1. 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

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

3. Fuels and Combustion
Fuel: Substances composed of chemical
elements which in rapid chemical union
with oxygen produced combustion.
Combustion: Is that rapid chemical union
with oxygen of an element, whose exo-
thermic heat of reaction is sufficiently
great and whose rate of reaction is suf-
ficiently fast whereby useful quantities of
heat are liberated at elevated tempera-
ture.

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

5. 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

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

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

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

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

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

11. 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)

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

13. 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)

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

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

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

17. 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.
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.

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

19. 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

20. 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.

21. 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

22. 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
+
+
=






23. 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

24. 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.00
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.

25. 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)

26. 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

27. 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
+++++
++
=






28. 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

29. 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.

30. or 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

31. 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
=






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

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

34. 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

35. 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 measuring heating
value of solid and liquid fuels.
Gas Calorimeter - instrument used for measuring heating value
of gaseous fuels.

36. 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 viscosity
to the density
d) Viscosity Index - the rate at which viscosity changes with
temperature.
e) Flash Point - the temperature at which the vapor above
a volatile liquid forms a combustible mixture with air.
f) Fire Point - The temperature at which oil gives off vapor
that burns continuously when ignited.

37. 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.

38. 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