U5AUA10AUTOMOTIVE 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 SootLeadSulphuric OxideParticulate

Fuel

Air

Exhaust manifold

Catalytic Converter

Fuel Tank

Fuel Pump

HC

CO Solid particulate

FuelFuel

Vapors

Exhaust Gasses

14.7 – 1 AFRRicher Leaner

HC increases

NOx decreases

NOx increases

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

Light-duty Heavy-duty

Domestic Air Travel

RailwaysDomestic

MarineOther

How Global Warming Works

Fossil fuels (coal, oil, natural gas)

Carbon Dioxide (CO2)

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.

Example of the Greenhouse Effect

DifferenceGLOBAL 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

Speed limitSSS

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.

IdlingII

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 atch vehicle to needMMM

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?

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.

??

M atch vehicle to needMM

P ressurePPCheck 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% under-inflated = 12% fuel waste!

L eave your car at homeL

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.

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.

Engine tune upEE

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.

Engine tune upEE

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.

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.

ther factors OO

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.

Travel light: The heavier the vehicle, the more fuel it burns. Avoid unnecessary weight.

ther factors OO

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.

ther factors OO

Pollution from S.I. Engine

Products of Complete Products of Incomplete Combustion Combustion NOx SOx Lead CO HC Parti- Lead culates

UNIT II

I.C. Engine & Environment COx HC NOx Lead SOx Particulates CO CO2 CH4 Others N2O NO NO2 SO2 SO3 Particles Smoke Poison Aerosols Soot Poison GHG GHG Carcinogens GHG P C Smog P C Smog Visibility Acid Rain Acid Rain P C Smog OD GHG Acid Rain Visibility

Irritation

S.I. ENGINE EMISSIONS    EVAPORATIVE CRANKCASE EXHAUST FUEL CARB. CO, HC, NOX, PART. TANK FLOAT BOWL UBHC UBHC

FOR THE S.I. ENGINE WITH CARBURETOR: EVAPORATIVE EMISSIONS ACCOUNT FOR APPROXIMATELY 20% CRANKCASE EMISSIONS ACCOUNT FOR APPROXIMATELY 20% EXHAUST EMISSIONS ACCOUNT FOR THE BALANCE 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 B (for the CI Engine)Oxides of nitrogen AUnburned hydrocarbons A (for the SI Engine)Carbon monoxide A (for the SI Engine)

Global warming CFCs B (for car with A/c) (or else not involved)

Carbon dioxide B (may be even A)Methane B (may be A if CNG used)

Photochemical smog Carbon monoxide A (for the SI Engine)Unburned hydrocarbons A (for the SI Engine)Sulfur dioxide B (for the CI Engine)Oxides of nitrogen A

Ozone depletion CFCs B (for car with A/c) (or else not involved)

Unburned hydrocarbons A (for the SI Engine)Oxides of nitrogen A

A: Major contributorB: Secondary influence

EVAPORATIVE EMISSIONS

UNIT III

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

2. NO

3. 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. Equivalence Ratio2. Burned gas fraction (Residual gas plus EGR if any)3. Excess air4. Spark Timing

HC Formation:

The sequence of processes involved in the engine out HC emissions is: 1. Storage2. In-cylinder post-flame oxidation 3. Residual gas retention 4. Exhaust oxidation

HC Sources 5. 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 LP-gas.– Diesel 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

Exhaust output

HC 220 ppm

CO 1.2%

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

14.7 – 1 AFRRicher Leaner

HC increases

NOx decreases

NOx increases

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.

Fuel

Air

Exhaust manifold

Catalytic Converter

Fuel Tank

Fuel Pump

HC

CO Solid particulate

FuelFuel

Vapors

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 MechanismsThermal (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 Combustionand 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 NOxCoconut oil 7-12 -20.5Palm oil 48-55 -5Soybean oil 130 +11Sunflower oil 134 +13Rapeseed oil 101 +8Lard 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 non-

catalytic 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

Smoot, Smith, Price, Chemistry A Modern Course, 1990, page 454

N O

N O

N O

N O

N O

NO

N

O

NO

N O

N

O

N

O

O ON

NO

O

OO

N NNN

One of the reactions that takes place in the catalytic converter is the decomposition of nitrogen (II) oxide (NO) to nitrogen and oxygen gas.

N O

O

Catalytic Converter

C O

N O

CO

OCO

NN

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.

CO

N

NN

OO

OC

OCO

2 CO(g) + 2 NO(g) N2(g) + 2 CO2(g)catalyst

Enthalpy Diagram

H2O(g)

H2O(l)

H2(g) + ½ O2(g)

- 44 kJExothermic

+44 kJEndothermic

DH = +242 kJEndothermic

-242 kJExothermic

-286 kJEndothermic

DH = -286 kJExothermic

Ener

gy

H2(g) + 1/2O2(g) H2O(g) + 242 kJ DH = -242 kJKotz, Purcell, Chemistry & Chemical Reactivity 1991, page 211

Hess’s LawCalculate the enthalpy of formation of carbon dioxide from its elements.

C(g) + 2O(g) CO2(g)

Use the following data:2O(g) O2(g) DH = - 250 kJC(s) C(g) DH = +720 kJCO2(g) C(s) + O2(g) DH = +390 kJ

Smith, Smoot, Himes, pg 141

2O(g) O2(g) DH = - 250 kJ

C(g) + 2O(g) CO2(g) DH = -1360 kJ

C(g) C(s) DH = - 720 kJC(s) + O2(g) CO2(g) DH = - 390 kJ

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