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... high emitter profiling On-board diagnostics (OBD) ... PARAMETERS AFFECTING DIESEL PM AND HC EMISSIONS Air/Fuel ratio, generally lean overall, ... – PowerPoint PPT presentation

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Title: Bahrami_a@kaums.ac.ir


1
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2
???? ??? ???? ?????? ??? ???? ???? ???? ??????
???? ?? . ??????? ?????? ??????? ???? ?????
????? Bahrami_a_at_kaums.ac.ir
3
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5
?????? ????? ?? ????? ???? ?????? ???? ???? 1-
????? ????? ????? ??? ?? ??? ???? 2- ????? ??????
??? ?? ???? ??? 3- ????? ???? ?? ?????? ????????
?? ??? ??? 4- ????? ?????? ??? ?? ??? ????. 5-
????? ??????? ??? ????? ????? ???.
6
According to the World Health Organization
(WHO), about 2 million premature deaths are
caused each year due to air pollution in cities
across the world.
7
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8
A recent study has revealed that exposure to fine
particle matter in polluted air increases the
risk of hospitalization due to respiratory and
cardiovascular diseases
9
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10
The Atmosphere
  • 78 percent nitrogen
  • 21 percent oxygen
  • 0.09 percent Argon
  • Carbon Dioxide 0.03 percent
  • Trace elements 0.07 percent
  • Methane, ozone, hydrogen sulfide, carbon
    monoxide, etc...
  • Water vapor can range from 0 to 4

11
Air Pollution
Definition The addition of harmful substances to
the atmosphere resulting in damage to the
environment, human health, and quality of life.
Just one of many forms of pollution, air
pollution occurs inside homes, schools, and
offices in cities across continents and
globally. Ambient (outdoor) air pollution is the
focus of this presentation.
12
Stratospheric Ozone
1 atm ? 101 kPa
(From Introduction to Environmental Engineering
G. Masters, 2nd and 3rd eds.)
13
Causes of Air Pollution
Coal Plants These plants let off small,
airborne particles. These particles are known as
soot. Sulfur Dioxides are also gases given off by
these plants.
Car Exhaust The exhaust that comes out of the
tail pipe of a car contains carbon monoxide, an
odorless, colorless gas, and Nitrogen Oxide.
These gases are produced as the car burns
gasoline.
Factories Factories emit tons of harmful
chemicals into atmosphere on a daily basis.
Ammonia gases is just one emitted from these
factories.
Ozone Chemicals found in paint and hair
spray create hazardous pollutants with highly
toxic effects. These pollutants form the ground
level ozone.
Home
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  • ?? ????
  • ?? ???? ???
  • ???? ??????

17
Air Pollution I

18
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????? ?????? ???? ?? ?????? ???
2- ????? ??????? ??? ??? ?? ????? ? ????? ? ????
? ????? ?? ????? ???. 3- ????????? ?????? ??? ??
??? ???. 4- ??????? ?????? ??? ?? ??? ????.
19
An active adult inhales 10,000 to 20,000 liters
of air each day, or 7 to 14 liters every minute.
20
Types of Air Pollution
Primary air pollutants harmful chemicals that
enter directly into the atmosphere. Secondary
air pollutants harmful chemicals that form from
other substances in the atmosphere.
21
Examples of Catastrophic Air Pollution
1911 in London - 1150 died from the effects of
coal smoke. Author of the report coined the word
smog for the mix of smoke and fog that hung over
London. 1952 in London - 4000 died from smog.
1948 in Donora, Penn. Town of 14,000 people -
20 died and 6000 were ill from smog from the
community's steel mill, zinc smelter, and
sulfuric acid plant. 1963 in New York City - 300
people died from air pollution.
22
London Smog 1952
23
London Smog 1952
In 13th century London - laws against burning
outside because London was already heavily
polluted since the middle ages
24
London Smog 1952
25
A Brief History
  • 1930s-60s severe air pollution episodes Meuse
    Valley, Belgium, Donora, Pennsylvania, London,
    U.K.
  • 1960s-70s introduction of clean air legislation
  • 1970s-80s significant reduction in ambient
    concentrations of many pollutants
  • 1980s, early 1990s studies demonstrating adverse
    effects even at lower levels of exposure
  • Mid to late 1990s large number of studies
    replicated findings worldwide
  • Late 1990s-present evaluation of nuances of
    associations observed in epidemiological studies,
    effects of specific sources, biological
    mechanisms, long term effects

26
Local and Regional Pollution
  • Pollution sources tend to be concentrated in
    cities.
  • In the weather phenomenon known as thermal
    inversion, a layer of cooler air is trapped near
    the ground by a layer of warmer air above.
    Normal air mixing is greatly diminished and
    pollutants remain trapped in the lower layer.
  • Smog is intense local pollution usually trapped
    by a thermal inversion.

27
This cloud of smog was typical of the skyline
hovering over Los Angeles in the 1940s and 1950s.
28
??????? ? ????? ?????? ?????? ???
) ????? ??? ????????? ?? ??? ??? ?????? 1930 ??
??? ???? ??????? ??? ? ????? ??????????? ????? ??
?????? ???? ????????? ???? ???? ? ???? ??? 60
???????? ? ????? ????? ??? ? ?????? ??? ????.
????? ???? ??????? ???? 5 ??? ??? ????? ? ?????
??? ? ????? ?? ?????? ????? ? ???? ?????? ?????
??? ???. ???? SO2 ??? ?? ??????? ???? ?? 38
???? ?? ?????? ???? ???.
29
Severe Air Pollution Episodes
In 1948 in the steel-mill town of Donora,
Pennsylvania, intense local smog killed 19
people. In 1952 in London over 3,000 people died
in one of the notorious smog events known as
London Fogs in 1962 another 700 Londoners died
in a similar event.
Donora, PA at noon on Oct. 29, 1948 Deadly smog
envelops the town.
30
?????? ?????????? ? ?????? ?? 31 ????? 1948 ????
?????? ?????? ??? ?????? ????? ????? ??????
?????????? ?? ????? ?? ????? ????? ???? ???????
???? ?????? 6000 ??? ?? ????? 12 ???? ???? ??? ??
?? ?????? ?? ????? ????. ??? ? ?????? ?? ???
????? ???? ???? ???.
31
Denora, Pennsylvania 29 Oct 1948
32
???? ?? ? ??? (?????) 5 ?? 9 ?????? 1952 ???? ??
????????? ????? ?????? ?????? ??? ??? ?? ?? ??
?????? ???? 4000 ??? ????? ??? ? ??? ?? ???
?????? ??? ????? ??? ???. ?? ??? ????? ??? ??
????? ???? ? ??????? ??????? ?? ??? ????? ???????
??? ?????? ????? ???? ????? ??? ? ????? ??????
??? ???. ?? ???? ????? ??? ? ???? ????? ?????
????? ???????? ????? ???? ??????? ???? ? ?????
?????? ???? ???.
33
Summer 2004 ICARTT Campaign (International
Consortium for Atmospheric Research on Transport
and Transformations)
http//www.al.noaa.gov/ICARTT/
34
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35
http//www.epa.gov/airnow//health-prof/EPA_poster-
final_lo-res.pdf
36
Health Effects of Air Pollution Key Findings I
  • Know more about short term effects
  • More people die and are admitted to hospital for
    heart and lung problems on days with elevated
    levels of air pollution
  • These effects are the tip of the iceberg
    relative to other, milder effects
  • A variety of biological mechanisms have been
    identified for these effects
  • Effects found at levels previously thought to be
    safe
  • Effects observed using widely varying study
    designs large scale population studies to
    controlled laboratory studies in humans/ animals

37
Tip of the Iceberg
Adverse health effects that could be avoided
every year by meeting the US EPA's daily maximum
ozone standard (80 ppb 8-hr) in New York. Figure
sections not drawn to scale. From Thurston 1997.
38
Health Effects of Exposure to Ozone and PM2.5
Ozone PM2.5
coughing nose and throat irritation chest
pain reduced lung function increased
susceptibility to respiratory
illness aggravation of asthma children and
people with chronic lung disease are particularly
at risk
increased risk of cardiac arrest and premature
death aggravation of asthma respiratory
related hospital visits reduced lung function
and chronic bronchitis work and school
absences children and people with chronic lung
disease are particularly at risk
39
Factors which cause asthma (asthma
prevalence) Hereditary Exposure to
contaminants Cigarette smoke Obeisty Heigene A
ir Pollution? Factors which provoke asthma
(asthma attack) Cigarette Smoke Biological -
Pollen, Mold Emotional Stress Indoor Air
Quality Weather / Outdoor Air Quality
40

Effects of Air Pollution on Plants
Air pollution commonly leads to oxidation damage
of both crop plants and wild species.
41

Effects of Air Pollution on Plants
Air pollution weakens plants by damaging their
leaves, limiting the nutrients available to them,
or exposing them to toxic substances slowly
released from the soil. Quite often, injury or
death of plants is a result of these effects of
acid rain in combination with one or more
additional threats.
42
Welfare Effects of Air Pollution
43
Effects of Pollution on Buildings
For limestone, the acidic water reacts with the
calcium to form calcium sulfateCaCO3 H2SO4
CaSO4 2H CO32- The calcium
sulfate is soluble so it is easily washed away
during the next rain storm.
Statue carved in 1702 photographed in 1908 (left)
and 1969 (right).
44
Criteria Air Pollutants Ozone
  • Unpleasant appearance in urban cities
  • ? photochemical smog
  • Deterioration of synthetic rubber, textiles,
    paints

US EPA in How Stuff Works Website,
http//science.howstuffworks.com/ozone-pollution.
htm
Gates Corporation http//www.gates.com/brochure.cf
m?brochure2833location_id3369
45
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49
Major Pollutants
  • Hydrocarbons and Volatile Organic Compounds
    Gasoline, paint, solvents, cleaning solutions.
  • Carbon Monoxide Carbon Monoxide - highly
    poisonous gas attaches to hemoglobin and wont
    let go.
  • Nitrogen oxides - contribute to photochemical
    smog. Catalytic converters are designed to break
    this down.

50
Major Pollutants
  • Photochemical smog - ozone and hydrocarbons
    producing peroxyacetylnitrate.
  • Sulfur oxides - Poisonous gas to both plants and
    animals
  • Lead and other heavy metals
  • Photochemical oxidants - Toxic to plants and
    animals. Ozone is a pollutant out of place.

51
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????????? ??? ????? ??? ????? ?? ???? ??? ?? ??
????? ???? ?? ??? ????. 2- ???? ??? ?????? ????
????? ???? ?? ????? ???. 3- ???? ??? ??????
?????? ?? ??? ???. 4- ???? ??? ????? ?? ????
???. 5- ???? ??? ?????? ???? ????? ?????? ???????
?? ????? ???.
52
Why Air Pollution Control?
53
Quality of Life
  • This is what you would have lived with in Saint
    Louis in 1940.

54
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55
Quality of Life
  • This is Saint Louis today, a different kind of
    air pollution.

56
Yesterday
  • Low Pollution/High Visibility
  • High Pollution/Low Visibility

57
Two Types of Air Pollution
  • Particulate (Visible)
  • Gaseous

58
Three Types Of Control
  • Mechanical
  • Chemical
  • Biological

59
Particulates
  • Regulated Particles
  • 10 microns or less diameter
  • Human hair averages 25 microns
  • 25 microns is 1/1000 inch

60
Example Sources OfParticulate Pollution
  • Wood Processing
  • Rock Quarries
  • Coal Power Plants

61
Particulate Control(Mechanical)
  • Cyclone
  • Fabric Filter (Baghouse)
  • Scrubber
  • Electrostatic Precipitator

62
Cyclone
  • Most Common
  • Cheapest
  • Most Adaptable

63
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Cyclone Operating Principle
  • Dirty Air Enters The Side.
  • The Air Swirls Around The
  • Cylinder And Velocity Is Reduced.
  • Particulate Falls Out Of The Air To The Bottom
    Cone And Out.

65
Multiple Cyclones(Multi clone)
  • Smaller Particles Need Lower
  • Air Flow Rate To Separate.
  • Multiple Cyclones Allow
    Lower Air Flow Rate, Capture Particles to 2
    microns

66
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Fabric Filter(Baghouse)
  • Same Principle As Home Vacuum Cleaner
  • Air Can Be Blown Through Or Pulled Through
  • Bag Material Varies According To Exhaust Character

68
Baghouse
69
About Baghouses
  • Efficiency Up To 97
  • (Cyclone Efficiency 70-90)
  • Can Capture Smaller Particles Than A Cyclone
  • More Complex, Cost More To Maintain Than Cyclones

70
Electrostatic Precipitator(ESP)
  • High Efficiency
  • Able to Handle Large Air Flow Rates
  • Or Can Be Very Small (Smoke Eaters In Bars and
    Restaurants)

71
How An ESP Operates
72
Electrostatic Precipitator Drawing
73
Principle
  • High-Voltage Charges Wires
  • Gases Are Ionized
  • Particles Become Charged
  • Collection Plates (Opposite Charge) Attract
    Particles
  • Rapper Knocks Plates So That The Collected Dust
    Layer Falls Into Hoppers

74
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75
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????? ?????? ??? ?? ?? ??? ?????. 2- ?????? ?????
????? ? ?????? ?? ????? ???? ?? ????? ????. 3-
?????? ????? ????????? ?? ??? ????.
76
Scrubbers
  • Gas Contacts A Liquid Stream
  • Particles Are Entrained In The Liquid
  • May Also Be A Chemical Reaction
  • Example Limestone Slurry With Coal Power Plant
    Flue Gas

77
Tower Scrubber
78
Types Of Scrubber
  • Tray Tower Scrubbers
  • Impingement Tray
  • Sieve Tray
  • Packed Bed Scrubbers
  • Cylinder Filled with Media
  • Which Promotes Gas- Liquid Contact

79
Types Of Scrubber
  • Fiber Bed Scrubber
  • Vertical Mesh Pads Of Interlaced Fibers
    Promote Gas-Liquid Contact
  • Spray Tower Scrubber
  • Nozzles Spray Liquid Across the Inlet Gas Flow
    Path

80
Gaseous Pollutant Control
81
Pollutants Of Interest
  • Volatile Organic Compounds (VOC)
  • Nitrogen Oxides (NOx)
  • Sulfur Oxides (SOx)

82
Example Sources OfGaseous Pollutants
  • Surface Coating Processes
  • Printing
  • Combustion (Boilers)
  • Dry Cleaning
  • Bakeries

83
Mechanical Control
  • For Burners, Air/Fuel Ratio Control, Called
    Low-NOx Burners.
  • For Dry Cleaners And Similar Processes Using
    Solvent In Closed Vessels, Refrigerated
    Condensers.

84
Chemical Control
  • Flue Gas Control
  • Solvent Destruction

85
Flue Gas Control
  • To Reduce Emissions of NOx From Burners
  • Break NOx Into O2 And N2 With A Catalyst.
  • Same Process As In Autombiles.

86
Flue Gas SOx Control
  • SOx Forms Sulfuric Acid With Moisture In Air
    Producing Acid Rain.
  • Remove From Flue Gas By Chemical Reaction With
    Limestone

87
Thermal Oxidizers
  • For VOC Control
  • Also Called Afterburners

88
Two Types Of Oxidizer
  • Catalytic
  • Non-Catalytic

89
Thermal Oxidizer(Non-Catalytic)
90
Catalytic Thermal Oxidizer
91
Biological Method
  • Uses Naturally Occurring Bacteria (Bugs) To Break
    Down VOC
  • Bugs Grow On Moist Media And Dirty Gas Is
    Passed Through. Bugs Digest The VOC.
  • Result Is CO2 And H2O

92
A Bio Filter For VOC Removal
93
? Questions ?
94
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95
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????? ????. 3- ?????? ????? ???? ??? ?? ?? ?????
????? ?? ????? ????
96
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What are catalysts?
  • Simply put, catalysts are substances which, when
    added to a reaction, increase the rate of
    reaction by providing an alternate reaction
    pathway with a lower activation energy (Ea).
  • They do this by promoting proper orientation
    between reacting particles.
  • In biochemistry, catalysts are known as enzymes.

98
Catalytic Converters
  • One common application for catalysts is for
    catalytic converters.
  • Catalytic converters are found in automobiles.
  • Their role is to reduce to emissions of harmful
    gases (CO, VOCs, NOx) that are the result of the
    combustion of fuel in vehicle engines.

99
Specifics of Catalytic Converters
  • Most modern cars are equipped with three-way
    catalytic converters. "Three-way" refers to the
    three regulated emissions it helps to reduce --
    carbon monoxide, VOCs and NOx molecules.
  • The converter uses two different types of
    catalysts, a reduction catalyst and an
    oxidization catalyst. Both types consist of a
    honeycomb-shaped ceramic structure coated with a
    metal catalyst, usually platinum, rhodium and/or
    palladium.

A Reduction Catalyst B Oxidation Catalyst C
Honeycomb Ceramic Structure
100
Step 1 The Reduction Catalyst
  • The reduction catalyst is the first stage of the
    catalytic converter.
  • It uses platinum and rhodium to help reduce the
    NOx emissions. When an NO or NO2 molecule
    contacts the catalyst, the catalyst rips the
    nitrogen atom out of the molecule and holds on to
    it, freeing the oxygen in the form of O2.
  • The nitrogen atoms bond with other nitrogen atoms
    that are also stuck to the catalyst, forming N2.
  • The equation for this is as follows
  • 2 NO gt N2 O2 or 2 NO2 gt N2 2 O2

101
Step 2 The Oxidization Catalyst
  • The oxidation catalyst is the second stage of the
    catalytic converter.
  • It reduces the unburned hydrocarbons and carbon
    monoxide by burning (oxidizing) them over a
    platinum and palladium catalyst.
  • This catalyst aids the reaction of the CO and
    hydrocarbons with the remaining oxygen in the
    exhaust gas.
  • The equation for this process is as follows 2
    CO O2 gt 2 CO2
  • Once this process is complete, most of the
    harmful substances have been broken down into
    harmless ones such as N2, O2, and CO2.

102
Catalysts in Industry
  • Of course, reducing vehicle emissions is not the
    only area in which catalysts can prove useful.
    The petrochemical industry also makes great use
    of them in various processes.
  • One of these processes, called catalytic
    cracking, is detailed below. Catalytic cracking
    is the name given to the breaking up of large
    hydrocarbon molecules into smaller, more useful
    pieces.

103
Catalytic Cracking Part 1
  • Hydrocarbons are the result of the fractional
    distillation of gas oil from crude oil
    (petroleum). These fractions are obtained from
    the distillation process as liquids, but are
    re-vaporised before cracking.
  • The hydrocarbons are mixed with a very fine
    catalyst powder. These days, the catalysts are
    zeolites (complex alumniosilicates).
  • In the past, the catalyst used was aluminum oxide
    and silicon dioxide, however, these are much less
    efficient than the modern zeolite.
  • The whole mixture (hydrocarbons and zeolites) is
    blown through a reaction chamber at a temperature
    of about 500 C. The catalyst is recovered
    afterwards, and the cracked mixture is further
    separated by cooling and fractional distillation.

104
CATALYTIC CONVERTERS
  • Catalytic converters remove harmful gases from
    car exhausts.
  • It consists of a honeycomb of ceramic with metals
    such as platinum,palladium and rhodium coated on
    the honeycomb
  • It removes up to 90 of the harmful gases

Catalytic converter
CO Nox C8H18
CO2 N2 H2O
105
EQUATIONS FOR REACTIONS IN THE CATALYTIC CONVERTER
2
2
2
25
8
12 1/2
9
106
EXAMPLES OF POISONING OF CATALYSTS
Leaded petrol cannot be used in cars fitted with
a catalytic converter since lead strongly absorbs
onto the surface of the catalyst
Cannot use copper or nickel in a catalytic
converter on a car instead of the expensive
platinum or Rhodium. REASON - Any SO2 present in
the exhaust fumes (trace amounts ) would poison
the catalyst Once the catalytic converter has
become inactive it cannot be regenerated
107
  • Control of exhaust for unburned HC and CO
    involves
  • fuel modifications
  • minimizing pollutants from the combustion chamber
    - better engineering of motors
  • oxidation of pollutants outside the combustion
    chamber - either by normal combustion, or by
    catalytic oxidation. Requires pumping of air to
    the exhaust stream.

108
  • To lower NOx, two systems are used
  • exhaust gas recirculation sends part of the
    exhaust stream back into the intake manifold
    which reduces the combustion temperature and
    decreases NOx production (tolerated when
    power'' is not required)
  • a second catalytic converter can be used in
    series with the HC/CO converter to decompose NOx
    to O and N.

109
ENVE 4003
  • MOBILE SOURCES
  • Types of emissions, control technologies and
    trends, inspection and maintenance programs.

110
Motor Vehicles
  • Internal combustion (IC) engines
  • Spark ignition (SI) - gasoline, propane, natural
    gas, ethanol
  • 4-stroke vs 2-stroke
  • Compression ignition (CI) - diesel, biodiesel

111
Figure 13.1 de Nevers
  • Schematic of piston and cylinder in IC engine

112
Figure 18.2 Cooper Alley
  • Schematic of four stroke IC engine

113
Figure A3.1.5 Faiz, Weaver Walsh
  • Two stroke motorcycle engine

114
Figure A3.2.1 Faiz, Weaver Walsh
  • Diesel combustion stages

115
MOTOR VEHICLE EMISSIONS
  • Regulated (criteria pollutants)
  • CO, NOx, NMHC, PM
  • Non-regulated
  • Individual (speciated) HCs
  • carbonyl compounds (alcohols, aldehydes, ketones)
  • Air toxics, e.g. benzene, toluene, ethylbenzene,
    1,3,butadiene, formaldehyde, acetaldehyde
  • CO2 (i.e. fuel economy)

116
Table 13.1 de Nevers
  • Contribution of motor vehicles to U.S. national
    emissions

117
MOTOR VEHICLE EMISSIONS
  • Exhaust (tailpipe) (CO, NOx, VOC, PM)
  • Evaporative (VOC)
  • Resting
  • Diurnal heat build
  • Hot soak
  • Running
  • Refuelling

118
COMBUSTION IN IC ENGINES
  • Air/Fuel ratio, mass of air per mass of fuel,
    15
  • Normalized A/F ratio,
  • ? (A/F) actual / (A/F) stoichiometric
  • Equivalence ratio
  • ? (A/F)stoichiometric / (A/F) actual
  • ? ? 1 for gasoline engines most of the time,
  • ? gt 1 (fuel rich) during high power demand and
    start
  • ? lt 1 (fuel lean) for diesel most of the time,
  • ignition - combustion - extinction
  • sequence repeated 102 103 times a minute
    unsteady combustion

119
Figure (13.2) de Nevers
  • Emissions and fuel consumption vs lambda

120
Figure 10.16 (7.5) de Nevers
  • Effect of air-fuel ratio and quality of mixing on
    composition of combustion gases

121
Table 13.3 de Nevers
  • Equivalence or A/F ratios

122
POLLUTANT FORMATION MECHANISMS - SI ENGINES
  • HC
  • Rich Fuel/Air mixture, oxygen deficit
  • Flame quenching at walls, crevices, quench
    zone
  • CO
  • Rich Fuel/Air mixture, oxygen deficit
  • incomplete reaction, even with sufficient
    oxygen
  • NO, Thermal
  • ?T compression 600 F
  • ?T combustion 3600 F
  • Short times but high peak temperatures

123
DIESEL COMBUSTION CHARACTERISTICS
  • Only air is compressed during compression stroke,
    reaching 700-900 C
  • Fuel is injected into hot air just before top
    of compression stroke
  • A fuel-air mixture forms around the periphery of
    the fuel jet and ignites after an ignition delay.
    This premixed combustion phase accounts for only
    a fraction of the fuel and causes a pressure peak
  • The remainder of the fuel burns under mixing
    controlled combustion causing a more gradual
    pressure increase, and then decline with expansion

124
DIESEL NOx FORMATION CHARACTERISTICS
  • Most NOx formed during the high T and P premixed
    combustion phase
  • NOx formation can be reduced effectively by
    reducing flame temperature
  • delay combustion into the expansion phase
  • cool the air charge going into the cylinder
  • exhaust gas recirculation (EGR)

125
PARAMETERS AFFECTING DIESEL PM AND HC EMISSIONS
  • Air/Fuel ratio, generally lean overall, to allow
    for complete combustion within limited time
    available for mixing
  • Minimum ?? 1.5 for smoke point, smoke
    increases dramatically below this limit
  • Rate of air-fuel mixing, can be enhanced by
    imparting a swirl to the injected fuel
  • fuel injection timing
  • compression ratio
  • temperature and composition of charge in the
    cylinder

126
DIESEL VISIBLE SMOKE
  • Black smoke from soot
  • White, blue or gray smoke condensed hydrocarbon
    droplets in the exhaust
  • Blue or gray generally due to vaporized lubricant
  • White due to cold start
  • Sulfur in the fuel forms sulfuric acid which is
    later sampled as PM

127
Table 13.5 de Nevers
  • Comparison of gasoline and diesel engines

128
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129
VEHICLE EMISSION CONTROL
  • Control technology is aimed at reducing the
    second term fuels, engines, vehicles etc.
  • Urban and transportation planning addresses the
    first term housing density, location,
    transportation infrastructure
  • the second term is relatively insensitive to the
    number of passengers in the vehicle
  • Increasing vehicle occupancy helps reduce
    emissions mass transit, car pooling etc.

130
CONTROL TECHNOLOGY - SI
  • Air/Fuel ratio. CO and HC emissions increase as
    mixture gets richer in fuel (start and high power
    conditions), NOx emissions peak near
    stoichiometric ratio
  • Fuel metering systems carburetors and fuel
    injectors (throttle body TBI, multi-port PFI,
    simultaneous or sequential)
  • Electronic Control Systems adjust the air/fuel
    ratio based on the signal from an oxygen sensor
    in the exhaust

131
EXHAUST GAS RECIRCULATION (EGR) - SI AND CI
ENGINES
  • Dilutes Air/Fuel mixture with exhaust gases
    thereby reducing peak combustion temperatures and
    NOx formation
  • There are limits to how lean an air-fuel-exhaust
    gas mixture can be for ignition
  • Ignition systems (spark plugs etc.) and
    combustion chambers can be designed to improve
    performance with these lean mixtures

132
EXHAUST AFTERTREATMENT SI ENGINES
  • Air injection - thermal oxidation of residual CO
    and HC with excess air introduced after the
    engine into the exhaust system, very temperature
    sensitive Minumum 600 C for HC, 700 C for CO
  • Catalytic convertors can achieve conversion at
    lower temperatures 350 C
  • Oxidation (two-way) catalyst - for HC and CO
  • Oxidation-reduction (three-way) catalyst (TWC)
    for HC, CO, and NOx according to

133
CATALYTIC CONVERTORS SI ENGINES
  • Pellet and monolith types
  • Require near stoichiometric combustion for
    effective conversion of all three pollutants, CO
    and HC conversion efficieny drop for rich
    mixtures, NOx conversion efficiency drops for
    lean mixtures
  • Exhaust gas oxygen sensor (Zirconia, ZrO2 based)
    essential to keeping the Air/fuel ratio in window
    of optimum conversion efficiency for all three

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TWC picture from ICT-Umicore CD
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EVAPORATIVE EMISSION CONTROL SI ENGINES
  • Blowby and Crankcase emissions - fuel and partial
    combustion product molecules pass by the piston
    into the crankcase - recycled back to air intake
    manifold by Positive Crankcase Ventilation (PCV)
  • Charcoal canister for capturing fuel tank,
    carburetor and miscellanous evaporative
    emissions. Adsorption during hot-soak, diurnal
    heat build (breathing), refuelling periods,
    desorption into the air intake during engine
    operation (regeneration)

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CONTROL TECHNOLOGY - CI
  • PM and NOx more important in diesel exhaust than
    CO and HC, relative to gasoline exhaust
  • A general trade-off between PM and NOx exists
    although reductions in absolute levels of both
    emissions have been achieved
  • Emissions more strongly dependent on engine
    design - most emission reductions so far have
    been achieved through combustion modifications
    rather than exhaust aftertreatment in contrast
    to gasoline engine emissions

140
DIESEL PM FORMATION CHARACTERISTICS
  • Particulate Matter forms in fuel rich zones
    primarily during the mixing controlled combustion
    phase
  • mostly an aggregate chain carbon core (soot)
  • adsorbed hydrocarbons (aliphatic and
    polyaromatic) soluble organic fraction (SOF)
  • significant fraction of SOF may come from
    lubricating oil
  • Most of the PM formed during combustion is
    subsequently burned during the expansion stroke,
    the unburned part forms the emissions
  • Sulfur in the fuel forms sulfuric acid which is
    later sampled as PM

141
DIESEL EXHAUST AFTERTREATMENT
  • Flow through oxidation catalyst (two-way
    catalytic convertor) for reduction of CO and VOC
    (80), and PM SOF (20-30), does not retain PM
  • Trap oxidizer (Diesel particulate filter), reduce
    PM by 95, filter oxidation (regeneration)
    functions
  • active and passive regeneration types
  • Passive regeneration catalyst coated onto trap
    or added to fuel bring regeneration temperature
    down to 400-450 C which can be achieved in diesel
    exhaust
  • Active regeneration monitors PM build-up on the
    trap and triggers regeneration by diesel fuel
    burning, electric heating, catalyst injection

142
DPF from ICT-Umicore CD
143
DPF detail from M.Walsh
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EXHAUST EMISSION MEASUREMENT
  • Simulated driving conditions
  • Mass Emission rates in g/km for light duty
    vehicles (LDV) on a chassis dynamometer
  • Mass Emission rates in g/kWh for heavy duty (HD,
    diesel) engines on an engine dynamometer
  • Actual driving conditions
  • On-board measurement systems
  • Tunnel studies
  • Remote sensing, g/L of fuel burned

149
EVAPORATIVE EMISSION MEASUREMENT
  • SHED Test, Sealed Housing Evaporative
    Determination
  • Carbon canisters attached to various points on
    vehicle to adsorb HC vapors

150
DRIVING OR OPERATING CYCLES
  • Actual vs Synthesized
  • Transient, steady state, multi-mode
  • Modal analysis
  • Acceleration
  • Cruise
  • Deceleration
  • Idle

151
EMISSION FACTORS
  • Amount of pollutant emitted per unit activity
  • g/km, (distance travelled)
  • g/kWh, (mechanical energy delivered)
  • g/L, (quantity of fuel burned)
  • For a single vehicle with given engine and
    emission control technology, the factors that
    influence the emission factor are speed,
    acceleration/deceleration, trip length, ambient
    temperature
  • Vehicles with similar size, engine, and emission
    technology may be expected to show similar
    emission behaviour

152
EMISSION FACTORS AND EMISSION MODELLING
  • Regulated emissions from new vehicles vs
    emissions from in-use vehicles
  • Emissions surveillance program to test emissions
    from thousands of in-use vehicles at different
    ages in the U.S.
  • Emission modelling from motor vehicles involves
    the consideration of different types of vehicles
    and their driving conditions to arrive at a grand
    total

153
INSPECTION AND MAINTENANCE PROGRAMS
  • Field studies suggest that more than 50 of motor
    vehicle pollution may come from less than 10 of
    vehicles which have poorly maintained or
    malfunctioning emission control devices
  • Inspection and maintenance (I/M) programs aimed
    at identifying such gross-emitter vehicles and
    ensuring the repair of their emission control
    systems are becoming more important in the face
    of reduced emission regulations for new vehicles
  • Remote sensing of CO, HC, and NOx, along with CO2
    offers both I/M and fuel-based emission inventory
    advantages

154
I/M PROGRAMS
  • Emission control technology for LDGV very
    effective 90--95 reduction compared with no
    controls
  • Emission control system performance deteriorates
    with vehicle age but only gradually
  • Emissions from a small fraction of vehicles with
    malfunctioning control systems erode the benefits
    of emission reductions from a large number of
    vehicles
  • I/M programs aim to maintain control system
    efficiency for the entire fleet, over the useful
    life of vehicles

155
I/M PROGRAMS
  • Objectives
  • Identify and repair vehicles with maladjustments
    or control system malfunctions
  • Discourage willful tampering with control systems
  • Modes
  • Periodic checks of all vehicles
  • Identification and repair of high emitting
    vehicles,
  • Identification and exemption of low emitting
    vehicles,
  • clean screening

156
I/M PROCEDURES
  • SI Engines
  • Exhaust concentrations measurement CO, HC, NOx
  • No load, idle/2500 rpm
  • Loaded dynamometer tests
  • ASM, Acceleration simulation mode
  • (AMS2525, 25 mph, 25 maximum FTP acceleration)
  • IM240, first 240 seconds of FTP (Federal Test
    Procedure)
  • Visual inspection of control system components
  • Pressure/purge tests for evaporative emission
    control systems
  • CI Engines
  • Bosch method for smoke pull measured amount of
    exhaust through filter paper, check light
    transmission of filter
  • Opacity meter check light attenuation directly
    across exhaust path under snap acceleration
    conditions

157
I/M PROGRAMS
  • Institutional setting
  • Centralized - inspection
  • Decentralized - test and repair
  • Frequency
  • Vehicle age at first test, 1-4 years
  • Subsequent tests every 1-2 years
  • Costs
  • Program operating costs
  • Repair costs
  • Cost/benefit ratio
  • Improvement in ambient air quality vs I/M costs

158
I/M PROGRAMS - COMPLEMENTS
  • Remote sensing
  • Clean screening, high emitter profiling
  • On-board diagnostics (OBD)
  • Sensing and monitoring devices to detect
    malfunctions
  • Light indicator
  • Stored computer codes for malfunctioning
    components
  • catalyst
  • oxygen sensor
  • engine misfire
  • evaporative system integrity

159
Pb, S, and Transportation fuels
  • Pb used to be added to gasoline (tetra-ethyl lead
    TEL) as an octane enhancer.
  • Phased out in most countries and being phased out
    in others
  • permanent poisoning of TWC using leaded
    gasoline in a vehicle with TWC once is sufficient
    to make the TWC useless
  • Neuro-toxic health effects on children

160
Pb, S, and Transportation fuels
  • S is a natural component of crude oil. Can be
    removed effectively by hydrodesulfurization.
  • Adverse (though reversible) effect on efficiency
    of TWC and DPF. Low sulfur fuel increases
    efficiency of modern TWC and makes it possible to
    use advanced diesel exhaust after-treatment like
    DPF
  • contribution to PM emissions as sulfate
  • contribution to gaseous Sox emissions
  • Current trends coming down to 15 ppm (ULSD
    ultra low sulfur diesel), from 300-500 ppm.

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