The document discusses pollutant formation and control in internal combustion engines. It introduces the main pollutants from spark ignition and diesel engines as nitrogen oxides, carbon monoxide, and unburned or partially burned hydrocarbons. It then explains the formation of nitrogen oxides and emissions in diesel engines, including unburned hydrocarbons and particulate emissions. Finally, it discusses methods to control engine emissions, including engineering combustion processes, optimizing operating parameters, and using after-treatment devices like catalytic converters.

1. INTERNAL COMBUSTION ENGINES
Chapter No: 11
Pollutant formation and control
1

2. Presented by:
Ameer Hamza 2013-ME-314
Umair Ahmad 2013-ME-316
Aqib Masood 2013-ME-319
Asif Nawaz 2013-ME-331
Abdul Hannan 2013-ME-348
Presented to:
Dr. Shahid Imran
2

3. Contents
• Introduction.
• Formation of
• Emissions in diesel engine.
• Unburned hydrocarbons emissions
• Particulate emissions
• Emissions control
3

4. Introduction
• Any substance or material which causes harm to environment is
known as pollutant.
• Spark ignition and diesel engine also contribute to the air pollution.
• The amount of emissions from the engine depend on the design,
operating conditions and characteristics of the fuel.
• NOX, CO and unburned or partially burned hydrocarbons are the
main pollutants.
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5. 5

6. Formation of oxides of nitrogen
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7. Global reaction rate
The rate of change of nitric oxide concentration can be written as:
Following are the approximations to solve the above equation:
• The C-O-H system is in equilibrium and is not perturbed by N2
dissociation
• This means that the pressure, temperature, equivalence ratio and
residual fraction of fluid element only are required to calculate NO
concentration
• This means that one can solve for the N atom concentration by
setting the rate of change of atoms to zero
7

8. Emission of HC, CO and Nox in SI Engine
8

9. Emissions in diesel engine
Solids Liquids Gases
• Soot
a) Primary
particles
b)
Agglomerated
particles
c) Sulphates
• Ash
a) Oil additives
• Engine wear
particles
• Inorganic fuel
and air
contaminants
• Soluble
organic
fractions(SOF)
a) Fuel
derived
b) Oil derived
• Poly nuclear
aromatic
hydrocarbons(
PAH)
• Sulphuric acid
• Nitric oxide
(NO)
• Nitrogen
dioxide (NO2)
• Unburned
hydrocarbons
(HC)
• Carbon
monoxide(CO)
9

10. Unburned hydrocarbons emissions
• Amounts of combustion mixtures
entrapped in crevic volume
• Flame extinguishes before reaching
the cylinder wall
• Absorption of fuel hydrocarbon
before combustion and
desorption after combustion
• Bulk quenching
10

11. HC Emission mechanism in diesel engines
Fuel
AirFuel-air
mixture
Locally
overlean
mixture
Locally
overrich
mixture
Combustible
mixture
Ignition
and
flammation
Slow reaction no
ignition or flame
propagation
Bulk
quenching
Products of
incomplete
combustion
Products of
complete
combustion
For fuel injected
during delay
period
11

12. Fuel
Pyrolysis
Slow
mixing or
lack of
oxygen
Products
of
pyrolysis
Combustible
mixture
Locally
over rich
mixture
Slow
reaction, no
ignition or
flame
propagation
Flammation
Bulk
quenching
Products of
incomplete
combustion
Products of
complete
combustion
For fuel while
combustion is
occuring
12

13. Particulate emissions
• A high concentration of particulate matter (PM) is
manifested as visible smoke in the exhaust gases.
• Particulates are any substance other than water that can be
collected by filtering the exhaust, classified as:
• Solid carbon material or soot.
• Condensed hydrocarbons and their partial oxidation
products.
13

14. Continue…
• Diesel particulates consist of solid carbon (soot) at exhaust
gas temperatures below 500oC, HC compounds become
absorbed on the surface.
• In a properly adjusted SI engines soot is not usually a problem
• Particulate can arise if leaded fuel or overly rich fuel-air
mixture are used.
• Burning crankcase oil will also produce smoke especially
during engine warm up where the HC condense in the
exhaust gas.
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15. Particulate composition of diesel engine
exhaust
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16. Mechanism for the formation of particulates (soot)
• The soot formation process is very fast.
• 10 – 22 C atoms are converted into 106 C atoms in less than 1 ms.
• Based on equilibrium the composition of the fuel-oxidizer mixture soot ,
formation occurs when x ≥ 2a (or x/2a ≥ 1) in the following reaction:
• Experimentally it is found that the critica C/O ratio for onset of soot
formation is between 0.5 and 0.8.
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17. • The CO, H2, and C(s) are subsequently oxidized in the
diffusion flame to CO2 and H2O via the following
second stage.
• Any carbon not oxidized in the cylinder ends up as
soot in the exhaust
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18. Emissions control
Following are three methods to control engine emissions;
1. Engineering of combustion process -advances in fuel
injectors, oxygen sensors, and on-board computers.
2. Optimizing the choice of operating parameters -two Nox
control measures that have been used in automobile
engines are spark retard and EGR.
3. After treatment devices in the exhaust system -catalytic
converter.
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19. Catalytic Converter
• The geometry of all converters is honeycomb or pellet to
expose the exhaust gases to a large surface made of one or
more noble metals; platinum, palladium and rhodium.
• Rhodium removes NO and platinum removes HC and CO.
• Lead and sulphur in the exhaust gases inhibit the operation of
a catalytic converter(poison),
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20. Catalytic Converter
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21. Three Way Catalytic Converter
• A catalyst forces a reaction at a temperature lower than normally
occurs.
• As the exhaust gases flow through the catalyst, the NO reacts with
the CO, HC and H2 via a reduction reaction on the catalyst surface.
• NO+CO→½N2+CO2, NO+H2 → ½N2+H2O
• The remaining CO and HC are removed through an oxidation
reaction forming CO2 and H2O products (air added to exhaust after
exhaust valve).
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22. Continue…
• A three-way catalysts will function correctly only if the
exhaust gas composition corresponds to nearly (±1%)
stoichiometric combustion
• If the exhaust is too lean – NO is not destroyed
• If the exhaust is too rich – CO and HC are not destroyed
• A closed-loop control system with an oxygen sensor in the
exhaust is used to A/F ratio and used to adjust the fuel
injector so that the A/F ratio is near stoichiometric
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23. Homework Problems
Problem #01
Data :
mgasoline = 120 g /mile
mNO2 = 1.5 g
mHC = 2 g , mco = 20 g
mair = 136.23 g
To Find:
Mass concentration (NO2, HC, CO) in ppm =?
Formula:
Mass concentration =
Mass concentration in ppm = (106) ppm
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24. Calculations:
Mass of air-fuel mixture = 136.23 + 120
= 256.23 g
Mass concentration of NO2 = (106) ppm
= 5.854 × 103 ppm
Mass concentration of HC = (106) ppm
= 7.805 × 103 ppm
Mass concentration of CO = (106) ppm
= 7.805 × 104 ppm
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25. Problem#02
Data :
Ф= 1.0
rc = 8:1
L = 0.1 m
N = 1500 r.p.m
mHC = 2500 ppm
ηv = 0.8
T1 = 333K
T2 = 303K
P1 = 1 atm = 101325 Pa
P2 = 3MPa
BSFC = 300g/KW.h
To Find:
a) mf
b) Brake specific hydrocarbon emission (BSHCE)
c) BSHCE/BSFC
25

26. Formulas:
mf = BSFC × bp
bp =
BSHCE =
Calculations and Results:
a) At maximum pressure of 3MPa
bp = 58.17 KW
mf = 17451.185 g/h or 17.45 Kg /h
b) bp|p=1atm = 1.96 KW
and
BSHCE = 4.59 g/KW.h
c) BSHCE/BSFC = 0.015
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