Stoichi
ometri
c
Fuel-
air
ratio
GROSS
CV,
kJ/kg
H2 CO CH4 C2 H4 C2 H6 C6H6 O2 N2 CO2
Blast
furnac
e gas
1.0 27.5 -- -- -- -- -- 60.0 11.5 2698
Blue
Water
gas
47.3 37.0 1.3 -- -- -- 0.7 8.3 5.4 13909
Coal
gas
54.5 10.9 24.2 1.5 -- 1.3 0.2 4.4 3.0 34425
Coke
oven
gas
46.5 6.3 32.1 3.5 -- 0.5 0.8 8.1 2.2 35355
Natura
l gas
-- -- 83.4 -- 15.8 -- -- 0.8 -- 50707

52. PROPERTIES OF SOME COMMONLY USED
HYDRO-CARBON FUELS
NAME CHEMICAL FORMULA SPECIFIC GRAVITY
at 15.6 0C
LOWER HEAT VALUE,
kJ/kg
STOICHIOMETRIC
FUEL-AIR RATIO
Hydrogen H2 0.069 120040 0.418
Methane CH4 0.552 49963 0.105
Ethane C2H6 1.03 47450 0.058
Propane C3H8 1.52 46325 0.0419
Butane C4H10 2.00 45690 0.0323
Acetylene C2H2 0.897 48311 0.0837
Carbon
monoxiide
CO 0.966 10106 0.0418
Air -- 1.00 -- --

53. ESTIMATION OF CV OF FUELS
Sl. No. FUEL HIGHER CALORIFIC
VALUE, kcal/kg
LOWER CALORIFIC
VALUE, kcal/kg
1 C 8100 --
2 CO 2430 --
3 S 2220 --
4 H2 34400 29900
Standard Formula
If the composition of the fuel is : carbon - C%, carbon monoxide- CO%,
sulphur – S%, and oxygen – O%, then calorific value per kg of fuel is given by
8100 C + 34400 {H – (O/8) } + 2220 S
= --------------------------------------------------
---------
100

54. DULONG AND BOIE FORMULA
Dulong has suggested the following empirical formula for
calculating the higher calorific value of fossil fuels( coal, petrol,
diesel etc.).
1
HCV = ----- [8080 C + 34500 {H – (O/8) } + 2220 S ],
100
where HCV is in kcal/kg
Boie has suggested the following formula for Agricultural
Residues
1
HCV = ----- [35160 C + 116225 H – 11090 O + 6280 N + 10465 S ]

55. CALORIFIC VALUE OF FUELS
• CV – heat liberated while burning 1 kg of a liquid or solid fuel. The
unit in SI system – kJ/kg
• For gaseous fuels, it is expressed in kJ/m3
• HHV- Higher Heating Value or Higher Calorific value
• The heat transferred when H2O in the products is in the liquid state.
• LHV- Lower Heating Value or Lower Calorific value
• The heat transferred in the reaction when H2O in the products is in
the vapour state
• LHV = HHV – mH2O . hfg
• Where mH2O is the mass of water formed in the reaction.

56. CV AT CONSTANT VOLUME AND CV AT
CONSTANT PRESSURE
• When a fuel is burnt in a heat-insulated vessel, it burns at
constant volume. Heat liberated is stored as internal energy in
the products of combustion
• When a fuel is burnt at constant pressure, the external work is
said to be done
• By first law of thermodynamics, Q=dU+pdV
• i.e.heat liberated = change in internal energy + external work
done
• Let the change in volume produced by combustion be ‘n’ mols
per mol of fuel supplied. For a molar gas, pV = MRT = 8.3143
T

57. CV AT CONSTANT VOLUME AND CV AT
CONSTANT PRESSURE
When ‘n’ is equal to zero, the heat liberated by the fuel is equal
to the calorific value per mol which is also the heat liberated at
constant volume. When ‘n’ is not equal to zero, the change in
internal energy is recorded as the calorific value per mole and is
different from the heat liberated by the fuel.
i.e. CV at constant volume = 1.986 nT + CV at constant
pressure

58. PROPERTIES OF FUELS (SPECIFIC HEAT AT
CONSTANT
VOLUME AND CONSTANT PRESSURE)
• Specific heat at
constant volume
(kJ/kg K) : Heat reqd
to raise the temp of a
unit mass of gas thru
one degree when it is
heated at constant
volume
• Qv = mcv (T2-T1). All
the heat added is
converted into internal

59. PROPERETIES OF FUEL
• Specific heat at constant pressure (kJ/kg K) : Heat required to raise the
temperature of a unit mass of gas through one degree when it is heated at
constant pressure
Qp = mcp (T2-T1)
• A part of the heat added is used to do some external work (pV/J) and the rest is
used to raise the temp of the gas i.e to increase the internal energy of the gas
ENTAHLPY : h = U + pV
• Molar Specific heat of a Gas : Amount of heat needed to raise the temperature of
unit mole of a gas through one degree
• Molar Specific heat at constant volume = Mcv
• Molar Specific heat at constant pressure = Mcp
• Where M is the molecular mass (kg mol)
• Thermal Capacity or Heat Capacity (kJ) : The heat needed to raise the
temperature of the whole mass of a substance through one degree; HC= m c ; m

60. Water equivalent of a substance : The amount of water , which requires the same heat as
the substance to raise its temperature through one degree
W.E. = moisture content; m = mass of the substance, kg; c = specific heat , kJ/kgK
Regnault’s law states that the two specific heats of a gas does not vary with the change in
pressure and temperature of the gas
Joule’ law states that the change in the internal energy of a perfect gas is directly
proportional to the change of temperature dE = mc(T2-T1)
Gas and Vapour
A gas may be defined as the state of a substance whose evaporation from liquid
state is complete
A vapour may be defined the state of a substance whose evaporation from liquid state is
partial. Eg steam, CO2, SO2 &NH3
Universal Gas Constant, RM (RM = M R)
The product of the relative molecular mass and the characteristic gas constant of all
gases is always a constant

61. VALUES OF CP AND CV FOR COMMON
GASES
Name of gas cp cv  = cp / cv
Air 1.000 0.720 1.40
CO2 0.846 0.657 1.29
O2 0.913 0.653 1.39
N2 1.043 0.745 1.40
NH3 2.177 1.692 1.29
CO 1.047 0.749 1.40
H2 14.257 10.133 1.40
Ar 0.523 0.314 1.67
He 5.234 3.153 1.66
CH4 2.169 1.650 1.31

62. JUNKERS GAS CALORIMETER

63. FUELS USED IN BOILERS
• Solid fuels : wood, coal, briquettes, agricultural Wastes, etc.
• Liquid fuels : Furnace oil, diesel, kerosene, etc
• Gaseous fuels: Producer gas, Biogas, Natural Gas, etc.