1. FUELS
and
COMBUSTION
By. Engr. Yuri G. Melliza

2. FUELS AND COMBUSTION
 Fuels and Combustion
 Types of Fuels
 Complete/Incomplete Combustion
 Oxidation of Carbon
 Oxidation of Hydrogen
 Oxidation of Sulfur
 Air composition
 Combustion with Air
 Theoretical Air
 Hydrocarbon fuels
 Combustion of Hydrocarbon Fuel

3. Fuels and Combustion
Fuel: Substance composed of
chemical elements which in rapid
chemical union with oxygen
produced combustion.

4. Combustion:
Is that rapid chemical union with
oxygen of an element, whose
exothermic heat of reaction is
sufficiently great and whose rate
of reaction is suffi-ciently fast
whereby useful quantities of heat
are liberated at elevated
temperature.

5. TYPES OF FUELS
 Solid Fuels
ex: Wood, coal, charcoal
 Liquid Fuels
ex: gasoline, diesel, kerosene
 Gaseous Fuels
ex: LPG, Natural Gas, Methane
 Nuclear Fuels
ex: Uranium
Combustible Elements
1.Carbon (C) 3. Sulfur (S)
2.Hydrogen (H2)

6. Complete Combustion: Occurs when all
the combustible elements has been fully
oxidized.
Ex:
C + O2 → CO2
Incomplete Combustion: Occurs when
some of the combustible elements has not
been fully oxidized.
Ex:
C + O2 → CO

7. Common Combustion Gases
GAS MOLECULAR
Weight (M)
C 12
H 1
H2 2
O 16
O2 32
N 14
N2 28
S 32

8. HE COMBUSTION CHEMISTRY
Oxidation of Carbon
1183
443612
32)1(121(16)1(12)
BasisMass
111
BasisMole
COOC 2
→+
→+
+→+
→+
→+ 2

9. Oxidation of Hydrogen
981
18162
2)1(16(32)1(2)
BasisMass
11
BasisMole
OHOH
2
1
2
1
2
→+
→+
+→+
→+
→+ 22 2
1

10. Oxidation of Sulfur
211
643232
32)1(32(32)1(32)
BasisMass
111
BasisMole
OSOS
→+
→+
+→+
→+
→+
1
22

11. Composition of AIR
a. Percentages by Volume (by
mole)
O2 = 21%
N2 = 79%
b. Percentages by Mass
O2 = 23%
N2 = 77%
763
21
79
.==
2
2
OofMole
NofMoles

12. Combustion with Air
A. Combustion of Carbon with air
C + O2 + 3.76N2 → CO2 + 3.76N2
Mole Basis:
1 + 1 + 3.76 → 1+ 3.76
Mass Basis:
1(12) + 1(32) + 3.76(28) → 1(44) +
3.76(28)
12 + 32 + 3.76(28) → 44 + 3.76(28)
3 + 8 + 3.76(7) → 11+ 3.76(7)

13. kg of air per kg of Carbon:
Cofkg
airofkg
11.44=
3
3.76(7)+8
=
Cofkg
airofkg

14. B. Combustion of Hydrogen with air
H2 + ½ O2 + ½ (3.76)N2 → H2O +
½(3.76)N2
Mole Basis:
1 + ½ + ½(3.76) → 1 + ½(3.76)
Mass Basis:
1(2) + ½ (32) + ½(3.76)(28) → 1(18) +
½ (3.76)(28)
2 + 16 + 3.76(14) → 18 + 3.76(14)
1 + 8 + 3.76(7) → 9 + 3.76(7)

15. kg of air per kg of Hydrogen:
22 Hofkg
airofkg
34.32=
1
3.76(7)+8
=
Hofkg
airofkg

16. C. Combustion of Sulfur with air
S + O2 + 3.76N2 → SO2 + 3.76N2
Mole Basis:
1 + 1 + 3.76 → 1 + 3.76
Mass Basis:
1(32) + 1(32) + 3.76(28) → 1(64) +
3.76(28)
32 + 32 + 105.28 → 64 + 105.28

17. kg of air per kg of Sulfur:
Sofkg
airofkg
4.29=
32
105.2832
=
Sofkg
airofkg +

18. Theoretical Air
It is the minimum amount of air required to
oxidize the reactants or the combustible
elements found in the fuel. With theoretical
air no O2 is found in products.

19. Excess Air
It is an amount of air in excess of the
Theoretical requirements in order to
influence complete combustion. With
excess air O2 is present in the
products.

20. HYDROCARBON FUELS
Fuels containing the element s Carbon
and Hydrogen.
Chemical Formula: CnHm

21. Family Formula Structure Saturated
Paraffin CnH2n+2 Chain Yes
Olefin CnH2n Chain No
Diolefin CnH2n-2 Chain No
Naphthene CnH2n Ring Yes
Aromatic
Benzene CnH2n-6 Ring No
Naphthalene CnH2n-12 Ring No
Alcohols Note: Alcohols are not pure
hydrocarbon, because one of its
hydrogen atom is replace by an
OH radical. Sometimes it is used
as fuel in an ICE.
Methanol CH3OH
Ethanol C2H5OH

22. Saturated Hydrocarbon: All the carbon atoms are
joined by a single bond.
Unsaturated Hydrocarbon: It has two or more
adjacent Carbon atoms joined by a double or
triple bond.
Isomers: Two hydrocarbons with the same
number of carbon and hydrogen atoms but at
different structures.

23. H H H H
   
H C C C CH
   
H H H H
Chain structure Saturated
H H
| |
HC C=C C H
| | | |
H H H H
Chain Structure Unsaturated
Ring structure Saturated
H H
H C H
C C
H C H
H H

24. Theoretical Air: It is the minimum or theoretical amount
of air required to oxidized the reactants. With theoretical
air no O2 is found in the products.
Excess Air: It is an amount of air in excess of the theo-
retical air required to influence complete combustion.
With excess air O2 is found in the products.
Combustion of Hydrocarbon
Fuel(CnHm)
A. Combustion with 100% theoretical air
CnHm + aO2 + a(3.76)N2 → bCO2 + cH2O +
a(3.76)N2
fuel
air
t kg
kg
m12n
)a(3.76)(28a(32)
F
A
+
+
=






25. Combustion of Hydrocarbon Fuel
Formula: (CnHm)
A. Combustion with 100% theoretical air
CnHm + aO2 + a(3.76)N2 → bCO2 + cH2O +
a(3.76)N2
fuel
air
t kg
kg
m12n
)a(3.76)(28a(32)
F
A
+
+
=






26. fuel
air
a kg
kg
m12n
)a(3.76)(28a(32)
e)(1
F
A




+
+
+=





B. Combustion with excess air e
CnHm +(1+e) aO2 + (1+e)a(3.76)N2 → bCO2
+ cH2O + dO2 + (1+e)a(3.76)N2
Actual Air – Fuel Ratio
fuel
air
ta kg
kg
F
A
e)(1
F
A






+=





Where: e – excess air in decimal
Note: Sometimes excess air is expressible in terms of
theoretical air.
Example: 25% excess air = 125% theoretical air

27. Orsat Analysis: Orsat analysis gives the
volumetric or molal analysis of the
PRODUCTS on a DRY BASIS, (no amount of
H2O given).
Proximate Analysis: Proximate analysis
gives the amount of Fixed Carbon,
Volatiles, Ash and Moisture, in percent by
mass. Volatiles are those compounds
that evaporates at low temperature when
the solid fuel is heated.

28. ULTIMATE ANALYSIS: Ultimate analysis
gives the amount of C, H, O, N, S in
percentages by mass, and sometimes the
amount of moisture and ash are given.

29. OLID FUELS
omponents of Solid Fuels:
1. Carbon (C)
2. Hydrogen (H2)
3. Oxygen (O2)
4. Nitrogen (N2)
5. Sulfur (S)
6. Moisture (M)
7. Ash (A)

30. A.Combustion with 100% theoretical air
aC + bH2 + cO2 + dN2 + eS + fH2O + gO2 +
g(3.76)N2 → hCO2 + iH2O + jSO2 + kN2
B.Combustion with excess air x:
aC + bH2 + cO2 + dN2 + eS + fH2O +
(1+x)gO2 +(1+x)g(3.76)N2 → hCO2 +
iH2O + jSO2 + lO2 + mN2
WHERE: a, b, c, d, e, f, g, h, I, j, k, x are the
number of moles of the elements.
x – excess air in decimal

31. fuelkg
airkg
18f32e28d32c2b12a
3.76(28)g32g
F
A
t +++++
+
=





Theoretical air-fuel ratio:
Actual air-fuel ratio:
[ ]
fuelkg
airkg
18f32e28d32c2b12a
3.76(28)g32gx)(1
aF
A
+++++
++
=






32. S FLOW RATE OF FLUE GAS (Produc
Air+Fuel → Products
Without considering Ash loss






+= 1
F
A
mm Fg
Considering Ash loss






−+= lossAsh1
F
A
mm Fg

33. Heating
Value
Heating Value - is the energy released
by fuel when it is completely burned and
the products of combustion are cooled to
the original fuel temperature.
Higher Heating Value (HHV) - is the
heating value obtained when the water in
the products is liquid.
Lower Heating Value (LHV) - is the
heating value obtained when the water in
the products is vapor.

34. For Solid Fuels with the presence of
Fuel’s ULTIMATE ANALYSIS
kg
KJ
S9304
8
O
H212,144C820,33HHV 2
2 +





−+=
where: C, H2
, O2
, and S are in decimals from the
ultimate analysis

35. HHV = 31 405C + 141 647H KJ/kg
HHV = 43 385 + 93(Be - 10) KJ/kg
For Liquid Fuels
where: Be - degrees Baume
 For Coal and Oils with the absence of
Ultimate Analysis
fuelofkg
airofKg
3041
HHV
F
A
t
=






36. For Gasoline
kg
KJ)API(93639,38LHV
kg
KJ)API(93160,41HHV
°+=
°+=
kg
KJ)API(93035,39LHV
kg
KJ)API(93943,41HHV
°+=
°+=
For Kerosene

37. For Fuel Oils
InstitutePetroleumAmericanAPI
kg
KJ)API(6.139105,38LHV
kg
KJ)API(6.139130,41HHV
−
°+=
°+=

38. For Fuel Oils (From Bureau of Standard
Formula)
).t(.St@S 561500070
API131.5
141.5
S
−−=
°+
=
HHV = 51,716 – 8,793.8 (S)2
KJ/kg
LHV = HHV - QL
KJ/kg
QL
= 2442.7(9H2
) KJ/kg
H2
= 0.26 - 0.15(S) kg of H2
/ kg of fuel

39. Where
S - specific gravity of fuel oil at 15.56 °C
H2
- hydrogen content of fuel oil
QL
- heat required to evaporate and superheat the water
vapor formed bythe combustion of hydrogen in the fuel
S @ t - specific gravity of fuel oil at any temperature t
Oxygen Bomb Calorimeter - instrument used in mea-
suring heating value of solid and liquid fuels.
Gas Calorimeter - instrument used for measuring
heating value of gaseous fuels.

40. Properties of Fuels and Lubricants
a)Viscosity - a measure of the resistance to flow that a
lubricant offers when it is subjected to shear stress.
b) Absolute Viscosity - viscosity which is determined by
direct measurement of shear resistance.
c) Kinematics Viscosity - the ratio of the absolute viscos
to the density
d) Viscosity Index - the rate at which viscosity changes w
temperature.
e) Flash Point - the temperature at which the vapor above
a volatile liquid forms a combustible mixture with air.
) Fire Point - The temperature at which oil gives off vapor
that burns continuously when ignited.

41. g) Pour Point - the temperature at which oil will no
longer pour freely.
h) Dropping Point - the temperature at which grease
melts.
i) Condradson Number(carbon residue) - the
percentage amount by mass of the carbonaceous
residue remaining after destructive distillation.
j) Octane Number - a number that provides a
measure of the ability of a fuel to resist knocking
when it is burnt in a gasoline engine. It is the
percentage by volume of iso-octane in a blend with
normal heptane that matches the knocking behavior of
the fuel.

42. k) Cetane Number - a number that provides a
measure of the ignition characteristics of a diesel
fuel when it is burnt in a standard diesel engine. It is
the percentage of cetane in the standard fuel.
Prepared By: ENGR YURI G. MELLIZA, RME
XAVIER UNIVERSITY
Coralles St. Cagayan De Oro City