Automative Pollution & Control

Report
U5AUA10
AUTOMOTIVE POLLUTION AND CONTROL
V SEM-AUTOMOBILE
UNIT I - Pollution
• Pollution is the introduction of contaminants
into the natural environment that cause
adverse change
• Air Pollution
• Water Pollution
• Soil pollution
• Automotive emissions have three sources:
– Evaporative
– Crankcase
– Exhaust
• Types of Emission
Exhaust Emission
Evaporative Emission
• Pollutants in Exhaust Gas
Carbon monoxide(CO)
Oxides of Nitrogen(Nox)
Hydro Carbons(HC)
Smoke and Soot
Lead
Sulphuric Oxide
Particulate
HC
Exhaust
manifold
Catalytic
Converter
CO
Solid particulate
Fuel
Tank
Air
Fuel
Vapors
Fuel
Fuel
Fuel
Pump
Exhaust Gasses
NOx increases
HC increases
Richer
NOx decreases
14.7 – 1 AFR
Leaner
Hc and Co
decreases
Adverse Health Effects of IC Engine
Generated Air Pollutants
Table 1: Sources, Health and Welfare Effects for Criteria Pollutants.
Pollutant
Description
Sources
Health Effects
Welfare Effects
Carbon
Monoxide
(CO)
Colorless, odorless
gas
Motor vehicle exhaust,
indoor sources include
kerosene or wood burning
stoves.
Headaches, reduced mental
alertness, heart attack,
cardiovascular diseases,
impaired fetal development,
death.
Contribute to the formation of
smog.
Sulfur Dioxide
(SO2)
Colorless gas that
dissolves in water
vapor to form acid,
and interact with other
gases and particles in
the air.
Coal-fired power plants,
petroleum refineries,
manufacture of sulfuric acid
and smelting of ores
containing sulfur.
Eye irritation, wheezing, chest
tightness, shortness of breath,
lung damage.
Contribute to the formation of
acid rain, visibility impairment,
plant and water damage,
aesthetic damage.
Nitrogen
Dioxide (NO2)
Reddish brown, highly
reactive gas.
Motor vehicles, electric
utilities, and other
industrial, commercial, and
residential sources that
burn fuels.
Susceptibility to respiratory
infections, irritation of the lung
and respiratory symptoms
(e.g., cough, chest pain,
difficulty breathing).
Contribute to the formation of
smog, acid rain, water quality
deterioration, global warming,
and visibility impairment.
Ozone (O3)
Gaseous pollutant
when it is formed in
the troposphere.
Vehicle exhaust and certain
other fumes. Formed from
other air pollutants in the
presence of sunlight.
Eye and throat irritation,
coughing, respiratory tract
problems, asthma, lung
damage.
Plant and ecosystem damage.
Lead (Pb)
Metallic element
Metal refineries, lead
smelters, battery
manufacturers, iron and
steel producers.
Anemia, high blood pressure,
brain and kidney damage,
neurological disorders,
cancer, lowered IQ.
Affects animals and plants,
affects aquatic ecosystems.
Particulate
Matter (PM)
Very small particles of
soot, dust, or other
matter, including tiny
droplets of liquids.
Diesel engines, power
plants, industries,
windblown dust, wood
stoves.
Eye irritation, asthma,
bronchitis, lung damage,
cancer, heavy metal
poisoning, cardiovascular
effects.
Visibility impairment,
atmospheric deposition,
aesthetic damage.
Global Climate Change
• Gas and diesel burning vehicles also contribute to global
climate change.
• The Earth’s atmosphere acts like a blanket, trapping
some of the sun’s heat near the planet’s surface.
Without this natural insulation, the average temperature
on Earth would be -18°C
• Vehicle emissions also contain CO2, an important Green
house gas (GHG).
• If the atmosphere gets too thick with GHGs, too much
heat gets trapped. That can mean problems for the
whole world.
Global Climate Change
Heavy-duty
Light-duty
Domestic
Air Travel
Railways
Domestic
Marine
Other
How Global Warming Works
Carbon Dioxide (CO2)
Fossil fuels (coal, oil, natural gas)
Example of the
Greenhouse Effect
The Sun’s energy
passes through the
car’s windshield.
This energy (heat)
is trapped inside
the car and cannot
pass back through
the windshield,
causing the inside
of the car to warm
up.
Difference
GLOBAL WARMING
is the increase of the
Earth’s average surface
temperature due to a
build-up of greenhouse
gases in the
atmosphere.
CLIMATE CHANGE
is a broader term that
refers to long-term
changes in climate,
including average
temperature and
precipitation.
Global Atmospheric Concentration of CO2
• Indian Automobile Industry
• Largest three wheeler market in the world
• 2nd largest two wheeler market in the world
• 7th largest passenger car market in Asia & 10th Largest in the
world
• 4th largest tractor market in the world
• 5th largest commercial vehicle market in the world
• 5th largest bus & truck market in the world
•
There are many actions individuals can take to
reduce their gas consumption.
• By saving gas, these actions are good for:
respiratory health, helping clean the air, fighting
climate change, and saving you money!
• Best of all, these actions are…
S.I .M. P . L. E
SS peed limit
S
S
 Reduce your driving speed: The best fuel economy for
most vehicles is 90 km/h. Reducing your speed from 100
km/h to 90 km/h improves fuel economy by 10% and from
120 km/h to 90 km/h can save 23% on fuel consumption.
Avoid aggressive driving: Aggressive driving, rapid
acceleration, or quick stops has been shown to increase
fuel use by about 39%, and saves about 4% of your time.
II dling
I
Avoid idling: Excessive idling pollutes. Turn off the engine whenever you can. If
you are stopped for more than ten seconds, turn it off. In the winter, the most
effective way to warm up a cold vehicle is to drive it. Idle for 30 seconds and then
drive away for optimum performance and fuel efficiency.
M
M atch vehicle to need
M
M
 Do you need a vehicle?: You could save yourself a lot of money and
time by evaluating if you even need a vehicle. Maybe you could take the
bus? Or walk to your destinations?
What do I need the car for?: This would help you find out what kind
of car you need. Do you need a truck for work? Do you just need
something small to get into town? Do you need a van because you have
a large family?
M
M atch vehicle to need
M
 Should I buy a used car or a new car? Older cars can be less expensive,
but can also be bad for the environment and bad on fuel. New cars produce
less emission and are more fuel efficient.
?
PP ressure
P
Check tire pressure: 5% of under-inflation = 1%
decrease in fuel efficiency. Under-inflation of 20%
will reduce the life of your tire by about 15%.
*4 tires 15%
underinflated =
12% fuel
waste!
LL eave your car at home
Reduce your number of trips: The best
way to reduce fuel use and save money is by
planning activities and combining errands to
reduce the number of trips.
EE ngine tune up
E
Regular tune-ups: A poorly tuned engine can consume an average of 10% more
fuel. One poorly tuned vehicle can emit pollutants equivalent to 20 properly tuned
vehicles.
EE ngine tune up
E
Regular tune-ups: A poorly tuned engine can consume an average of 10% more
fuel. One poorly tuned vehicle can emit pollutants equivalent to 20 properly tuned
vehicles.
Clean or replace air filters and spark plugs:
Clean filters and spark plugs help keep fuel use and
greenhouse gas emissions down.
Have your idle mixture and idle speed adjusted:
Adjusting idle speed according to vehicle
specifications on pre-1988 vehicles can decrease
greenhouse gas emissions during idling.
O ther factors
Maintain braking systems: Dragging brakes can decrease fuel efficiency by
up to 40%.
Minimize air conditioner use: Using air conditioning can increase fuel
consumption and greenhouse gas emissions by up to 21%.
Maintain wheel alignment: Make sure wheels are aligned and balanced, and
ball joints or constant velocity joints are lubricated.
O ther factors
Travel light: The heavier the vehicle, the more
fuel it burns. Avoid unnecessary weight.
 Use overdrive and high gears: While driving, strive for the lowest engine rpm at a
given road speed by selecting the highest gear in which the vehicle will operate
properly. Operate overdrive automatic transmissions in the overdrive mode.
Be aerodynamic: Reducing wind resistance on the highway by rolling up the
windows cuts fuel consumption.
O ther factors
 Have your oxygen sensor checked: Vehicles made in 1988 or after should
have the oxygen sensor checked regularly. When this sensor malfunctions, the
computer could increase the fuel ration to burn more fuel and thus increasing
greenhouse gas emissions.
 Replace or service the EGR valve: The exhaust gas recirculator (EGR) valve
reduces a variety of greenhouse gases.
Use a timed block heater: Improve fuel efficiency by 8 to 23% with a block
heater at below 0oC. Set timer for 2.5 hours before you leave.
UNIT II
Pollution from S.I. Engine
Products of Complete
Combustion
Lead
NOx
SOx
Lead
Products of Incomplete
Combustion
CO
HC
Particulates
I.C. Engine & Environment
COx
CO
Poison
HC
CO2
GHG
NOx
CH4
Others
GHG
Carcinogens
P C Smog
N2O
GHG
OD
NO
Lead
NO2
P C Smog P C Smog
GHG
Acid Rain
Poison
Visibility
SOx
SO2
Acid Rain
SO3
Particulates
Particles Smoke
Aerosols Soot
Acid Rain
Visibility
Irritation
S.I. ENGINE EMISSIONS
EVAPORATIVE
FUEL
TANK
UBHC
CARB.
FLOAT BOWL
UBHC
CRANKCASE
EXHAUST
CO, HC, NOX, PART.
FOR THE S.I. ENGINE WITH CARBURETOR:
EVAPORATIVE EMISSIONS ACCOUNT FOR APPROXIMATELY 20%
CRANKCASE EMISSIONS ACCOUNT FOR APPROXIMATELY
EXHAUST EMISSIONS ACCOUNT FOR THE BALANCE
20%
60%
Vehicular Emissions
The Internal Combustion Engine and Atmospheric Pollution
Type of Pollution
Principal Sources
Relevance of the I.C. Engine
Lead
Anti-knock compounds
A (for the SI Engine)
Carcinogens
Diesel exhaust
A
Acid Rain
Sulfur dioxide
Oxides of nitrogen
Unburned hydrocarbons
Carbon monoxide
B (for the CI Engine)
A
A (for the SI Engine)
A (for the SI Engine)
Global warming
CFCs
Carbon dioxide
Methane
B (for car with A/c)
(or else not involved)
B (may be even A)
B (may be A if CNG used)
Photochemical smog
Carbon monoxide
Unburned hydrocarbons
Sulfur dioxide
Oxides of nitrogen
A (for the SI Engine)
A (for the SI Engine)
B (for the CI Engine)
A
Ozone depletion
CFCs
B (for car with A/c)
(or else not involved)
A (for the SI Engine)
A
Unburned hydrocarbons
Oxides of nitrogen
A: Major contributor
B: Secondary influence
UNIT III
EVAPORATIVE EMISSIONS
Major Sources:
Dirunal Emissions
Take place from fuel tanks and carburetor float bowls
(in engines fitted with carburetors) of parked vehicles.
It draws in air at night as it cools down
Expels air and gasoline vapour as it heats up during the day.
These could be up to 50g per day on hot days.
Hot Soak Emissions
This occurs after an engine is shut down.
The residual thermal energy of the engine heats up
the fuel system leading to release of fuel vapours.
Running Losses
Gasoline vapours are expelled from the tank (or float bowl)
when the car is driven and the fuel tank becomes hot.
This can be high if the ambient temperature is high.
Filling Losses (Refueling Losses)
Gasoline vapours can escape
when the vehicle is being refueled in the service station.
“Evaporative emissions increase significantly
if the fuel volatility increases”
• Evaporative emissions are tested in the
“Sealed Housing Evaporative Determination – SHED” test procedure
evolved in the US.
• Vehicle is placed in the enclosure and emissions are measured as
the temperature in the fuel tank is increased.
• This gives diurnal emissions.
• Running losses are determined by running the vehicle on a chassis dynamometer
with absorbent charcoal canisters attached at various possible emission sources.
• The latest procedure involves running the vehicle through
3 standard driving cycles in the SHED.
• The hot soak test measures emissions for one hour immediately following
the hot soak test.
• Acceptable losses from the complete procedure are 2g of fuel per test
for US, Europe and India.
Evaporative Emission Control:
1.
Positive Crankcase Ventilation (PCV) System
(for crankcase emissions)
2.
Charcoal Canister System
(for Fuel tank and carburetor float bowl emissions)
Exhaust Emissions:
1.
CO
1.
NO
1.
HC
CO Formation
• Primarily dependent on the equivalence ratio.
• Levels of CO observed are lower than the maximum values
measured within the combustion chamber
• but are significantly higher than equilibrium values
for the exhaust conditions
• The processes which govern CO exhaust levels are
kinetically controlled
• The rate of re-conversion from CO to CO2 is slower than
the rate of cooling.
• This explains why CO is formed even with
stoichiometric and lean mixtures.
NO Formation:
• There is a temperature distribution across the chamber due to
passage
of flame.
• Mixture that burns early is compressed to higher temperatures after
combustion, as the cylinder pressure continues to rise.
• Mixture that burns later is compressed primarily as unburned mixture
and ends up after combustion at a lower burned gas temperature.
• Using the NO formation kinetic model based on the extended
Zeldovich mechanism:
O + N2  NO + N
N + O2  NO + O
N + OH  NO + H
• Assuming equilibrium concentrations for O, O2, N2, OH and H
corresponding to the equivalence ratio and burned gas fraction of the mixture
we obtain the rate-limited concentration profile. The NO concentration
corresponding to chemical equilibrium can also be obtained.
• The rate-controlled concentrations arise from the residual gas NO concentration,
lagging the equilibrium levels, then cross the equilibrium levels and
“freeze” well above the equilibrium values corresponding to exhaust conditions.
• Depending on details of engine operating conditions, the rate limited
concentrations may or may not come close to equilibrium levels at
peak cylinder pressure and gas temperature.
• The amount of decomposition from peak NO levels, which occurs
during expansion depends on engine conditions as well as whether
the mixture element burned early or late.
• The earlier burning fractions of the charge contribute much more to
the exhausted NO than do later burning fractions of the charge.
•
Frozen NO concentrations in these early-burning elements can be
an order of magnitude higher than concentrations in late burning elements.
•
In the absence of vigorous bulk gas motion, the highest NO
concentrations occur nearest the spark plug.
•
These descriptions of NO formation in the SI engine have been confirmed
by experimental observations.
Among the major engine variables that affect NO emissions are
1.
2.
3.
4.
Equivalence Ratio
Burned gas fraction (Residual gas plus EGR if any)
Excess air
Spark Timing
HC Formation:
The sequence of processes involved in the engine out HC emissions is:
1.
2.
3.
4.
Storage
In-cylinder post-flame oxidation
Residual gas retention
Exhaust oxidation
HC Sources
1.
Quench Layers
•
Quenching contributes to only about 5-10% of total HC. However, bulk
quenching or misfire due to operation under dilute or lean conditions
can lead to high HC.
•
Quench layer thickness has been measured and found to be in the
range of 0.05 to 0.4 mm (thinnest at high load) when using propane as
fuel.
•
Diffusion of HC from the quench layer into the burned gas and
subsequent oxidation occurs, especially with smooth clean combustion
chamber walls.
2.
Crevices
•
These are narrow volumes present around the surface of the combustion
chamber, having high surface-to-volume ratio into which flame will not
propagate.
•
They are present between the piston crown and cylinder liner, along the
gasket joints between cylinder head and block, along the seats of the intake
and exhaust valves, space around the plug center electrode and between
spark plug threads.
•
During compression and combustion, these crevice volumes are filled with
unburned charge. During expansion, a part of the UBHC-air mixture leaves
the crevices and is oxidized by the hot burned gas mixture.
•
The final contribution of each crevice to the overall HC emissions depends
on its volume and location relative to the spark plug and exhaust valve.
3.
Lubricant Oil Layer
•
The presence of lubricating oil in the fuel or on the walls of the combustion
chamber is known to result in an increase in exhaust HC levels.
•
The exhaust HC was primarily unreacted fuel and not oil or oil-derived compounds.
•
It has been proposed that fuel vapor absorption into and desorption from
oil layers on the walls of the combustion chamber could explain
the presence of HC in the exhaust.
4.
Deposits
•
Deposit buildup on the combustion chamber walls (which occurs in vehicles
over several thousand kilometers) is known to increase UBHC emissions.
•
Deposit buildup rates depend on fuel and operating conditions.
•
Olefinic and aromatic compounds tend to have faster buildup
than do paraffinic compounds.
5.
•
Liquid Fuel and Mixture Preparation – Cold Start
The largest contribution (>90%) to HC emissions from the SI engine during
a standard test occurs during the first minute of operation.
This is due to the following reasons:
•
The catalytic converter is not yet warmed up
•
A substantially larger amount of fuel is injected than the stoichiometric
proportion in order to guarantee prompt vaporization and starting
6.
Poor Combustion Quality
Flame extinction in the bulk gas before the flame front reaches the wall is a
source of HC emissions under certain engine operating conditions.
Smog
• Smog is can be a major problem in larger cities
(New York and LA)
• Smog can be harmful to
– A. Humans
– B. Plants
– C. Animals and even effect paint rubber and other
materials.
Smog
• One of largest producer of photochemical
smog is the automotive internal combustion
engine.
• The EPA (environmental protection agency)
begin putting restriction on automotive
manufactories in the mid 60.
Motor Vehicle Emissions
• Motor vehicle emission are emission produce
by motor vehicles. They include
– A. Hydrocarbons (HC)
– Carbon monoxide (CO)
– Oxides of nitrogen (NOx)
Exhaust Gasses
• Hydrocarbons (HC) are emission of unburned
petroleum products being released into the
atmosphere.
• All petroleum products and made of
hydrocarbons (hydrogen and carbon
compounds) this includes:
– Gasoline
– Diesel
LP-gas.
motor oil.
Exhaust Gasses
• Hydrocarbons are produced because of
incomplete fuel combustion or fuel
evaporation.
• Hydrocarbons emission is considered a
hazardous form of air pollution because of.
– Eye.
– Throat.
– Lung irritation.
– And possibility cancer.
Exhaust Gasses
• In north Carolina a vehicle must not exceed 220 ppm
of hydrocarbons emissions.
• High hydrocarbon emission are the results of a:
– cylinder misfire.
– Improper ignition timing
– Worn cylinder rings (pumping oil into the combustion
chamber
Exhaust Gasses
• Carbon monoxide emission are exhaust
emission that is the result of partially burned
fuel.
• A high carbon monoxide emission can be
caused by a:
– Restricted or dirty air cleaner.
– Advance ignition timing.
– Clogged fuel injectors.
Exhaust Gasses
• Oxides of nitrogen, (NOx) are emission
produced by extreme heat.
• Air consist of approximately 79% nitrogen and
21% oxygen
• When combustion chamber temperature
reaches 2500 degrees F or 1370 degrees C
nitrogen and oxygen combine to produce
oxide of nitrogen (NOx)
UNIT IV
• In North Carolina the standard for Carbon
Monoxide is 1.2 % of the total exhaust output.
Muffler
HC 220 ppm
CO 1.2%
Exhaust output
Exhaust Gasses
• Oxides of nitrogen is responsible for the dirty
brown color is SMOG.
• NOx is a eye and respiratory irritant.
• Newer high compression, learn air fuel
mixture and hotter running engine produces
more NOx than earlier engine.
Exhaust Gasses
• The same factors that increases NOx will tend to
improve fuel mileage and lower HC and CO2
production.
• This means that to increase fuel economy and lower
HC and CO2 production NOx will increase.
• For this reason emission controls have beedn added
to lower all form of emissions
Exhaust Gasses
NOx increases
HC increases
Richer
NOx decreases
14.7 – 1 AFR
Leaner
Hc and Co
decreases
Exhaust Gasses
• Before understanding emission controls we need to
first understand where they come from.
• Particulates: are solid particle of carbon soot and
fuel additives that blow out the tail pipe.
• Engine crank case blow by. Caused by heating of oil
and unburned fuel vapors that blow past the engine
rings.
Exhaust Gasses
• Fuel vapors: different chemicals that enter the
atmosphere as fuel evaporates.
• Engine exhaust gasses: are harmful chemical
that are produced inside the combustion
chamber and are blow outr the tail pipe.
HC
Exhaust
manifold
Catalytic
Converter
CO
Solid particulate
Fuel
Tank
Air
Fuel
Vapors
Fuel
Fuel
Fuel
Pump
Exhaust Gasses
• Automotive manufactures agree the best way
to lower exhaust emission is to burn all the
fuel entering the combustion chamber.
• Modern engine have introduced several
modification to ensure all fuel entering the
combustion chamber is burned.
Exhaust Gasses
• Some engine modification are:
• Lower compression ratio, by lowering compression
ratio vehicle can burn unleaded fuel. The use of
unleaded fuel allows for catalytic converters that
help reduce HC and CO emissions.
• Lower compression ratio also lower combustion
temperature reducing NOx emission.
Exhaust Gasses
• Smaller combustion chambers, allows for more heat
to remain inside the combustion chamber that can
aid in the burning of fuel.
• Reduce quench areas, the areas between the piston
and the cylinder head is the quench area. If this
areas is to close fuel will not burn completely
increasing HC and CO emissions. Modern engine are
design to reduce high quench areas.
Exhaust Gasses
Quench area
Exhaust Gasses
• Decrease valve overlap, is used to decrease
exhaust emission. A larger valve overlap
increases power but dilutes incoming fuel
mixture and requires a richer air fuel mixture
at lower engine speed therefore increasing HC
and CO emissions.
Exhaust Gasses
Overlap
Intake
Exhaust
Exhaust Gasses
• Higher combustion chamber temperature, are used
to reduce HC and CO emissions.
– Today vehicles used hot thermostats than earlier model
helping to increase combustion chamber temperature.
• Leaner air-fuel mixtures help fuel burn better lower
HC and CO emissions.
• Wider spark plug gaps, are used to burn the leaner
fuel mixture and helps prevent spark plug fouling.
Exhaust Gasses
Wider spark plug gap
Some are .080
thousands
Thermostats are
now 190 degrees
What is NOx
• NOx is actually a generic term for a group of gases called
nitrogen oxides.
• It is a mixture of gases which consists of nitric oxide (NO),
dinitrogen dioxide (N2O2), nitrous oxide (N2O), dinitrogen
trioxide (N2O3), nitrogen dioxide (NO2), dinitrogen tetroxide
(N2O4) and dinitrogen pentoxide (N2O5).
• In most high-temperature combustion processes, the
majority (95%) of NOx produced is in the form of nitric oxide
(NO)
• NOx is a major cause of ground- level ozone (smog), acid
rain, respiratory disease (emphysema and bronchitis),
water quality deterioration, and global warming.
• Worldwide biodiesel production is around 5 billion
gallons (19 billion litres) and in 2020 it will be 452.91
billion litres.
• As the use of biodiesel has increased tremendously, the
increase in NOx emissions could become a significant
barrier to market expansion.
NOx Formation Mechanisms
Thermal (Zeldovich)
prompt (Fenimore)
Fuel
N2O pathway
Thermal NOx
Thermal NO formation mechanism is the dominant source of NOx in combustion
system. It is formed by the reaction of atmospheric nitrogen with oxygen due to
combustion at elevated temperatures (above1800K).
• The three reactions producing thermal NO proposed by
Zeldovich are:
• N2 + O ↔ NO + N
(1)
• N + O2 ↔ NO + O
(2)
• N + OH ↔ NO + H
(3)
• The NO formation rate can be approximated by:
• [NO] = k e-K/T [N2] [O2]1/2 t
(4)
• Where: k and K are reaction constants, T is absolute
temperature, and t is time. The Eq. (4) indicates that thermal
NO formation is an exponential function of temperature. The
other factors that influence thermal NO formation rate are
oxygen, nitrogen concentrations and residence time of
reaction products.
Prompt NOx
• Prompt NO is generally an important mechanism in low
temperature, fuel-rich combustion processes where residence
times are short.
• The free radicals in the flame front of hydrocarbon flames
leads to rapid production of NO.
• The prompt NO contribution to total NO from combustion
process is considered less important when compared to
thermal NO. However, in biodiesel combustion, significant
quantities of NO are formed by prompt mechanism
•
•
•
•
CH + N2 ↔ HCN + N
(5)
C2 + N2 ↔ 2CN
(6)
CN+O2 ↔ NO + CO
(7)
Such reactions require relatively low activation energy and the
rate of NO formation is very rapid which is comparable to that
of the oxidation of fuel. This means that NO formation can
takes place even at much lower temperatures (below 750°C).
• The rate of HCN and NO formation increases with the
concentration of hydrocarbon radicals.
Fuel NOx
• The major source of NOx production from nitrogen-bearing
fuels such as certain coals and oil, is the conversion of fuel
bound nitrogen to NOx during combustion.
• Biodiesel molecule does not contain nitrogen in its structure
and hence formation of NOx by fuel bound oxygen is
negligible.
N2O Pathway
• In this mechanism, the atomic oxygen reacts with N2 to form
N2O by a three body reaction.
• O + N2 + M ↔ N2O + M
(8)
• where M is a molecule that is required to complete this
reaction. The N2O formed in the reaction (8) can then react to
form NO.
• N2O + O ↔ NO + NO
(9)
• This mechanism is important in combustion process under
elevated pressure and lean air fuel ratio conditions.
Reasons for Increase in NOx
• High isentropic bulk modulus of biodiesel
The high isentropic bulk modulus of biodiesel
causes an artificial advance in injection timing relative to
petrodiesel, and higher NOx emissions. However, Zhang and
Boehman found much higher NOx emissions with common rail
system, and concluded that injection timing shift alone could
not be the reason for biodiesel NOx effect.
Fuel-bound Oxygen
Biodiesel is an oxygenated fuel
containing 11% of oxygen by
weight.
High oxygen content of biodiesel promotes combustion
efficiency and reduces emissions of CO, PM, HC and other
pollutants. However, many early studies suggested that
high combustion efficiency leads to high reaction
temperature and more Thermal NOx formation.
Reduced radiative heat transfer from in-cylinder
soot
•
Biodiesel combustion generally produces lesser soot than
conventional diesel because of fuel bound oxygen, reduced
aromatic content, absence of sulphur, and unsaturated fatty
acid contents. The reduced soot formation may lessen
radiative heat transfer from soot particles which results in
elevated reaction temperature and more NOx.
• To reduce the biodiesel NOx effect, decreasing the fuel bound
oxygen content may not be the right strategy because the
presence of oxygen not only reduces particulate matter and
also mutagenicity of the soot particles.
More Stoichiometric Combustion
and High Heat Release Rate
• Mueller et al. observed increased stoichiometric burning of
biodiesel combustion which could lead to rise in temperature
and NOx.
• Higher heat release rate of biodiesel (Yu et al.)
High Adiabatic Flame Temperature
• The adiabatic flame temperature of biodiesel
is reported to have slightly higher than
petrodiesel due to complete combustion
resulting from fuel bound oxygen.
High Unsaturated Fatty Acids Content
• Iodine number (IV) is a measure of degree of unsaturation of
the fatty acid; a high iodine number indicates a high degree of
unsaturation.
• McCormick et al. investigated the relationship between NOx
emissions and Iodine value and revealed that NOx increases
with iodine value of biodiesel.
Base Oil
Iodine Value
Change in NOx
Coconut oil
7-12
-20.5
Palm oil
48-55
-5
Soybean oil
130
+11
Sunflower oil
134
+13
Rapeseed oil
101
+8
Lard Oil
62.5
+4
Higher Boiling Point of Biodiesel Fuel
• Boiling point of bio-diesel is higher than diesel fuel. Because
of higher boiling point, biodiesel retains its liquid state for an
increased duration, facilitating more droplet penetration into
the engine cylinder. This feature can lead to increased fuel
consumption, peak temperature and higher NOx.
Increased Formation of Free Radicals (Prompt
NOx)
• CH and OH radicals are continuously formed during
combustion reactions. The formation of CH-radicals is an
indicator of low temperature pre-combustion reactions, which
is the first step for the combustion process, once fuel is
evaporated. OH radicals are formed during high temperature
reactions and are located in the flame front, where
vapourized fuel reaches the highest temperatures.
• Violi et al. (Michigan University) and Brezinsky et al. (Iowa
State University) found the increased rate of CH radical
formation and lower rate of OH radical generation in biodiesel
combustion.
•
•
•
•
CH + N2 ↔ HCN + N
(5)
C2 + N2 ↔ 2CN
(6)
CN+O2 ↔ NO + CO
(7)
The increased rate of CH radical formation, lower rate of OH
radical generation and NTC (Negative temperature coefficient)
behaviour of biodiesel, indicates that biodiesel combustion is
a low temperature reaction when compared to mineral diesel
combustion. Therefore factors such as elevated adiabatic
flame temperature, higher heat release rate and
stoichiometric burning might not be the major reasons for
biodiesel NOx effect.
Biodiesel NOx Control Strategies
• Post-combustion
• Combustion control techniques
• Post Combustion Techniques
• Popular post-combustion technologies include selective noncatalytic reduction (SNCR), selective catalytic reduction (SCR)
and exhaust gas recirculation (EGR).
Selective Non-Catalytic Reduction
(SNCR)
• The process involves injecting either ammonia or urea into the flue
gas is between 1,400 and 2,000 °F (760 and 1,093 °C) to react with
the nitrogen oxides formed in the combustion process.
• NH2CONH2 + H2O -> 2NH3 + CO2
• 4 NO + 4 NH3 + O2 -> 4 N2 + 6 H2O
• At temperatures above 1093 °C ammonia decomposes:
• 4 NH3 + 5 O2 -> 4 NO + 6 H2O
• Practical constraints of temperature, time, and mixing often lead to
worse results in practice. However, selective non-catalytic reduction
has an economical advantage over selective catalytic reduction, as
the cost of the catalyst is not there.
Selective Catalytic Reduction (SCR)
• The temperature range and reaction time of Urea are reduced
with the help of catalysts.
• Oxides of base metals
(vanadium molybdenum and tungsten), zeolites, or
various precious metals.
Exhaust Gas Recirculation (EGR)
• EGR works by recirculating a portion of an engine's exhaust
gas back to the engine cylinders and hence reduces the peak
temperature and NOx.
• A drastic NOx reduction of about 41.4–65.2% at 12–20% EGR
rate was obtained with decreasing HC, smoke and CO2, but
increasing BSFC compared with neat diesel combustion
without EGR.
Combustion Control Techniques
•
•
•
•
Retardation of injection timing
Water - fuel emulsion method
Water injection method
Use of Antioxidant Additives
Retardation of Injection Timing
• Monyem et al. have shown a 35% reduction in NOx emissions
for a 6° retardation in injection and Ren and Li found a
significant reduction with preheated biodiesel.
• The ignition timing retardation also leads to an increase in
soot or PM emissions and hence would require recertification
of the engine for emissions standard compliance.
Water - fuel emulsion method
• Namasivayam et al. reported that water–
biodiesel emulsion reduces smoke and NOx
emissions significantly in CI engines. However,
the presence emulsion in fuels decreases the
volumetric energy content which causes a
reduction in fuel economy.
Water Injection Method
• Water injection into the combustion chamber is another
important method for controlling NOx emission from internal
combustion engines.
• Water injection method reduces NOx emission by up to 50%
for both diesel and biodiesel fuelled engines with a slight
increase in CO and BSFC, as well as a decrease in BTE.
Use of Antioxidant Additives
• The free radicals formation during combustion determines the
rate of reaction and prompt NOx production. Free radical is a
highly reactive molecule with one or more unpaired electrons.
• The most important reactive radicals formed during
combustion reactions are hydroperoxyl (•OOH), hydroxyl
(HO•), alkoxyl (RO•) and peroxyl (ROO•) radicals. These
radicals react with N2 and N2O forming nitrogen oxides.
Antioxidant delays or inhibits oxidative processes by donating
an electron or hydrogen atom to a radical derivative.
UNIT V
• Additions of small amounts of antioxidants
into the fuel suppress free radical formation
by reacting with peroxyl radicals to form new
inactive radicals so interrupting the
propagation step.
The hydrogen is released from the weak OH
(phenols, hydroquinones) and NH (aromatic
amines, diamines) bonds of antioxidants.
Incineration
• Incineration, also known as combustion, is most used
to control the emissions of organic compounds from
process industries.
• This control technique refers to the rapid oxidation of
a substance through the combination of oxygen with a
combustible material in the presence of heat.
• When combustion is complete, the gaseous stream is
converted to carbon dioxide and water vapor.
• Equipment used to control waste gases by
combustion can be divided in three categories:
– Direct combustion or flaring,
– Thermal incineration and
– Catalytic incineration.
Direct combustor
• Direct combustor is a device in which air and all
the combustible waste gases react at the burner.
Complete combustion must occur instantaneously
since there is no residence chamber.
• A flare can be used to control almost any emission
stream containing volatile organic compounds.
Studies conducted by EPA have shown that the
destruction efficiency of a flare is about 98 percent.
In thermal incinerators the combustible waste gases
pass over or around a burner flame into a residence
chamber where oxidation of the waste gases is
completed.
Thermal incinerators can destroy gaseous pollutants at
efficiencies of greater than 99 percent when operated
correctly.
Thermal incinerator general case
Catalytic incinerators are very similar to thermal
incinerators. The main difference is that after passing
through the flame area, the gases pass over a catalyst bed.
A catalyst promotes oxidation at lower temperatures, thereby
reducing fuel costs. Destruction efficiencies greater than 95
percent are possible using a catalytic incinerator.
Catalytic incinerator
Catalytic Converter
NO
NO
NO
N
NO
NO
O
N
N
O
N
O
N
O
O
N
O
One of the reactions that takes place in the catalytic converter
is the decomposition of nitrogen (II) oxide (NO) to nitrogen and oxygen gas.
Smoot, Smith, Price, Chemistry A Modern Course, 1990, page 454
NN
O
OO
N
O
NO
N
N
N
O
O
Catalytic Converter
2 CO(g) + 2 NO(g)
C O
C
NO
N2(g) + 2 CO2(g)
catalyst
O
N
NO
N
O C
O
O C
O
N
C
N
O
C
O
OO
One of the reactions that takes place in the catalytic converter is the decomposition of
carbon monoxide (CO) to carbon dioxide and nitrogen (II) oxide (NO) to nitrogen gas.
Enthalpy Diagram
H2(g) + ½ O2(g)
Energy
DH = +242 kJ
Endothermic
-242 kJ
Exothermic
-286 kJ
Endothermic
DH = -286 kJ
Exothermic
H2O(g)
+44 kJ
Endothermic
-44 kJ
Exothermic
H2O(l)
H2(g) + 1/2O2(g)  H2O(g) + 242 kJ
Kotz, Purcell, Chemistry & Chemical Reactivity 1991, page 211
DH = -242 kJ
Hess’s Law
Calculate the enthalpy of formation of carbon dioxide from its elements.
C(g) + 2O(g)  CO2(g)
Use the following data:
2O(g)  O22(g)
C(g) 
 C(g)
C(s)
C(s)
C(s)2(g)
+ O
 +COO2(g)
CO
2(g)
C(s)
2(g)
DH
DH
DH
C(g) + 2O(g)  CO2(g)
DH = -1360 kJ
Smith, Smoot, Himes, pg 141
=
=
=
- 250 kJ
- 720 kJ
kJ
+720
- 390 kJ
kJ
+390
CRANKCASE VENTILATION
• The problem of crankcase ventilation has existed
since the beginning of the automobile because
no piston ring, new or old, can provide a perfect
seal between the piston and the cylinder wall.
• Positive crankcase ventilation (PCV) systems
were developed to ventilate the crankcase an
recirculate the vapors to the engine’s induction
system so they can be burned in the cylinders
PCV VALVES

similar documents